Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports.
Currently information about the reporting task's held locks and IRQ
trace events are shown, if they are enabled.
Signed-off-by: Marco Elver <[email protected]>
Suggested-by: Qian Cai <[email protected]>
---
v3:
* Typos
v2:
* Rework obtaining 'current' for the "other thread" -- it now passes
'current' and ensures that we stall until the report was printed, so
that the lockdep information contained in 'current' is accurate. This
was non-trivial but testing so far leads me to conclude this now
reliably prints the held locks for the "other thread" (please test
more!).
---
kernel/kcsan/core.c | 4 +-
kernel/kcsan/kcsan.h | 3 ++
kernel/kcsan/report.c | 103 +++++++++++++++++++++++++++++++++++++++++-
lib/Kconfig.kcsan | 13 ++++++
4 files changed, 120 insertions(+), 3 deletions(-)
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index e7387fec66795..065615df88eaa 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -18,8 +18,8 @@
#include "kcsan.h"
static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
-static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
-static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
+unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
+unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
index 892de5120c1b6..e282f8b5749e9 100644
--- a/kernel/kcsan/kcsan.h
+++ b/kernel/kcsan/kcsan.h
@@ -13,6 +13,9 @@
/* The number of adjacent watchpoints to check. */
#define KCSAN_CHECK_ADJACENT 1
+extern unsigned int kcsan_udelay_task;
+extern unsigned int kcsan_udelay_interrupt;
+
/*
* Globally enable and disable KCSAN.
*/
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index 11c791b886f3c..7bdb515e3662f 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -1,5 +1,7 @@
// SPDX-License-Identifier: GPL-2.0
+#include <linux/debug_locks.h>
+#include <linux/delay.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/lockdep.h>
@@ -31,7 +33,26 @@ static struct {
int cpu_id;
unsigned long stack_entries[NUM_STACK_ENTRIES];
int num_stack_entries;
-} other_info = { .ptr = NULL };
+
+ /*
+ * Optionally pass @current. Typically we do not need to pass @current
+ * via @other_info since just @task_pid is sufficient. Passing @current
+ * has additional overhead.
+ *
+ * To safely pass @current, we must either use get_task_struct/
+ * put_task_struct, or stall the thread that populated @other_info.
+ *
+ * We cannot rely on get_task_struct/put_task_struct in case
+ * release_report() races with a task being released, and would have to
+ * free it in release_report(). This may result in deadlock if we want
+ * to use KCSAN on the allocators.
+ *
+ * Since we also want to reliably print held locks for
+ * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
+ * that populated @other_info until it has been consumed.
+ */
+ struct task_struct *task;
+} other_info;
/*
* Information about reported races; used to rate limit reporting.
@@ -245,6 +266,16 @@ static int sym_strcmp(void *addr1, void *addr2)
return strncmp(buf1, buf2, sizeof(buf1));
}
+static void print_verbose_info(struct task_struct *task)
+{
+ if (!task)
+ return;
+
+ pr_err("\n");
+ debug_show_held_locks(task);
+ print_irqtrace_events(task);
+}
+
/*
* Returns true if a report was generated, false otherwise.
*/
@@ -319,6 +350,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
other_info.num_stack_entries - other_skipnr,
0);
+ if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
+ print_verbose_info(other_info.task);
+
pr_err("\n");
pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
get_access_type(access_type), ptr, size,
@@ -340,6 +374,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
0);
+ if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
+ print_verbose_info(current);
+
/* Print report footer. */
pr_err("\n");
pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
@@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
spin_unlock_irqrestore(&report_lock, *flags);
}
+/*
+ * Sets @other_info.task and awaits consumption of @other_info.
+ *
+ * Precondition: report_lock is held.
+ * Postcondition: report_lock is held.
+ */
+static void
+set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)
+{
+ /*
+ * We may be instrumenting a code-path where current->state is already
+ * something other than TASK_RUNNING.
+ */
+ const bool is_running = current->state == TASK_RUNNING;
+ /*
+ * To avoid deadlock in case we are in an interrupt here and this is a
+ * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
+ * timeout to ensure this works in all contexts.
+ *
+ * Await approximately the worst case delay of the reporting thread (if
+ * we are not interrupted).
+ */
+ int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
+
+ other_info.task = current;
+ do {
+ if (is_running) {
+ /*
+ * Let lockdep know the real task is sleeping, to print
+ * the held locks (recall we turned lockdep off, so
+ * locking/unlocking @report_lock won't be recorded).
+ */
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ }
+ spin_unlock_irqrestore(&report_lock, *flags);
+ /*
+ * We cannot call schedule() since we also cannot reliably
+ * determine if sleeping here is permitted -- see in_atomic().
+ */
+
+ udelay(1);
+ spin_lock_irqsave(&report_lock, *flags);
+ if (timeout-- < 0) {
+ /*
+ * Abort. Reset other_info.task to NULL, since it
+ * appears the other thread is still going to consume
+ * it. It will result in no verbose info printed for
+ * this task.
+ */
+ other_info.task = NULL;
+ break;
+ }
+ /*
+ * If @ptr nor @current matches, then our information has been
+ * consumed and we may continue. If not, retry.
+ */
+ } while (other_info.ptr == ptr && other_info.task == current);
+ if (is_running)
+ set_current_state(TASK_RUNNING);
+}
+
/*
* Depending on the report type either sets other_info and returns false, or
* acquires the matching other_info and returns true. If other_info is not
@@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
other_info.cpu_id = cpu_id;
other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
+ if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
+ set_other_info_task_blocking(flags, ptr);
+
spin_unlock_irqrestore(&report_lock, *flags);
/*
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
index 081ed2e1bf7b1..0f1447ff8f558 100644
--- a/lib/Kconfig.kcsan
+++ b/lib/Kconfig.kcsan
@@ -20,6 +20,19 @@ menuconfig KCSAN
if KCSAN
+config KCSAN_VERBOSE
+ bool "Show verbose reports with more information about system state"
+ depends on PROVE_LOCKING
+ help
+ If enabled, reports show more information about the system state that
+ may help better analyze and debug races. This includes held locks and
+ IRQ trace events.
+
+ While this option should generally be benign, we call into more
+ external functions on report generation; if a race report is
+ generated from any one of them, system stability may suffer due to
+ deadlocks or recursion. If in doubt, say N.
+
config KCSAN_DEBUG
bool "Debugging of KCSAN internals"
--
2.25.0.265.gbab2e86ba0-goog
On Sat, Feb 22, 2020 at 12:10:27AM +0100, Marco Elver wrote:
> Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports.
> Currently information about the reporting task's held locks and IRQ
> trace events are shown, if they are enabled.
>
> Signed-off-by: Marco Elver <[email protected]>
> Suggested-by: Qian Cai <[email protected]>
Applied in place of v1, thank you! Please check -rcu's "dev" branch
to make sure that I have correct ordering and versions.
Thanx, Paul
> ---
> v3:
> * Typos
> v2:
> * Rework obtaining 'current' for the "other thread" -- it now passes
> 'current' and ensures that we stall until the report was printed, so
> that the lockdep information contained in 'current' is accurate. This
> was non-trivial but testing so far leads me to conclude this now
> reliably prints the held locks for the "other thread" (please test
> more!).
> ---
> kernel/kcsan/core.c | 4 +-
> kernel/kcsan/kcsan.h | 3 ++
> kernel/kcsan/report.c | 103 +++++++++++++++++++++++++++++++++++++++++-
> lib/Kconfig.kcsan | 13 ++++++
> 4 files changed, 120 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> index e7387fec66795..065615df88eaa 100644
> --- a/kernel/kcsan/core.c
> +++ b/kernel/kcsan/core.c
> @@ -18,8 +18,8 @@
> #include "kcsan.h"
>
> static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
> -static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> -static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> +unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> +unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
> static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
>
> diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
> index 892de5120c1b6..e282f8b5749e9 100644
> --- a/kernel/kcsan/kcsan.h
> +++ b/kernel/kcsan/kcsan.h
> @@ -13,6 +13,9 @@
> /* The number of adjacent watchpoints to check. */
> #define KCSAN_CHECK_ADJACENT 1
>
> +extern unsigned int kcsan_udelay_task;
> +extern unsigned int kcsan_udelay_interrupt;
> +
> /*
> * Globally enable and disable KCSAN.
> */
> diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
> index 11c791b886f3c..7bdb515e3662f 100644
> --- a/kernel/kcsan/report.c
> +++ b/kernel/kcsan/report.c
> @@ -1,5 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0
>
> +#include <linux/debug_locks.h>
> +#include <linux/delay.h>
> #include <linux/jiffies.h>
> #include <linux/kernel.h>
> #include <linux/lockdep.h>
> @@ -31,7 +33,26 @@ static struct {
> int cpu_id;
> unsigned long stack_entries[NUM_STACK_ENTRIES];
> int num_stack_entries;
> -} other_info = { .ptr = NULL };
> +
> + /*
> + * Optionally pass @current. Typically we do not need to pass @current
> + * via @other_info since just @task_pid is sufficient. Passing @current
> + * has additional overhead.
> + *
> + * To safely pass @current, we must either use get_task_struct/
> + * put_task_struct, or stall the thread that populated @other_info.
> + *
> + * We cannot rely on get_task_struct/put_task_struct in case
> + * release_report() races with a task being released, and would have to
> + * free it in release_report(). This may result in deadlock if we want
> + * to use KCSAN on the allocators.
> + *
> + * Since we also want to reliably print held locks for
> + * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
> + * that populated @other_info until it has been consumed.
> + */
> + struct task_struct *task;
> +} other_info;
>
> /*
> * Information about reported races; used to rate limit reporting.
> @@ -245,6 +266,16 @@ static int sym_strcmp(void *addr1, void *addr2)
> return strncmp(buf1, buf2, sizeof(buf1));
> }
>
> +static void print_verbose_info(struct task_struct *task)
> +{
> + if (!task)
> + return;
> +
> + pr_err("\n");
> + debug_show_held_locks(task);
> + print_irqtrace_events(task);
> +}
> +
> /*
> * Returns true if a report was generated, false otherwise.
> */
> @@ -319,6 +350,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> other_info.num_stack_entries - other_skipnr,
> 0);
>
> + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> + print_verbose_info(other_info.task);
> +
> pr_err("\n");
> pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
> get_access_type(access_type), ptr, size,
> @@ -340,6 +374,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> 0);
>
> + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> + print_verbose_info(current);
> +
> /* Print report footer. */
> pr_err("\n");
> pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
> @@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
> spin_unlock_irqrestore(&report_lock, *flags);
> }
>
> +/*
> + * Sets @other_info.task and awaits consumption of @other_info.
> + *
> + * Precondition: report_lock is held.
> + * Postcondition: report_lock is held.
> + */
> +static void
> +set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)
> +{
> + /*
> + * We may be instrumenting a code-path where current->state is already
> + * something other than TASK_RUNNING.
> + */
> + const bool is_running = current->state == TASK_RUNNING;
> + /*
> + * To avoid deadlock in case we are in an interrupt here and this is a
> + * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
> + * timeout to ensure this works in all contexts.
> + *
> + * Await approximately the worst case delay of the reporting thread (if
> + * we are not interrupted).
> + */
> + int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
> +
> + other_info.task = current;
> + do {
> + if (is_running) {
> + /*
> + * Let lockdep know the real task is sleeping, to print
> + * the held locks (recall we turned lockdep off, so
> + * locking/unlocking @report_lock won't be recorded).
> + */
> + set_current_state(TASK_UNINTERRUPTIBLE);
> + }
> + spin_unlock_irqrestore(&report_lock, *flags);
> + /*
> + * We cannot call schedule() since we also cannot reliably
> + * determine if sleeping here is permitted -- see in_atomic().
> + */
> +
> + udelay(1);
> + spin_lock_irqsave(&report_lock, *flags);
> + if (timeout-- < 0) {
> + /*
> + * Abort. Reset other_info.task to NULL, since it
> + * appears the other thread is still going to consume
> + * it. It will result in no verbose info printed for
> + * this task.
> + */
> + other_info.task = NULL;
> + break;
> + }
> + /*
> + * If @ptr nor @current matches, then our information has been
> + * consumed and we may continue. If not, retry.
> + */
> + } while (other_info.ptr == ptr && other_info.task == current);
> + if (is_running)
> + set_current_state(TASK_RUNNING);
> +}
> +
> /*
> * Depending on the report type either sets other_info and returns false, or
> * acquires the matching other_info and returns true. If other_info is not
> @@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
> other_info.cpu_id = cpu_id;
> other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
>
> + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> + set_other_info_task_blocking(flags, ptr);
> +
> spin_unlock_irqrestore(&report_lock, *flags);
>
> /*
> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> index 081ed2e1bf7b1..0f1447ff8f558 100644
> --- a/lib/Kconfig.kcsan
> +++ b/lib/Kconfig.kcsan
> @@ -20,6 +20,19 @@ menuconfig KCSAN
>
> if KCSAN
>
> +config KCSAN_VERBOSE
> + bool "Show verbose reports with more information about system state"
> + depends on PROVE_LOCKING
> + help
> + If enabled, reports show more information about the system state that
> + may help better analyze and debug races. This includes held locks and
> + IRQ trace events.
> +
> + While this option should generally be benign, we call into more
> + external functions on report generation; if a race report is
> + generated from any one of them, system stability may suffer due to
> + deadlocks or recursion. If in doubt, say N.
> +
> config KCSAN_DEBUG
> bool "Debugging of KCSAN internals"
>
> --
> 2.25.0.265.gbab2e86ba0-goog
>
On Sat, 22 Feb 2020 at 02:36, Paul E. McKenney <[email protected]> wrote:
>
> On Sat, Feb 22, 2020 at 12:10:27AM +0100, Marco Elver wrote:
> > Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports.
> > Currently information about the reporting task's held locks and IRQ
> > trace events are shown, if they are enabled.
> >
> > Signed-off-by: Marco Elver <[email protected]>
> > Suggested-by: Qian Cai <[email protected]>
>
> Applied in place of v1, thank you! Please check -rcu's "dev" branch
> to make sure that I have correct ordering and versions.
(Missed this.) Checked, and all looks good. Thank you!
I hope the new version of this patch now does what you'd expect.
Thanks,
-- Marco
>
> > ---
> > v3:
> > * Typos
> > v2:
> > * Rework obtaining 'current' for the "other thread" -- it now passes
> > 'current' and ensures that we stall until the report was printed, so
> > that the lockdep information contained in 'current' is accurate. This
> > was non-trivial but testing so far leads me to conclude this now
> > reliably prints the held locks for the "other thread" (please test
> > more!).
> > ---
> > kernel/kcsan/core.c | 4 +-
> > kernel/kcsan/kcsan.h | 3 ++
> > kernel/kcsan/report.c | 103 +++++++++++++++++++++++++++++++++++++++++-
> > lib/Kconfig.kcsan | 13 ++++++
> > 4 files changed, 120 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> > index e7387fec66795..065615df88eaa 100644
> > --- a/kernel/kcsan/core.c
> > +++ b/kernel/kcsan/core.c
> > @@ -18,8 +18,8 @@
> > #include "kcsan.h"
> >
> > static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
> > -static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> > -static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> > +unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> > +unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> > static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
> > static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
> >
> > diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
> > index 892de5120c1b6..e282f8b5749e9 100644
> > --- a/kernel/kcsan/kcsan.h
> > +++ b/kernel/kcsan/kcsan.h
> > @@ -13,6 +13,9 @@
> > /* The number of adjacent watchpoints to check. */
> > #define KCSAN_CHECK_ADJACENT 1
> >
> > +extern unsigned int kcsan_udelay_task;
> > +extern unsigned int kcsan_udelay_interrupt;
> > +
> > /*
> > * Globally enable and disable KCSAN.
> > */
> > diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
> > index 11c791b886f3c..7bdb515e3662f 100644
> > --- a/kernel/kcsan/report.c
> > +++ b/kernel/kcsan/report.c
> > @@ -1,5 +1,7 @@
> > // SPDX-License-Identifier: GPL-2.0
> >
> > +#include <linux/debug_locks.h>
> > +#include <linux/delay.h>
> > #include <linux/jiffies.h>
> > #include <linux/kernel.h>
> > #include <linux/lockdep.h>
> > @@ -31,7 +33,26 @@ static struct {
> > int cpu_id;
> > unsigned long stack_entries[NUM_STACK_ENTRIES];
> > int num_stack_entries;
> > -} other_info = { .ptr = NULL };
> > +
> > + /*
> > + * Optionally pass @current. Typically we do not need to pass @current
> > + * via @other_info since just @task_pid is sufficient. Passing @current
> > + * has additional overhead.
> > + *
> > + * To safely pass @current, we must either use get_task_struct/
> > + * put_task_struct, or stall the thread that populated @other_info.
> > + *
> > + * We cannot rely on get_task_struct/put_task_struct in case
> > + * release_report() races with a task being released, and would have to
> > + * free it in release_report(). This may result in deadlock if we want
> > + * to use KCSAN on the allocators.
> > + *
> > + * Since we also want to reliably print held locks for
> > + * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
> > + * that populated @other_info until it has been consumed.
> > + */
> > + struct task_struct *task;
> > +} other_info;
> >
> > /*
> > * Information about reported races; used to rate limit reporting.
> > @@ -245,6 +266,16 @@ static int sym_strcmp(void *addr1, void *addr2)
> > return strncmp(buf1, buf2, sizeof(buf1));
> > }
> >
> > +static void print_verbose_info(struct task_struct *task)
> > +{
> > + if (!task)
> > + return;
> > +
> > + pr_err("\n");
> > + debug_show_held_locks(task);
> > + print_irqtrace_events(task);
> > +}
> > +
> > /*
> > * Returns true if a report was generated, false otherwise.
> > */
> > @@ -319,6 +350,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> > other_info.num_stack_entries - other_skipnr,
> > 0);
> >
> > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > + print_verbose_info(other_info.task);
> > +
> > pr_err("\n");
> > pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
> > get_access_type(access_type), ptr, size,
> > @@ -340,6 +374,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> > stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> > 0);
> >
> > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > + print_verbose_info(current);
> > +
> > /* Print report footer. */
> > pr_err("\n");
> > pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
> > @@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
> > spin_unlock_irqrestore(&report_lock, *flags);
> > }
> >
> > +/*
> > + * Sets @other_info.task and awaits consumption of @other_info.
> > + *
> > + * Precondition: report_lock is held.
> > + * Postcondition: report_lock is held.
> > + */
> > +static void
> > +set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)
> > +{
> > + /*
> > + * We may be instrumenting a code-path where current->state is already
> > + * something other than TASK_RUNNING.
> > + */
> > + const bool is_running = current->state == TASK_RUNNING;
> > + /*
> > + * To avoid deadlock in case we are in an interrupt here and this is a
> > + * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
> > + * timeout to ensure this works in all contexts.
> > + *
> > + * Await approximately the worst case delay of the reporting thread (if
> > + * we are not interrupted).
> > + */
> > + int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
> > +
> > + other_info.task = current;
> > + do {
> > + if (is_running) {
> > + /*
> > + * Let lockdep know the real task is sleeping, to print
> > + * the held locks (recall we turned lockdep off, so
> > + * locking/unlocking @report_lock won't be recorded).
> > + */
> > + set_current_state(TASK_UNINTERRUPTIBLE);
> > + }
> > + spin_unlock_irqrestore(&report_lock, *flags);
> > + /*
> > + * We cannot call schedule() since we also cannot reliably
> > + * determine if sleeping here is permitted -- see in_atomic().
> > + */
> > +
> > + udelay(1);
> > + spin_lock_irqsave(&report_lock, *flags);
> > + if (timeout-- < 0) {
> > + /*
> > + * Abort. Reset other_info.task to NULL, since it
> > + * appears the other thread is still going to consume
> > + * it. It will result in no verbose info printed for
> > + * this task.
> > + */
> > + other_info.task = NULL;
> > + break;
> > + }
> > + /*
> > + * If @ptr nor @current matches, then our information has been
> > + * consumed and we may continue. If not, retry.
> > + */
> > + } while (other_info.ptr == ptr && other_info.task == current);
> > + if (is_running)
> > + set_current_state(TASK_RUNNING);
> > +}
> > +
> > /*
> > * Depending on the report type either sets other_info and returns false, or
> > * acquires the matching other_info and returns true. If other_info is not
> > @@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
> > other_info.cpu_id = cpu_id;
> > other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
> >
> > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > + set_other_info_task_blocking(flags, ptr);
> > +
> > spin_unlock_irqrestore(&report_lock, *flags);
> >
> > /*
> > diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> > index 081ed2e1bf7b1..0f1447ff8f558 100644
> > --- a/lib/Kconfig.kcsan
> > +++ b/lib/Kconfig.kcsan
> > @@ -20,6 +20,19 @@ menuconfig KCSAN
> >
> > if KCSAN
> >
> > +config KCSAN_VERBOSE
> > + bool "Show verbose reports with more information about system state"
> > + depends on PROVE_LOCKING
> > + help
> > + If enabled, reports show more information about the system state that
> > + may help better analyze and debug races. This includes held locks and
> > + IRQ trace events.
> > +
> > + While this option should generally be benign, we call into more
> > + external functions on report generation; if a race report is
> > + generated from any one of them, system stability may suffer due to
> > + deadlocks or recursion. If in doubt, say N.
> > +
> > config KCSAN_DEBUG
> > bool "Debugging of KCSAN internals"
> >
> > --
> > 2.25.0.265.gbab2e86ba0-goog
> >
On Mon, Feb 24, 2020 at 08:16:47PM +0100, Marco Elver wrote:
> On Sat, 22 Feb 2020 at 02:36, Paul E. McKenney <[email protected]> wrote:
> >
> > On Sat, Feb 22, 2020 at 12:10:27AM +0100, Marco Elver wrote:
> > > Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports.
> > > Currently information about the reporting task's held locks and IRQ
> > > trace events are shown, if they are enabled.
> > >
> > > Signed-off-by: Marco Elver <[email protected]>
> > > Suggested-by: Qian Cai <[email protected]>
> >
> > Applied in place of v1, thank you! Please check -rcu's "dev" branch
> > to make sure that I have correct ordering and versions.
>
> (Missed this.) Checked, and all looks good. Thank you!
>
> I hope the new version of this patch now does what you'd expect.
Indeed it does! Please see below for one example from an rcutorture
run.
Thanx, Paul
------------------------------------------------------------------------
[ 3.162466] ==================================================================
[ 3.162989] BUG: KCSAN: data-race in mutex_spin_on_owner+0xc6/0x2b0
[ 3.162989]
[ 3.162989] race at unknown origin, with read to 0xffff8e91dde0d838 of 4 bytes by task 156 on cpu 3:
[ 3.162989] mutex_spin_on_owner+0xc6/0x2b0
[ 3.162989] __mutex_lock+0x252/0xc70
[ 3.162989] mutex_lock_nested+0x27/0x30
[ 3.162989] ata_eh_acquire+0x32/0x80
[ 3.162989] ata_msleep+0x72/0xa0
[ 3.162989] sata_link_debounce+0xed/0x1e0
[ 3.162989] sata_link_resume+0x146/0x1b0
[ 3.162989] sata_link_hardreset+0x16c/0x290
[ 3.162989] ahci_do_hardreset+0x19b/0x220
[ 3.162989] ahci_hardreset+0x3e/0x70
[ 3.168849] ata5: SATA link down (SStatus 0 SControl 300)
[ 3.162989] ata_do_reset+0x35/0xa0
[ 3.162989] ata_eh_reset+0x77b/0x1300
[ 3.162989] ata_eh_recover+0x433/0x2090
[ 3.162989] sata_pmp_error_handler+0x86a/0xef0
[ 3.162989] ahci_error_handler+0x7c/0xd0
[ 3.162989] ata_scsi_port_error_handler+0x3ef/0xb90
[ 3.162989] ata_scsi_error+0x185/0x1d0
[ 3.162989] scsi_error_handler+0x13f/0x710
[ 3.172310] ata3.00: ATAPI: QEMU DVD-ROM, 2.5+, max UDMA/100
[ 3.162989] kthread+0x1c3/0x1e0
[ 3.162989] ret_from_fork+0x3a/0x50
[ 3.162989]
[ 3.162989] 2 locks held by scsi_eh_3/156:
[ 3.162989] #0: ffff8e91ddef90d0 (&host->eh_mutex){+.+.}, at: ata_eh_acquire+0x32/0x80
[ 3.162989] #1: ffffffff86067ba0 (rcu_read_lock){....}, at: mutex_spin_on_owner+0x0/0x2b0
> Thanks,
> -- Marco
>
> >
> > > ---
> > > v3:
> > > * Typos
> > > v2:
> > > * Rework obtaining 'current' for the "other thread" -- it now passes
> > > 'current' and ensures that we stall until the report was printed, so
> > > that the lockdep information contained in 'current' is accurate. This
> > > was non-trivial but testing so far leads me to conclude this now
> > > reliably prints the held locks for the "other thread" (please test
> > > more!).
> > > ---
> > > kernel/kcsan/core.c | 4 +-
> > > kernel/kcsan/kcsan.h | 3 ++
> > > kernel/kcsan/report.c | 103 +++++++++++++++++++++++++++++++++++++++++-
> > > lib/Kconfig.kcsan | 13 ++++++
> > > 4 files changed, 120 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> > > index e7387fec66795..065615df88eaa 100644
> > > --- a/kernel/kcsan/core.c
> > > +++ b/kernel/kcsan/core.c
> > > @@ -18,8 +18,8 @@
> > > #include "kcsan.h"
> > >
> > > static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
> > > -static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> > > -static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> > > +unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> > > +unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> > > static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
> > > static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
> > >
> > > diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
> > > index 892de5120c1b6..e282f8b5749e9 100644
> > > --- a/kernel/kcsan/kcsan.h
> > > +++ b/kernel/kcsan/kcsan.h
> > > @@ -13,6 +13,9 @@
> > > /* The number of adjacent watchpoints to check. */
> > > #define KCSAN_CHECK_ADJACENT 1
> > >
> > > +extern unsigned int kcsan_udelay_task;
> > > +extern unsigned int kcsan_udelay_interrupt;
> > > +
> > > /*
> > > * Globally enable and disable KCSAN.
> > > */
> > > diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
> > > index 11c791b886f3c..7bdb515e3662f 100644
> > > --- a/kernel/kcsan/report.c
> > > +++ b/kernel/kcsan/report.c
> > > @@ -1,5 +1,7 @@
> > > // SPDX-License-Identifier: GPL-2.0
> > >
> > > +#include <linux/debug_locks.h>
> > > +#include <linux/delay.h>
> > > #include <linux/jiffies.h>
> > > #include <linux/kernel.h>
> > > #include <linux/lockdep.h>
> > > @@ -31,7 +33,26 @@ static struct {
> > > int cpu_id;
> > > unsigned long stack_entries[NUM_STACK_ENTRIES];
> > > int num_stack_entries;
> > > -} other_info = { .ptr = NULL };
> > > +
> > > + /*
> > > + * Optionally pass @current. Typically we do not need to pass @current
> > > + * via @other_info since just @task_pid is sufficient. Passing @current
> > > + * has additional overhead.
> > > + *
> > > + * To safely pass @current, we must either use get_task_struct/
> > > + * put_task_struct, or stall the thread that populated @other_info.
> > > + *
> > > + * We cannot rely on get_task_struct/put_task_struct in case
> > > + * release_report() races with a task being released, and would have to
> > > + * free it in release_report(). This may result in deadlock if we want
> > > + * to use KCSAN on the allocators.
> > > + *
> > > + * Since we also want to reliably print held locks for
> > > + * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
> > > + * that populated @other_info until it has been consumed.
> > > + */
> > > + struct task_struct *task;
> > > +} other_info;
> > >
> > > /*
> > > * Information about reported races; used to rate limit reporting.
> > > @@ -245,6 +266,16 @@ static int sym_strcmp(void *addr1, void *addr2)
> > > return strncmp(buf1, buf2, sizeof(buf1));
> > > }
> > >
> > > +static void print_verbose_info(struct task_struct *task)
> > > +{
> > > + if (!task)
> > > + return;
> > > +
> > > + pr_err("\n");
> > > + debug_show_held_locks(task);
> > > + print_irqtrace_events(task);
> > > +}
> > > +
> > > /*
> > > * Returns true if a report was generated, false otherwise.
> > > */
> > > @@ -319,6 +350,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> > > other_info.num_stack_entries - other_skipnr,
> > > 0);
> > >
> > > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > > + print_verbose_info(other_info.task);
> > > +
> > > pr_err("\n");
> > > pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
> > > get_access_type(access_type), ptr, size,
> > > @@ -340,6 +374,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> > > stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> > > 0);
> > >
> > > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > > + print_verbose_info(current);
> > > +
> > > /* Print report footer. */
> > > pr_err("\n");
> > > pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
> > > @@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
> > > spin_unlock_irqrestore(&report_lock, *flags);
> > > }
> > >
> > > +/*
> > > + * Sets @other_info.task and awaits consumption of @other_info.
> > > + *
> > > + * Precondition: report_lock is held.
> > > + * Postcondition: report_lock is held.
> > > + */
> > > +static void
> > > +set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)
> > > +{
> > > + /*
> > > + * We may be instrumenting a code-path where current->state is already
> > > + * something other than TASK_RUNNING.
> > > + */
> > > + const bool is_running = current->state == TASK_RUNNING;
> > > + /*
> > > + * To avoid deadlock in case we are in an interrupt here and this is a
> > > + * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
> > > + * timeout to ensure this works in all contexts.
> > > + *
> > > + * Await approximately the worst case delay of the reporting thread (if
> > > + * we are not interrupted).
> > > + */
> > > + int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
> > > +
> > > + other_info.task = current;
> > > + do {
> > > + if (is_running) {
> > > + /*
> > > + * Let lockdep know the real task is sleeping, to print
> > > + * the held locks (recall we turned lockdep off, so
> > > + * locking/unlocking @report_lock won't be recorded).
> > > + */
> > > + set_current_state(TASK_UNINTERRUPTIBLE);
> > > + }
> > > + spin_unlock_irqrestore(&report_lock, *flags);
> > > + /*
> > > + * We cannot call schedule() since we also cannot reliably
> > > + * determine if sleeping here is permitted -- see in_atomic().
> > > + */
> > > +
> > > + udelay(1);
> > > + spin_lock_irqsave(&report_lock, *flags);
> > > + if (timeout-- < 0) {
> > > + /*
> > > + * Abort. Reset other_info.task to NULL, since it
> > > + * appears the other thread is still going to consume
> > > + * it. It will result in no verbose info printed for
> > > + * this task.
> > > + */
> > > + other_info.task = NULL;
> > > + break;
> > > + }
> > > + /*
> > > + * If @ptr nor @current matches, then our information has been
> > > + * consumed and we may continue. If not, retry.
> > > + */
> > > + } while (other_info.ptr == ptr && other_info.task == current);
> > > + if (is_running)
> > > + set_current_state(TASK_RUNNING);
> > > +}
> > > +
> > > /*
> > > * Depending on the report type either sets other_info and returns false, or
> > > * acquires the matching other_info and returns true. If other_info is not
> > > @@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
> > > other_info.cpu_id = cpu_id;
> > > other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
> > >
> > > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > > + set_other_info_task_blocking(flags, ptr);
> > > +
> > > spin_unlock_irqrestore(&report_lock, *flags);
> > >
> > > /*
> > > diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> > > index 081ed2e1bf7b1..0f1447ff8f558 100644
> > > --- a/lib/Kconfig.kcsan
> > > +++ b/lib/Kconfig.kcsan
> > > @@ -20,6 +20,19 @@ menuconfig KCSAN
> > >
> > > if KCSAN
> > >
> > > +config KCSAN_VERBOSE
> > > + bool "Show verbose reports with more information about system state"
> > > + depends on PROVE_LOCKING
> > > + help
> > > + If enabled, reports show more information about the system state that
> > > + may help better analyze and debug races. This includes held locks and
> > > + IRQ trace events.
> > > +
> > > + While this option should generally be benign, we call into more
> > > + external functions on report generation; if a race report is
> > > + generated from any one of them, system stability may suffer due to
> > > + deadlocks or recursion. If in doubt, say N.
> > > +
> > > config KCSAN_DEBUG
> > > bool "Debugging of KCSAN internals"
> > >
> > > --
> > > 2.25.0.265.gbab2e86ba0-goog
> > >
> On Feb 21, 2020, at 6:10 PM, Marco Elver <[email protected]> wrote:
>
> Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports.
> Currently information about the reporting task's held locks and IRQ
> trace events are shown, if they are enabled.
This patch is no longer in today’s linux-next. I suppose that it is because Paul had sent
the initial pull request without this one that I had missed dearly.
Is there a way to get it back there?
>
> Signed-off-by: Marco Elver <[email protected]>
> Suggested-by: Qian Cai <[email protected]>
> ---
> v3:
> * Typos
> v2:
> * Rework obtaining 'current' for the "other thread" -- it now passes
> 'current' and ensures that we stall until the report was printed, so
> that the lockdep information contained in 'current' is accurate. This
> was non-trivial but testing so far leads me to conclude this now
> reliably prints the held locks for the "other thread" (please test
> more!).
> ---
> kernel/kcsan/core.c | 4 +-
> kernel/kcsan/kcsan.h | 3 ++
> kernel/kcsan/report.c | 103 +++++++++++++++++++++++++++++++++++++++++-
> lib/Kconfig.kcsan | 13 ++++++
> 4 files changed, 120 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> index e7387fec66795..065615df88eaa 100644
> --- a/kernel/kcsan/core.c
> +++ b/kernel/kcsan/core.c
> @@ -18,8 +18,8 @@
> #include "kcsan.h"
>
> static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
> -static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> -static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> +unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> +unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
> static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
>
> diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
> index 892de5120c1b6..e282f8b5749e9 100644
> --- a/kernel/kcsan/kcsan.h
> +++ b/kernel/kcsan/kcsan.h
> @@ -13,6 +13,9 @@
> /* The number of adjacent watchpoints to check. */
> #define KCSAN_CHECK_ADJACENT 1
>
> +extern unsigned int kcsan_udelay_task;
> +extern unsigned int kcsan_udelay_interrupt;
> +
> /*
> * Globally enable and disable KCSAN.
> */
> diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
> index 11c791b886f3c..7bdb515e3662f 100644
> --- a/kernel/kcsan/report.c
> +++ b/kernel/kcsan/report.c
> @@ -1,5 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0
>
> +#include <linux/debug_locks.h>
> +#include <linux/delay.h>
> #include <linux/jiffies.h>
> #include <linux/kernel.h>
> #include <linux/lockdep.h>
> @@ -31,7 +33,26 @@ static struct {
> int cpu_id;
> unsigned long stack_entries[NUM_STACK_ENTRIES];
> int num_stack_entries;
> -} other_info = { .ptr = NULL };
> +
> + /*
> + * Optionally pass @current. Typically we do not need to pass @current
> + * via @other_info since just @task_pid is sufficient. Passing @current
> + * has additional overhead.
> + *
> + * To safely pass @current, we must either use get_task_struct/
> + * put_task_struct, or stall the thread that populated @other_info.
> + *
> + * We cannot rely on get_task_struct/put_task_struct in case
> + * release_report() races with a task being released, and would have to
> + * free it in release_report(). This may result in deadlock if we want
> + * to use KCSAN on the allocators.
> + *
> + * Since we also want to reliably print held locks for
> + * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
> + * that populated @other_info until it has been consumed.
> + */
> + struct task_struct *task;
> +} other_info;
>
> /*
> * Information about reported races; used to rate limit reporting.
> @@ -245,6 +266,16 @@ static int sym_strcmp(void *addr1, void *addr2)
> return strncmp(buf1, buf2, sizeof(buf1));
> }
>
> +static void print_verbose_info(struct task_struct *task)
> +{
> + if (!task)
> + return;
> +
> + pr_err("\n");
> + debug_show_held_locks(task);
> + print_irqtrace_events(task);
> +}
> +
> /*
> * Returns true if a report was generated, false otherwise.
> */
> @@ -319,6 +350,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> other_info.num_stack_entries - other_skipnr,
> 0);
>
> + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> + print_verbose_info(other_info.task);
> +
> pr_err("\n");
> pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
> get_access_type(access_type), ptr, size,
> @@ -340,6 +374,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> 0);
>
> + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> + print_verbose_info(current);
> +
> /* Print report footer. */
> pr_err("\n");
> pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
> @@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
> spin_unlock_irqrestore(&report_lock, *flags);
> }
>
> +/*
> + * Sets @other_info.task and awaits consumption of @other_info.
> + *
> + * Precondition: report_lock is held.
> + * Postcondition: report_lock is held.
> + */
> +static void
> +set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)
> +{
> + /*
> + * We may be instrumenting a code-path where current->state is already
> + * something other than TASK_RUNNING.
> + */
> + const bool is_running = current->state == TASK_RUNNING;
> + /*
> + * To avoid deadlock in case we are in an interrupt here and this is a
> + * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
> + * timeout to ensure this works in all contexts.
> + *
> + * Await approximately the worst case delay of the reporting thread (if
> + * we are not interrupted).
> + */
> + int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
> +
> + other_info.task = current;
> + do {
> + if (is_running) {
> + /*
> + * Let lockdep know the real task is sleeping, to print
> + * the held locks (recall we turned lockdep off, so
> + * locking/unlocking @report_lock won't be recorded).
> + */
> + set_current_state(TASK_UNINTERRUPTIBLE);
> + }
> + spin_unlock_irqrestore(&report_lock, *flags);
> + /*
> + * We cannot call schedule() since we also cannot reliably
> + * determine if sleeping here is permitted -- see in_atomic().
> + */
> +
> + udelay(1);
> + spin_lock_irqsave(&report_lock, *flags);
> + if (timeout-- < 0) {
> + /*
> + * Abort. Reset other_info.task to NULL, since it
> + * appears the other thread is still going to consume
> + * it. It will result in no verbose info printed for
> + * this task.
> + */
> + other_info.task = NULL;
> + break;
> + }
> + /*
> + * If @ptr nor @current matches, then our information has been
> + * consumed and we may continue. If not, retry.
> + */
> + } while (other_info.ptr == ptr && other_info.task == current);
> + if (is_running)
> + set_current_state(TASK_RUNNING);
> +}
> +
> /*
> * Depending on the report type either sets other_info and returns false, or
> * acquires the matching other_info and returns true. If other_info is not
> @@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
> other_info.cpu_id = cpu_id;
> other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
>
> + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> + set_other_info_task_blocking(flags, ptr);
> +
> spin_unlock_irqrestore(&report_lock, *flags);
>
> /*
> diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> index 081ed2e1bf7b1..0f1447ff8f558 100644
> --- a/lib/Kconfig.kcsan
> +++ b/lib/Kconfig.kcsan
> @@ -20,6 +20,19 @@ menuconfig KCSAN
>
> if KCSAN
>
> +config KCSAN_VERBOSE
> + bool "Show verbose reports with more information about system state"
> + depends on PROVE_LOCKING
> + help
> + If enabled, reports show more information about the system state that
> + may help better analyze and debug races. This includes held locks and
> + IRQ trace events.
> +
> + While this option should generally be benign, we call into more
> + external functions on report generation; if a race report is
> + generated from any one of them, system stability may suffer due to
> + deadlocks or recursion. If in doubt, say N.
> +
> config KCSAN_DEBUG
> bool "Debugging of KCSAN internals"
>
> --
> 2.25.0.265.gbab2e86ba0-goog
>
On Mon, Apr 06, 2020 at 08:59:58AM -0400, Qian Cai wrote:
>
>
> > On Feb 21, 2020, at 6:10 PM, Marco Elver <[email protected]> wrote:
> >
> > Adds CONFIG_KCSAN_VERBOSE to optionally enable more verbose reports.
> > Currently information about the reporting task's held locks and IRQ
> > trace events are shown, if they are enabled.
>
> This patch is no longer in today’s linux-next. I suppose that it is because Paul had sent
> the initial pull request without this one that I had missed dearly.
>
> Is there a way to get it back there?
It goes back in in seven days, after -rc1 is released. The fact that
it was there last week was a mistake on my part, and I did eventually
get my hand slapped for it. ;-)
In the meantime, if it would help, I could group the KCSAN commits
on top of those in -tip to allow you to get them with one "git pull"
command.
Thanx, Paul
> > Signed-off-by: Marco Elver <[email protected]>
> > Suggested-by: Qian Cai <[email protected]>
> > ---
> > v3:
> > * Typos
> > v2:
> > * Rework obtaining 'current' for the "other thread" -- it now passes
> > 'current' and ensures that we stall until the report was printed, so
> > that the lockdep information contained in 'current' is accurate. This
> > was non-trivial but testing so far leads me to conclude this now
> > reliably prints the held locks for the "other thread" (please test
> > more!).
> > ---
> > kernel/kcsan/core.c | 4 +-
> > kernel/kcsan/kcsan.h | 3 ++
> > kernel/kcsan/report.c | 103 +++++++++++++++++++++++++++++++++++++++++-
> > lib/Kconfig.kcsan | 13 ++++++
> > 4 files changed, 120 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> > index e7387fec66795..065615df88eaa 100644
> > --- a/kernel/kcsan/core.c
> > +++ b/kernel/kcsan/core.c
> > @@ -18,8 +18,8 @@
> > #include "kcsan.h"
> >
> > static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
> > -static unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> > -static unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> > +unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
> > +unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
> > static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
> > static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
> >
> > diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
> > index 892de5120c1b6..e282f8b5749e9 100644
> > --- a/kernel/kcsan/kcsan.h
> > +++ b/kernel/kcsan/kcsan.h
> > @@ -13,6 +13,9 @@
> > /* The number of adjacent watchpoints to check. */
> > #define KCSAN_CHECK_ADJACENT 1
> >
> > +extern unsigned int kcsan_udelay_task;
> > +extern unsigned int kcsan_udelay_interrupt;
> > +
> > /*
> > * Globally enable and disable KCSAN.
> > */
> > diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
> > index 11c791b886f3c..7bdb515e3662f 100644
> > --- a/kernel/kcsan/report.c
> > +++ b/kernel/kcsan/report.c
> > @@ -1,5 +1,7 @@
> > // SPDX-License-Identifier: GPL-2.0
> >
> > +#include <linux/debug_locks.h>
> > +#include <linux/delay.h>
> > #include <linux/jiffies.h>
> > #include <linux/kernel.h>
> > #include <linux/lockdep.h>
> > @@ -31,7 +33,26 @@ static struct {
> > int cpu_id;
> > unsigned long stack_entries[NUM_STACK_ENTRIES];
> > int num_stack_entries;
> > -} other_info = { .ptr = NULL };
> > +
> > + /*
> > + * Optionally pass @current. Typically we do not need to pass @current
> > + * via @other_info since just @task_pid is sufficient. Passing @current
> > + * has additional overhead.
> > + *
> > + * To safely pass @current, we must either use get_task_struct/
> > + * put_task_struct, or stall the thread that populated @other_info.
> > + *
> > + * We cannot rely on get_task_struct/put_task_struct in case
> > + * release_report() races with a task being released, and would have to
> > + * free it in release_report(). This may result in deadlock if we want
> > + * to use KCSAN on the allocators.
> > + *
> > + * Since we also want to reliably print held locks for
> > + * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread
> > + * that populated @other_info until it has been consumed.
> > + */
> > + struct task_struct *task;
> > +} other_info;
> >
> > /*
> > * Information about reported races; used to rate limit reporting.
> > @@ -245,6 +266,16 @@ static int sym_strcmp(void *addr1, void *addr2)
> > return strncmp(buf1, buf2, sizeof(buf1));
> > }
> >
> > +static void print_verbose_info(struct task_struct *task)
> > +{
> > + if (!task)
> > + return;
> > +
> > + pr_err("\n");
> > + debug_show_held_locks(task);
> > + print_irqtrace_events(task);
> > +}
> > +
> > /*
> > * Returns true if a report was generated, false otherwise.
> > */
> > @@ -319,6 +350,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> > other_info.num_stack_entries - other_skipnr,
> > 0);
> >
> > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > + print_verbose_info(other_info.task);
> > +
> > pr_err("\n");
> > pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
> > get_access_type(access_type), ptr, size,
> > @@ -340,6 +374,9 @@ static bool print_report(const volatile void *ptr, size_t size, int access_type,
> > stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
> > 0);
> >
> > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > + print_verbose_info(current);
> > +
> > /* Print report footer. */
> > pr_err("\n");
> > pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
> > @@ -357,6 +394,67 @@ static void release_report(unsigned long *flags, enum kcsan_report_type type)
> > spin_unlock_irqrestore(&report_lock, *flags);
> > }
> >
> > +/*
> > + * Sets @other_info.task and awaits consumption of @other_info.
> > + *
> > + * Precondition: report_lock is held.
> > + * Postcondition: report_lock is held.
> > + */
> > +static void
> > +set_other_info_task_blocking(unsigned long *flags, const volatile void *ptr)
> > +{
> > + /*
> > + * We may be instrumenting a code-path where current->state is already
> > + * something other than TASK_RUNNING.
> > + */
> > + const bool is_running = current->state == TASK_RUNNING;
> > + /*
> > + * To avoid deadlock in case we are in an interrupt here and this is a
> > + * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a
> > + * timeout to ensure this works in all contexts.
> > + *
> > + * Await approximately the worst case delay of the reporting thread (if
> > + * we are not interrupted).
> > + */
> > + int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt);
> > +
> > + other_info.task = current;
> > + do {
> > + if (is_running) {
> > + /*
> > + * Let lockdep know the real task is sleeping, to print
> > + * the held locks (recall we turned lockdep off, so
> > + * locking/unlocking @report_lock won't be recorded).
> > + */
> > + set_current_state(TASK_UNINTERRUPTIBLE);
> > + }
> > + spin_unlock_irqrestore(&report_lock, *flags);
> > + /*
> > + * We cannot call schedule() since we also cannot reliably
> > + * determine if sleeping here is permitted -- see in_atomic().
> > + */
> > +
> > + udelay(1);
> > + spin_lock_irqsave(&report_lock, *flags);
> > + if (timeout-- < 0) {
> > + /*
> > + * Abort. Reset other_info.task to NULL, since it
> > + * appears the other thread is still going to consume
> > + * it. It will result in no verbose info printed for
> > + * this task.
> > + */
> > + other_info.task = NULL;
> > + break;
> > + }
> > + /*
> > + * If @ptr nor @current matches, then our information has been
> > + * consumed and we may continue. If not, retry.
> > + */
> > + } while (other_info.ptr == ptr && other_info.task == current);
> > + if (is_running)
> > + set_current_state(TASK_RUNNING);
> > +}
> > +
> > /*
> > * Depending on the report type either sets other_info and returns false, or
> > * acquires the matching other_info and returns true. If other_info is not
> > @@ -388,6 +486,9 @@ static bool prepare_report(unsigned long *flags, const volatile void *ptr,
> > other_info.cpu_id = cpu_id;
> > other_info.num_stack_entries = stack_trace_save(other_info.stack_entries, NUM_STACK_ENTRIES, 1);
> >
> > + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE))
> > + set_other_info_task_blocking(flags, ptr);
> > +
> > spin_unlock_irqrestore(&report_lock, *flags);
> >
> > /*
> > diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> > index 081ed2e1bf7b1..0f1447ff8f558 100644
> > --- a/lib/Kconfig.kcsan
> > +++ b/lib/Kconfig.kcsan
> > @@ -20,6 +20,19 @@ menuconfig KCSAN
> >
> > if KCSAN
> >
> > +config KCSAN_VERBOSE
> > + bool "Show verbose reports with more information about system state"
> > + depends on PROVE_LOCKING
> > + help
> > + If enabled, reports show more information about the system state that
> > + may help better analyze and debug races. This includes held locks and
> > + IRQ trace events.
> > +
> > + While this option should generally be benign, we call into more
> > + external functions on report generation; if a race report is
> > + generated from any one of them, system stability may suffer due to
> > + deadlocks or recursion. If in doubt, say N.
> > +
> > config KCSAN_DEBUG
> > bool "Debugging of KCSAN internals"
> >
> > --
> > 2.25.0.265.gbab2e86ba0-goog
> >
>
> On Apr 6, 2020, at 9:35 AM, Paul E. McKenney <[email protected]> wrote:
>
> It goes back in in seven days, after -rc1 is released. The fact that
> it was there last week was a mistake on my part, and I did eventually
> get my hand slapped for it. ;-)
>
> In the meantime, if it would help, I could group the KCSAN commits
> on top of those in -tip to allow you to get them with one "git pull"
> command.
Testing Linux-next for a week without that commit with KCSAN is a torture, so please do that if that is not much work. Otherwise, I could manually cherry-pick the commit myself after fixing all the offsets.
On Mon, Apr 06, 2020 at 09:45:44AM -0400, Qian Cai wrote:
>
>
> > On Apr 6, 2020, at 9:35 AM, Paul E. McKenney <[email protected]> wrote:
> >
> > It goes back in in seven days, after -rc1 is released. The fact that
> > it was there last week was a mistake on my part, and I did eventually
> > get my hand slapped for it. ;-)
> >
> > In the meantime, if it would help, I could group the KCSAN commits
> > on top of those in -tip to allow you to get them with one "git pull"
> > command.
>
> Testing Linux-next for a week without that commit with KCSAN is a torture, so please do that if that is not much work. Otherwise, I could manually cherry-pick the commit myself after fixing all the offsets.
Just to confirm, you are interested in this -rcu commit, correct?
2402d0eae589 ("kcsan: Add option for verbose reporting")
This one and the following are directly on top of the KCSAN stack
that is in -tip and thus -next:
48b1fc1 kcsan: Add option to allow watcher interruptions
2402d0e kcsan: Add option for verbose reporting
44656d3 kcsan: Add current->state to implicitly atomic accesses
e7b3410 kcsan: Fix a typo in a comment
e7325b7 kcsan: Update Documentation/dev-tools/kcsan.rst
1443b8c kcsan: Update API documentation in kcsan-checks.h
These are on top of this -tip commit:
f5d2313bd3c5 ("kcsan, trace: Make KCSAN compatible with tracing")
You can pull them in via the kcsan-dev.2020.03.25a branch if you wish.
Thanx, Paul
> On Apr 6, 2020, at 3:51 PM, Paul E. McKenney <[email protected]> wrote:
>
> On Mon, Apr 06, 2020 at 09:45:44AM -0400, Qian Cai wrote:
>>
>>
>>> On Apr 6, 2020, at 9:35 AM, Paul E. McKenney <[email protected]> wrote:
>>>
>>> It goes back in in seven days, after -rc1 is released. The fact that
>>> it was there last week was a mistake on my part, and I did eventually
>>> get my hand slapped for it. ;-)
>>>
>>> In the meantime, if it would help, I could group the KCSAN commits
>>> on top of those in -tip to allow you to get them with one "git pull"
>>> command.
>>
>> Testing Linux-next for a week without that commit with KCSAN is a torture, so please do that if that is not much work. Otherwise, I could manually cherry-pick the commit myself after fixing all the offsets.
>
> Just to confirm, you are interested in this -rcu commit, correct?
>
> 2402d0eae589 ("kcsan: Add option for verbose reporting")
>
> This one and the following are directly on top of the KCSAN stack
> that is in -tip and thus -next:
>
> 48b1fc1 kcsan: Add option to allow watcher interruptions
> 2402d0e kcsan: Add option for verbose reporting
> 44656d3 kcsan: Add current->state to implicitly atomic accesses
> e7b3410 kcsan: Fix a typo in a comment
> e7325b7 kcsan: Update Documentation/dev-tools/kcsan.rst
> 1443b8c kcsan: Update API documentation in kcsan-checks.h
>
> These are on top of this -tip commit:
>
> f5d2313bd3c5 ("kcsan, trace: Make KCSAN compatible with tracing")
>
> You can pull them in via the kcsan-dev.2020.03.25a branch if you wish.
Great! That should be enough food for me to survive for this week.
On Mon, Apr 06, 2020 at 04:33:27PM -0400, Qian Cai wrote:
>
>
> > On Apr 6, 2020, at 3:51 PM, Paul E. McKenney <[email protected]> wrote:
> >
> > On Mon, Apr 06, 2020 at 09:45:44AM -0400, Qian Cai wrote:
> >>
> >>
> >>> On Apr 6, 2020, at 9:35 AM, Paul E. McKenney <[email protected]> wrote:
> >>>
> >>> It goes back in in seven days, after -rc1 is released. The fact that
> >>> it was there last week was a mistake on my part, and I did eventually
> >>> get my hand slapped for it. ;-)
> >>>
> >>> In the meantime, if it would help, I could group the KCSAN commits
> >>> on top of those in -tip to allow you to get them with one "git pull"
> >>> command.
> >>
> >> Testing Linux-next for a week without that commit with KCSAN is a torture, so please do that if that is not much work. Otherwise, I could manually cherry-pick the commit myself after fixing all the offsets.
> >
> > Just to confirm, you are interested in this -rcu commit, correct?
> >
> > 2402d0eae589 ("kcsan: Add option for verbose reporting")
> >
> > This one and the following are directly on top of the KCSAN stack
> > that is in -tip and thus -next:
> >
> > 48b1fc1 kcsan: Add option to allow watcher interruptions
> > 2402d0e kcsan: Add option for verbose reporting
> > 44656d3 kcsan: Add current->state to implicitly atomic accesses
> > e7b3410 kcsan: Fix a typo in a comment
> > e7325b7 kcsan: Update Documentation/dev-tools/kcsan.rst
> > 1443b8c kcsan: Update API documentation in kcsan-checks.h
> >
> > These are on top of this -tip commit:
> >
> > f5d2313bd3c5 ("kcsan, trace: Make KCSAN compatible with tracing")
> >
> > You can pull them in via the kcsan-dev.2020.03.25a branch if you wish.
>
> Great! That should be enough food for me to survive for this week.
And I just put it back. Please accept my apologies for the delay, but
the branching process fought a bit harder than usual. I probably missed
today's -next, but hopefully tomorrow!
Thanx, Paul