DEBUG_LOCK_ALLOC=y is not a production setting, but it is
not very unusual either. Many developers routinely
use kernels built with it enabled.
Apart from being selected by hand, it is also auto-selected by
PROVE_LOCKING "Lock debugging: prove locking correctness" and
LOCK_STAT "Lock usage statistics" config options.
LOCK STAT is necessary for "perf lock" to work.
I wouldn't spend too much time optimizing it, but this particular
function has a very large cost in code size: when it is deinlined,
code size decreases by 830,000 bytes:
text data bss dec hex filename
85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
84837612 22294424 20627456 127759492 79d7484 vmlinux
(with this config: http://busybox.net/~vda/kernel_config)
Signed-off-by: Denys Vlasenko <[email protected]>
CC: "Paul E. McKenney" <[email protected]>
CC: Josh Triplett <[email protected]>
CC: Steven Rostedt <[email protected]>
CC: Mathieu Desnoyers <[email protected]>
CC: Lai Jiangshan <[email protected]>
CC: [email protected]
CC: Tejun Heo <[email protected]>
CC: Oleg Nesterov <[email protected]>
---
include/linux/rcupdate.h | 40 ++-----------------------------------
kernel/rcu/update.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+), 38 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 7809749..6024a65 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -439,46 +439,10 @@ int rcu_read_lock_bh_held(void);
* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
* RCU-sched read-side critical section. In absence of
* CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
- * critical section unless it can prove otherwise. Note that disabling
- * of preemption (including disabling irqs) counts as an RCU-sched
- * read-side critical section. This is useful for debug checks in functions
- * that required that they be called within an RCU-sched read-side
- * critical section.
- *
- * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
- * and while lockdep is disabled.
- *
- * Note that if the CPU is in the idle loop from an RCU point of
- * view (ie: that we are in the section between rcu_idle_enter() and
- * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
- * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
- * that are in such a section, considering these as in extended quiescent
- * state, so such a CPU is effectively never in an RCU read-side critical
- * section regardless of what RCU primitives it invokes. This state of
- * affairs is required --- we need to keep an RCU-free window in idle
- * where the CPU may possibly enter into low power mode. This way we can
- * notice an extended quiescent state to other CPUs that started a grace
- * period. Otherwise we would delay any grace period as long as we run in
- * the idle task.
- *
- * Similarly, we avoid claiming an SRCU read lock held if the current
- * CPU is offline.
+ * critical section unless it can prove otherwise.
*/
#ifdef CONFIG_PREEMPT_COUNT
-static inline int rcu_read_lock_sched_held(void)
-{
- int lockdep_opinion = 0;
-
- if (!debug_lockdep_rcu_enabled())
- return 1;
- if (!rcu_is_watching())
- return 0;
- if (!rcu_lockdep_current_cpu_online())
- return 0;
- if (debug_locks)
- lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
- return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
-}
+int rcu_read_lock_sched_held(void);
#else /* #ifdef CONFIG_PREEMPT_COUNT */
static inline int rcu_read_lock_sched_held(void)
{
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index e0d31a3..e02218f 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -62,6 +62,58 @@ MODULE_ALIAS("rcupdate");
module_param(rcu_expedited, int, 0);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+/**
+ * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
+ *
+ * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
+ * RCU-sched read-side critical section. In absence of
+ * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
+ * critical section unless it can prove otherwise. Note that disabling
+ * of preemption (including disabling irqs) counts as an RCU-sched
+ * read-side critical section. This is useful for debug checks in functions
+ * that required that they be called within an RCU-sched read-side
+ * critical section.
+ *
+ * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
+ * and while lockdep is disabled.
+ *
+ * Note that if the CPU is in the idle loop from an RCU point of
+ * view (ie: that we are in the section between rcu_idle_enter() and
+ * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
+ * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
+ * that are in such a section, considering these as in extended quiescent
+ * state, so such a CPU is effectively never in an RCU read-side critical
+ * section regardless of what RCU primitives it invokes. This state of
+ * affairs is required --- we need to keep an RCU-free window in idle
+ * where the CPU may possibly enter into low power mode. This way we can
+ * notice an extended quiescent state to other CPUs that started a grace
+ * period. Otherwise we would delay any grace period as long as we run in
+ * the idle task.
+ *
+ * Similarly, we avoid claiming an SRCU read lock held if the current
+ * CPU is offline.
+ */
+#ifdef CONFIG_PREEMPT_COUNT
+int rcu_read_lock_sched_held(void)
+{
+ int lockdep_opinion = 0;
+
+ if (!debug_lockdep_rcu_enabled())
+ return 1;
+ if (!rcu_is_watching())
+ return 0;
+ if (!rcu_lockdep_current_cpu_online())
+ return 0;
+ if (debug_locks)
+ lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
+ return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
+}
+EXPORT_SYMBOL(rcu_read_lock_sched_held);
+#else
+/* !CONFIG_PREEMPT_COUNT - the function is inlined to always return 1 */
+#endif
+
#ifdef CONFIG_PREEMPT_RCU
/*
--
1.8.1.4
On Thu, May 21, 2015 at 12:04:07PM +0200, Denys Vlasenko wrote:
> DEBUG_LOCK_ALLOC=y is not a production setting, but it is
> not very unusual either. Many developers routinely
> use kernels built with it enabled.
>
> Apart from being selected by hand, it is also auto-selected by
> PROVE_LOCKING "Lock debugging: prove locking correctness" and
> LOCK_STAT "Lock usage statistics" config options.
> LOCK STAT is necessary for "perf lock" to work.
>
> I wouldn't spend too much time optimizing it, but this particular
> function has a very large cost in code size: when it is deinlined,
> code size decreases by 830,000 bytes:
>
> text data bss dec hex filename
> 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
> 84837612 22294424 20627456 127759492 79d7484 vmlinux
>
> (with this config: http://busybox.net/~vda/kernel_config)
OK, I'll bite... I do see the numbers above, but is this really a
problem for anyone? As you say, DEBUG_LOCK_ALLOC=y is not a production
setting.
Thanx, Paul
> Signed-off-by: Denys Vlasenko <[email protected]>
> CC: "Paul E. McKenney" <[email protected]>
> CC: Josh Triplett <[email protected]>
> CC: Steven Rostedt <[email protected]>
> CC: Mathieu Desnoyers <[email protected]>
> CC: Lai Jiangshan <[email protected]>
> CC: [email protected]
> CC: Tejun Heo <[email protected]>
> CC: Oleg Nesterov <[email protected]>
> ---
> include/linux/rcupdate.h | 40 ++-----------------------------------
> kernel/rcu/update.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 54 insertions(+), 38 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 7809749..6024a65 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -439,46 +439,10 @@ int rcu_read_lock_bh_held(void);
> * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> * RCU-sched read-side critical section. In absence of
> * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> - * critical section unless it can prove otherwise. Note that disabling
> - * of preemption (including disabling irqs) counts as an RCU-sched
> - * read-side critical section. This is useful for debug checks in functions
> - * that required that they be called within an RCU-sched read-side
> - * critical section.
> - *
> - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> - * and while lockdep is disabled.
> - *
> - * Note that if the CPU is in the idle loop from an RCU point of
> - * view (ie: that we are in the section between rcu_idle_enter() and
> - * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> - * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> - * that are in such a section, considering these as in extended quiescent
> - * state, so such a CPU is effectively never in an RCU read-side critical
> - * section regardless of what RCU primitives it invokes. This state of
> - * affairs is required --- we need to keep an RCU-free window in idle
> - * where the CPU may possibly enter into low power mode. This way we can
> - * notice an extended quiescent state to other CPUs that started a grace
> - * period. Otherwise we would delay any grace period as long as we run in
> - * the idle task.
> - *
> - * Similarly, we avoid claiming an SRCU read lock held if the current
> - * CPU is offline.
> + * critical section unless it can prove otherwise.
> */
> #ifdef CONFIG_PREEMPT_COUNT
> -static inline int rcu_read_lock_sched_held(void)
> -{
> - int lockdep_opinion = 0;
> -
> - if (!debug_lockdep_rcu_enabled())
> - return 1;
> - if (!rcu_is_watching())
> - return 0;
> - if (!rcu_lockdep_current_cpu_online())
> - return 0;
> - if (debug_locks)
> - lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> - return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> -}
> +int rcu_read_lock_sched_held(void);
> #else /* #ifdef CONFIG_PREEMPT_COUNT */
> static inline int rcu_read_lock_sched_held(void)
> {
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index e0d31a3..e02218f 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -62,6 +62,58 @@ MODULE_ALIAS("rcupdate");
>
> module_param(rcu_expedited, int, 0);
>
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +/**
> + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
> + *
> + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> + * RCU-sched read-side critical section. In absence of
> + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> + * critical section unless it can prove otherwise. Note that disabling
> + * of preemption (including disabling irqs) counts as an RCU-sched
> + * read-side critical section. This is useful for debug checks in functions
> + * that required that they be called within an RCU-sched read-side
> + * critical section.
> + *
> + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> + * and while lockdep is disabled.
> + *
> + * Note that if the CPU is in the idle loop from an RCU point of
> + * view (ie: that we are in the section between rcu_idle_enter() and
> + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> + * that are in such a section, considering these as in extended quiescent
> + * state, so such a CPU is effectively never in an RCU read-side critical
> + * section regardless of what RCU primitives it invokes. This state of
> + * affairs is required --- we need to keep an RCU-free window in idle
> + * where the CPU may possibly enter into low power mode. This way we can
> + * notice an extended quiescent state to other CPUs that started a grace
> + * period. Otherwise we would delay any grace period as long as we run in
> + * the idle task.
> + *
> + * Similarly, we avoid claiming an SRCU read lock held if the current
> + * CPU is offline.
> + */
> +#ifdef CONFIG_PREEMPT_COUNT
> +int rcu_read_lock_sched_held(void)
> +{
> + int lockdep_opinion = 0;
> +
> + if (!debug_lockdep_rcu_enabled())
> + return 1;
> + if (!rcu_is_watching())
> + return 0;
> + if (!rcu_lockdep_current_cpu_online())
> + return 0;
> + if (debug_locks)
> + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> + return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> +}
> +EXPORT_SYMBOL(rcu_read_lock_sched_held);
> +#else
> +/* !CONFIG_PREEMPT_COUNT - the function is inlined to always return 1 */
> +#endif
> +
> #ifdef CONFIG_PREEMPT_RCU
>
> /*
> --
> 1.8.1.4
>
On Thu, 21 May 2015 05:52:24 -0700
"Paul E. McKenney" <[email protected]> wrote:
> On Thu, May 21, 2015 at 12:04:07PM +0200, Denys Vlasenko wrote:
> > DEBUG_LOCK_ALLOC=y is not a production setting, but it is
> > not very unusual either. Many developers routinely
> > use kernels built with it enabled.
> >
> > Apart from being selected by hand, it is also auto-selected by
> > PROVE_LOCKING "Lock debugging: prove locking correctness" and
> > LOCK_STAT "Lock usage statistics" config options.
> > LOCK STAT is necessary for "perf lock" to work.
> >
> > I wouldn't spend too much time optimizing it, but this particular
> > function has a very large cost in code size: when it is deinlined,
> > code size decreases by 830,000 bytes:
> >
> > text data bss dec hex filename
> > 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
> > 84837612 22294424 20627456 127759492 79d7484 vmlinux
> >
> > (with this config: http://busybox.net/~vda/kernel_config)
>
> OK, I'll bite... I do see the numbers above, but is this really a
> problem for anyone? As you say, DEBUG_LOCK_ALLOC=y is not a production
> setting.
>
Correct, and because it's not a production setting it should be fine as
a call and not a static inline. The i$ hit probably neglects the saving
of it being inlined too.
It's not a big deal either way, but it may make building the kernel a
bit faster ;-)
-- Steve
On Thu, May 21, 2015 at 09:09:43AM -0400, Steven Rostedt wrote:
> On Thu, 21 May 2015 05:52:24 -0700
> "Paul E. McKenney" <[email protected]> wrote:
>
> > On Thu, May 21, 2015 at 12:04:07PM +0200, Denys Vlasenko wrote:
> > > DEBUG_LOCK_ALLOC=y is not a production setting, but it is
> > > not very unusual either. Many developers routinely
> > > use kernels built with it enabled.
> > >
> > > Apart from being selected by hand, it is also auto-selected by
> > > PROVE_LOCKING "Lock debugging: prove locking correctness" and
> > > LOCK_STAT "Lock usage statistics" config options.
> > > LOCK STAT is necessary for "perf lock" to work.
> > >
> > > I wouldn't spend too much time optimizing it, but this particular
> > > function has a very large cost in code size: when it is deinlined,
> > > code size decreases by 830,000 bytes:
> > >
> > > text data bss dec hex filename
> > > 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
> > > 84837612 22294424 20627456 127759492 79d7484 vmlinux
> > >
> > > (with this config: http://busybox.net/~vda/kernel_config)
> >
> > OK, I'll bite... I do see the numbers above, but is this really a
> > problem for anyone? As you say, DEBUG_LOCK_ALLOC=y is not a production
> > setting.
> >
>
> Correct, and because it's not a production setting it should be fine as
> a call and not a static inline. The i$ hit probably neglects the saving
> of it being inlined too.
>
> It's not a big deal either way, but it may make building the kernel a
> bit faster ;-)
OK, if you believe that it is valuable enough to give it a Reviewed-by,
I will queue it. ;-)
Thanx, Paul
On Thu, 21 May 2015 06:25:28 -0700
"Paul E. McKenney" <[email protected]> wrote:
> OK, if you believe that it is valuable enough to give it a Reviewed-by,
> I will queue it. ;-)
Let me take a closer look at the patch first.
-- Steve
On Thu, 21 May 2015 12:04:07 +0200
Denys Vlasenko <[email protected]> wrote:
> DEBUG_LOCK_ALLOC=y is not a production setting, but it is
> not very unusual either. Many developers routinely
> use kernels built with it enabled.
>
> Apart from being selected by hand, it is also auto-selected by
> PROVE_LOCKING "Lock debugging: prove locking correctness" and
> LOCK_STAT "Lock usage statistics" config options.
> LOCK STAT is necessary for "perf lock" to work.
>
> I wouldn't spend too much time optimizing it, but this particular
> function has a very large cost in code size: when it is deinlined,
> code size decreases by 830,000 bytes:
>
> text data bss dec hex filename
> 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
> 84837612 22294424 20627456 127759492 79d7484 vmlinux
>
> (with this config: http://busybox.net/~vda/kernel_config)
>
> Signed-off-by: Denys Vlasenko <[email protected]>
> CC: "Paul E. McKenney" <[email protected]>
> CC: Josh Triplett <[email protected]>
> CC: Steven Rostedt <[email protected]>
> CC: Mathieu Desnoyers <[email protected]>
> CC: Lai Jiangshan <[email protected]>
> CC: [email protected]
> CC: Tejun Heo <[email protected]>
> CC: Oleg Nesterov <[email protected]>
> ---
> include/linux/rcupdate.h | 40 ++-----------------------------------
> kernel/rcu/update.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 54 insertions(+), 38 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 7809749..6024a65 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -439,46 +439,10 @@ int rcu_read_lock_bh_held(void);
> * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> * RCU-sched read-side critical section. In absence of
> * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> - * critical section unless it can prove otherwise. Note that disabling
> - * of preemption (including disabling irqs) counts as an RCU-sched
> - * read-side critical section. This is useful for debug checks in functions
> - * that required that they be called within an RCU-sched read-side
> - * critical section.
> - *
> - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> - * and while lockdep is disabled.
> - *
> - * Note that if the CPU is in the idle loop from an RCU point of
> - * view (ie: that we are in the section between rcu_idle_enter() and
> - * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> - * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> - * that are in such a section, considering these as in extended quiescent
> - * state, so such a CPU is effectively never in an RCU read-side critical
> - * section regardless of what RCU primitives it invokes. This state of
> - * affairs is required --- we need to keep an RCU-free window in idle
> - * where the CPU may possibly enter into low power mode. This way we can
> - * notice an extended quiescent state to other CPUs that started a grace
> - * period. Otherwise we would delay any grace period as long as we run in
> - * the idle task.
> - *
> - * Similarly, we avoid claiming an SRCU read lock held if the current
> - * CPU is offline.
> + * critical section unless it can prove otherwise.
> */
> #ifdef CONFIG_PREEMPT_COUNT
> -static inline int rcu_read_lock_sched_held(void)
> -{
> - int lockdep_opinion = 0;
> -
> - if (!debug_lockdep_rcu_enabled())
> - return 1;
> - if (!rcu_is_watching())
> - return 0;
> - if (!rcu_lockdep_current_cpu_online())
> - return 0;
> - if (debug_locks)
> - lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> - return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> -}
> +int rcu_read_lock_sched_held(void);
> #else /* #ifdef CONFIG_PREEMPT_COUNT */
> static inline int rcu_read_lock_sched_held(void)
> {
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index e0d31a3..e02218f 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -62,6 +62,58 @@ MODULE_ALIAS("rcupdate");
>
> module_param(rcu_expedited, int, 0);
>
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +/**
> + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
> + *
> + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> + * RCU-sched read-side critical section. In absence of
> + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> + * critical section unless it can prove otherwise. Note that disabling
> + * of preemption (including disabling irqs) counts as an RCU-sched
> + * read-side critical section. This is useful for debug checks in functions
> + * that required that they be called within an RCU-sched read-side
> + * critical section.
> + *
> + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> + * and while lockdep is disabled.
> + *
> + * Note that if the CPU is in the idle loop from an RCU point of
> + * view (ie: that we are in the section between rcu_idle_enter() and
> + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> + * that are in such a section, considering these as in extended quiescent
> + * state, so such a CPU is effectively never in an RCU read-side critical
> + * section regardless of what RCU primitives it invokes. This state of
> + * affairs is required --- we need to keep an RCU-free window in idle
> + * where the CPU may possibly enter into low power mode. This way we can
> + * notice an extended quiescent state to other CPUs that started a grace
> + * period. Otherwise we would delay any grace period as long as we run in
> + * the idle task.
> + *
> + * Similarly, we avoid claiming an SRCU read lock held if the current
> + * CPU is offline.
> + */
> +#ifdef CONFIG_PREEMPT_COUNT
> +int rcu_read_lock_sched_held(void)
> +{
> + int lockdep_opinion = 0;
> +
> + if (!debug_lockdep_rcu_enabled())
> + return 1;
> + if (!rcu_is_watching())
> + return 0;
> + if (!rcu_lockdep_current_cpu_online())
> + return 0;
> + if (debug_locks)
> + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> + return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> +}
> +EXPORT_SYMBOL(rcu_read_lock_sched_held);
> +#else
> +/* !CONFIG_PREEMPT_COUNT - the function is inlined to always return 1 */
Nuke the #else. It's not needed and this is a common enough practice to
have the static inline foo() { } when disabled that we do not need to
comment about it here.
> +#endif
Hmm, you added two #ifdef, and one #endif. How does this even compile??
-- Steve
> +
> #ifdef CONFIG_PREEMPT_RCU
>
> /*
On 05/21/2015 03:45 PM, Steven Rostedt wrote:
> On Thu, 21 May 2015 12:04:07 +0200
> Denys Vlasenko <[email protected]> wrote:
>
>> DEBUG_LOCK_ALLOC=y is not a production setting, but it is
>> not very unusual either. Many developers routinely
>> use kernels built with it enabled.
>>
>> Apart from being selected by hand, it is also auto-selected by
>> PROVE_LOCKING "Lock debugging: prove locking correctness" and
>> LOCK_STAT "Lock usage statistics" config options.
>> LOCK STAT is necessary for "perf lock" to work.
>>
>> I wouldn't spend too much time optimizing it, but this particular
>> function has a very large cost in code size: when it is deinlined,
>> code size decreases by 830,000 bytes:
>>
>> text data bss dec hex filename
>> 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
>> 84837612 22294424 20627456 127759492 79d7484 vmlinux
>>
>> (with this config: http://busybox.net/~vda/kernel_config)
>>
>> Signed-off-by: Denys Vlasenko <[email protected]>
>> CC: "Paul E. McKenney" <[email protected]>
>> CC: Josh Triplett <[email protected]>
>> CC: Steven Rostedt <[email protected]>
>> CC: Mathieu Desnoyers <[email protected]>
>> CC: Lai Jiangshan <[email protected]>
>> CC: [email protected]
>> CC: Tejun Heo <[email protected]>
>> CC: Oleg Nesterov <[email protected]>
>> ---
>> include/linux/rcupdate.h | 40 ++-----------------------------------
>> kernel/rcu/update.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 54 insertions(+), 38 deletions(-)
>>
>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
>> index 7809749..6024a65 100644
>> --- a/include/linux/rcupdate.h
>> +++ b/include/linux/rcupdate.h
>> @@ -439,46 +439,10 @@ int rcu_read_lock_bh_held(void);
>> * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
>> * RCU-sched read-side critical section. In absence of
>> * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
>> - * critical section unless it can prove otherwise. Note that disabling
>> - * of preemption (including disabling irqs) counts as an RCU-sched
>> - * read-side critical section. This is useful for debug checks in functions
>> - * that required that they be called within an RCU-sched read-side
>> - * critical section.
>> - *
>> - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
>> - * and while lockdep is disabled.
>> - *
>> - * Note that if the CPU is in the idle loop from an RCU point of
>> - * view (ie: that we are in the section between rcu_idle_enter() and
>> - * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
>> - * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
>> - * that are in such a section, considering these as in extended quiescent
>> - * state, so such a CPU is effectively never in an RCU read-side critical
>> - * section regardless of what RCU primitives it invokes. This state of
>> - * affairs is required --- we need to keep an RCU-free window in idle
>> - * where the CPU may possibly enter into low power mode. This way we can
>> - * notice an extended quiescent state to other CPUs that started a grace
>> - * period. Otherwise we would delay any grace period as long as we run in
>> - * the idle task.
>> - *
>> - * Similarly, we avoid claiming an SRCU read lock held if the current
>> - * CPU is offline.
>> + * critical section unless it can prove otherwise.
>> */
>> #ifdef CONFIG_PREEMPT_COUNT
>> -static inline int rcu_read_lock_sched_held(void)
>> -{
>> - int lockdep_opinion = 0;
>> -
>> - if (!debug_lockdep_rcu_enabled())
>> - return 1;
>> - if (!rcu_is_watching())
>> - return 0;
>> - if (!rcu_lockdep_current_cpu_online())
>> - return 0;
>> - if (debug_locks)
>> - lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
>> - return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
>> -}
>> +int rcu_read_lock_sched_held(void);
>> #else /* #ifdef CONFIG_PREEMPT_COUNT */
>> static inline int rcu_read_lock_sched_held(void)
>> {
>> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
>> index e0d31a3..e02218f 100644
>> --- a/kernel/rcu/update.c
>> +++ b/kernel/rcu/update.c
>> @@ -62,6 +62,58 @@ MODULE_ALIAS("rcupdate");
>>
>> module_param(rcu_expedited, int, 0);
>>
>> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
>> +/**
>> + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
>> + *
>> + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
>> + * RCU-sched read-side critical section. In absence of
>> + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
>> + * critical section unless it can prove otherwise. Note that disabling
>> + * of preemption (including disabling irqs) counts as an RCU-sched
>> + * read-side critical section. This is useful for debug checks in functions
>> + * that required that they be called within an RCU-sched read-side
>> + * critical section.
>> + *
>> + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
>> + * and while lockdep is disabled.
>> + *
>> + * Note that if the CPU is in the idle loop from an RCU point of
>> + * view (ie: that we are in the section between rcu_idle_enter() and
>> + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
>> + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
>> + * that are in such a section, considering these as in extended quiescent
>> + * state, so such a CPU is effectively never in an RCU read-side critical
>> + * section regardless of what RCU primitives it invokes. This state of
>> + * affairs is required --- we need to keep an RCU-free window in idle
>> + * where the CPU may possibly enter into low power mode. This way we can
>> + * notice an extended quiescent state to other CPUs that started a grace
>> + * period. Otherwise we would delay any grace period as long as we run in
>> + * the idle task.
>> + *
>> + * Similarly, we avoid claiming an SRCU read lock held if the current
>> + * CPU is offline.
>> + */
>> +#ifdef CONFIG_PREEMPT_COUNT
>> +int rcu_read_lock_sched_held(void)
>> +{
>> + int lockdep_opinion = 0;
>> +
>> + if (!debug_lockdep_rcu_enabled())
>> + return 1;
>> + if (!rcu_is_watching())
>> + return 0;
>> + if (!rcu_lockdep_current_cpu_online())
>> + return 0;
>> + if (debug_locks)
>> + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
>> + return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
>> +}
>> +EXPORT_SYMBOL(rcu_read_lock_sched_held);
>> +#else
>> +/* !CONFIG_PREEMPT_COUNT - the function is inlined to always return 1 */
>
> Nuke the #else. It's not needed and this is a common enough practice to
> have the static inline foo() { } when disabled that we do not need to
> comment about it here.
Sending patch v2 in a few minutes.
>> +#endif
>
> Hmm, you added two #ifdef, and one #endif. How does this even compile??
Er... it... doesn't.
There was "#if defined CONFIG_DEBUG_LOCK_ALLOC && defined CONFIG_PREEMPT_COUNT"
but then I split it into two #ifs to have a nice explanatory empty
#else clause. And I did not test it after that edit
("what could possibly go wrong?"). Sorry.
Patch v2 I'm sending _is_ tested.
On Thu, May 21, 2015 at 05:09:27PM +0200, Denys Vlasenko wrote:
> On 05/21/2015 03:45 PM, Steven Rostedt wrote:
> > On Thu, 21 May 2015 12:04:07 +0200
> > Denys Vlasenko <[email protected]> wrote:
> >
> >> DEBUG_LOCK_ALLOC=y is not a production setting, but it is
> >> not very unusual either. Many developers routinely
> >> use kernels built with it enabled.
> >>
> >> Apart from being selected by hand, it is also auto-selected by
> >> PROVE_LOCKING "Lock debugging: prove locking correctness" and
> >> LOCK_STAT "Lock usage statistics" config options.
> >> LOCK STAT is necessary for "perf lock" to work.
> >>
> >> I wouldn't spend too much time optimizing it, but this particular
> >> function has a very large cost in code size: when it is deinlined,
> >> code size decreases by 830,000 bytes:
> >>
> >> text data bss dec hex filename
> >> 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
> >> 84837612 22294424 20627456 127759492 79d7484 vmlinux
> >>
> >> (with this config: http://busybox.net/~vda/kernel_config)
> >>
> >> Signed-off-by: Denys Vlasenko <[email protected]>
> >> CC: "Paul E. McKenney" <[email protected]>
> >> CC: Josh Triplett <[email protected]>
> >> CC: Steven Rostedt <[email protected]>
> >> CC: Mathieu Desnoyers <[email protected]>
> >> CC: Lai Jiangshan <[email protected]>
> >> CC: [email protected]
> >> CC: Tejun Heo <[email protected]>
> >> CC: Oleg Nesterov <[email protected]>
> >> ---
> >> include/linux/rcupdate.h | 40 ++-----------------------------------
> >> kernel/rcu/update.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
> >> 2 files changed, 54 insertions(+), 38 deletions(-)
> >>
> >> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> >> index 7809749..6024a65 100644
> >> --- a/include/linux/rcupdate.h
> >> +++ b/include/linux/rcupdate.h
> >> @@ -439,46 +439,10 @@ int rcu_read_lock_bh_held(void);
> >> * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> >> * RCU-sched read-side critical section. In absence of
> >> * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> >> - * critical section unless it can prove otherwise. Note that disabling
> >> - * of preemption (including disabling irqs) counts as an RCU-sched
> >> - * read-side critical section. This is useful for debug checks in functions
> >> - * that required that they be called within an RCU-sched read-side
> >> - * critical section.
> >> - *
> >> - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> >> - * and while lockdep is disabled.
> >> - *
> >> - * Note that if the CPU is in the idle loop from an RCU point of
> >> - * view (ie: that we are in the section between rcu_idle_enter() and
> >> - * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> >> - * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> >> - * that are in such a section, considering these as in extended quiescent
> >> - * state, so such a CPU is effectively never in an RCU read-side critical
> >> - * section regardless of what RCU primitives it invokes. This state of
> >> - * affairs is required --- we need to keep an RCU-free window in idle
> >> - * where the CPU may possibly enter into low power mode. This way we can
> >> - * notice an extended quiescent state to other CPUs that started a grace
> >> - * period. Otherwise we would delay any grace period as long as we run in
> >> - * the idle task.
> >> - *
> >> - * Similarly, we avoid claiming an SRCU read lock held if the current
> >> - * CPU is offline.
> >> + * critical section unless it can prove otherwise.
> >> */
> >> #ifdef CONFIG_PREEMPT_COUNT
> >> -static inline int rcu_read_lock_sched_held(void)
> >> -{
> >> - int lockdep_opinion = 0;
> >> -
> >> - if (!debug_lockdep_rcu_enabled())
> >> - return 1;
> >> - if (!rcu_is_watching())
> >> - return 0;
> >> - if (!rcu_lockdep_current_cpu_online())
> >> - return 0;
> >> - if (debug_locks)
> >> - lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> >> - return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> >> -}
> >> +int rcu_read_lock_sched_held(void);
> >> #else /* #ifdef CONFIG_PREEMPT_COUNT */
> >> static inline int rcu_read_lock_sched_held(void)
> >> {
> >> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> >> index e0d31a3..e02218f 100644
> >> --- a/kernel/rcu/update.c
> >> +++ b/kernel/rcu/update.c
> >> @@ -62,6 +62,58 @@ MODULE_ALIAS("rcupdate");
> >>
> >> module_param(rcu_expedited, int, 0);
> >>
> >> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> >> +/**
> >> + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
> >> + *
> >> + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> >> + * RCU-sched read-side critical section. In absence of
> >> + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> >> + * critical section unless it can prove otherwise. Note that disabling
> >> + * of preemption (including disabling irqs) counts as an RCU-sched
> >> + * read-side critical section. This is useful for debug checks in functions
> >> + * that required that they be called within an RCU-sched read-side
> >> + * critical section.
> >> + *
> >> + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> >> + * and while lockdep is disabled.
> >> + *
> >> + * Note that if the CPU is in the idle loop from an RCU point of
> >> + * view (ie: that we are in the section between rcu_idle_enter() and
> >> + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> >> + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> >> + * that are in such a section, considering these as in extended quiescent
> >> + * state, so such a CPU is effectively never in an RCU read-side critical
> >> + * section regardless of what RCU primitives it invokes. This state of
> >> + * affairs is required --- we need to keep an RCU-free window in idle
> >> + * where the CPU may possibly enter into low power mode. This way we can
> >> + * notice an extended quiescent state to other CPUs that started a grace
> >> + * period. Otherwise we would delay any grace period as long as we run in
> >> + * the idle task.
> >> + *
> >> + * Similarly, we avoid claiming an SRCU read lock held if the current
> >> + * CPU is offline.
> >> + */
> >> +#ifdef CONFIG_PREEMPT_COUNT
> >> +int rcu_read_lock_sched_held(void)
> >> +{
> >> + int lockdep_opinion = 0;
> >> +
> >> + if (!debug_lockdep_rcu_enabled())
> >> + return 1;
> >> + if (!rcu_is_watching())
> >> + return 0;
> >> + if (!rcu_lockdep_current_cpu_online())
> >> + return 0;
> >> + if (debug_locks)
> >> + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> >> + return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> >> +}
> >> +EXPORT_SYMBOL(rcu_read_lock_sched_held);
> >> +#else
> >> +/* !CONFIG_PREEMPT_COUNT - the function is inlined to always return 1 */
> >
> > Nuke the #else. It's not needed and this is a common enough practice to
> > have the static inline foo() { } when disabled that we do not need to
> > comment about it here.
>
> Sending patch v2 in a few minutes.
>
> >> +#endif
> >
> > Hmm, you added two #ifdef, and one #endif. How does this even compile??
>
> Er... it... doesn't.
>
> There was "#if defined CONFIG_DEBUG_LOCK_ALLOC && defined CONFIG_PREEMPT_COUNT"
> but then I split it into two #ifs to have a nice explanatory empty
> #else clause. And I did not test it after that edit
> ("what could possibly go wrong?"). Sorry.
>
> Patch v2 I'm sending _is_ tested.
Boot/run as well as build?
Thanx, Paul
On 05/21/2015 05:26 PM, Paul E. McKenney wrote:
> On Thu, May 21, 2015 at 05:09:27PM +0200, Denys Vlasenko wrote:
>> On 05/21/2015 03:45 PM, Steven Rostedt wrote:
>>> On Thu, 21 May 2015 12:04:07 +0200
>>> Denys Vlasenko <[email protected]> wrote:
>>>
>>>> DEBUG_LOCK_ALLOC=y is not a production setting, but it is
>>>> not very unusual either. Many developers routinely
>>>> use kernels built with it enabled.
>>>>
>>>> Apart from being selected by hand, it is also auto-selected by
>>>> PROVE_LOCKING "Lock debugging: prove locking correctness" and
>>>> LOCK_STAT "Lock usage statistics" config options.
>>>> LOCK STAT is necessary for "perf lock" to work.
>>>>
>>>> I wouldn't spend too much time optimizing it, but this particular
>>>> function has a very large cost in code size: when it is deinlined,
>>>> code size decreases by 830,000 bytes:
>>>>
>>>> text data bss dec hex filename
>>>> 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
>>>> 84837612 22294424 20627456 127759492 79d7484 vmlinux
>>>>
>>>> (with this config: http://busybox.net/~vda/kernel_config)
>>>>
>>>> Signed-off-by: Denys Vlasenko <[email protected]>
>>>> CC: "Paul E. McKenney" <[email protected]>
>>>> CC: Josh Triplett <[email protected]>
>>>> CC: Steven Rostedt <[email protected]>
>>>> CC: Mathieu Desnoyers <[email protected]>
>>>> CC: Lai Jiangshan <[email protected]>
>>>> CC: [email protected]
>>>> CC: Tejun Heo <[email protected]>
>>>> CC: Oleg Nesterov <[email protected]>
>>>> ---
>>>> include/linux/rcupdate.h | 40 ++-----------------------------------
>>>> kernel/rcu/update.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
>>>> 2 files changed, 54 insertions(+), 38 deletions(-)
>>>>
>>>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
>>>> index 7809749..6024a65 100644
>>>> --- a/include/linux/rcupdate.h
>>>> +++ b/include/linux/rcupdate.h
>>>> @@ -439,46 +439,10 @@ int rcu_read_lock_bh_held(void);
>>>> * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
>>>> * RCU-sched read-side critical section. In absence of
>>>> * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
>>>> - * critical section unless it can prove otherwise. Note that disabling
>>>> - * of preemption (including disabling irqs) counts as an RCU-sched
>>>> - * read-side critical section. This is useful for debug checks in functions
>>>> - * that required that they be called within an RCU-sched read-side
>>>> - * critical section.
>>>> - *
>>>> - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
>>>> - * and while lockdep is disabled.
>>>> - *
>>>> - * Note that if the CPU is in the idle loop from an RCU point of
>>>> - * view (ie: that we are in the section between rcu_idle_enter() and
>>>> - * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
>>>> - * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
>>>> - * that are in such a section, considering these as in extended quiescent
>>>> - * state, so such a CPU is effectively never in an RCU read-side critical
>>>> - * section regardless of what RCU primitives it invokes. This state of
>>>> - * affairs is required --- we need to keep an RCU-free window in idle
>>>> - * where the CPU may possibly enter into low power mode. This way we can
>>>> - * notice an extended quiescent state to other CPUs that started a grace
>>>> - * period. Otherwise we would delay any grace period as long as we run in
>>>> - * the idle task.
>>>> - *
>>>> - * Similarly, we avoid claiming an SRCU read lock held if the current
>>>> - * CPU is offline.
>>>> + * critical section unless it can prove otherwise.
>>>> */
>>>> #ifdef CONFIG_PREEMPT_COUNT
>>>> -static inline int rcu_read_lock_sched_held(void)
>>>> -{
>>>> - int lockdep_opinion = 0;
>>>> -
>>>> - if (!debug_lockdep_rcu_enabled())
>>>> - return 1;
>>>> - if (!rcu_is_watching())
>>>> - return 0;
>>>> - if (!rcu_lockdep_current_cpu_online())
>>>> - return 0;
>>>> - if (debug_locks)
>>>> - lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
>>>> - return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
>>>> -}
>>>> +int rcu_read_lock_sched_held(void);
>>>> #else /* #ifdef CONFIG_PREEMPT_COUNT */
>>>> static inline int rcu_read_lock_sched_held(void)
>>>> {
>>>> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
>>>> index e0d31a3..e02218f 100644
>>>> --- a/kernel/rcu/update.c
>>>> +++ b/kernel/rcu/update.c
>>>> @@ -62,6 +62,58 @@ MODULE_ALIAS("rcupdate");
>>>>
>>>> module_param(rcu_expedited, int, 0);
>>>>
>>>> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
>>>> +/**
>>>> + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
>>>> + *
>>>> + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
>>>> + * RCU-sched read-side critical section. In absence of
>>>> + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
>>>> + * critical section unless it can prove otherwise. Note that disabling
>>>> + * of preemption (including disabling irqs) counts as an RCU-sched
>>>> + * read-side critical section. This is useful for debug checks in functions
>>>> + * that required that they be called within an RCU-sched read-side
>>>> + * critical section.
>>>> + *
>>>> + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
>>>> + * and while lockdep is disabled.
>>>> + *
>>>> + * Note that if the CPU is in the idle loop from an RCU point of
>>>> + * view (ie: that we are in the section between rcu_idle_enter() and
>>>> + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
>>>> + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
>>>> + * that are in such a section, considering these as in extended quiescent
>>>> + * state, so such a CPU is effectively never in an RCU read-side critical
>>>> + * section regardless of what RCU primitives it invokes. This state of
>>>> + * affairs is required --- we need to keep an RCU-free window in idle
>>>> + * where the CPU may possibly enter into low power mode. This way we can
>>>> + * notice an extended quiescent state to other CPUs that started a grace
>>>> + * period. Otherwise we would delay any grace period as long as we run in
>>>> + * the idle task.
>>>> + *
>>>> + * Similarly, we avoid claiming an SRCU read lock held if the current
>>>> + * CPU is offline.
>>>> + */
>>>> +#ifdef CONFIG_PREEMPT_COUNT
>>>> +int rcu_read_lock_sched_held(void)
>>>> +{
>>>> + int lockdep_opinion = 0;
>>>> +
>>>> + if (!debug_lockdep_rcu_enabled())
>>>> + return 1;
>>>> + if (!rcu_is_watching())
>>>> + return 0;
>>>> + if (!rcu_lockdep_current_cpu_online())
>>>> + return 0;
>>>> + if (debug_locks)
>>>> + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
>>>> + return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
>>>> +}
>>>> +EXPORT_SYMBOL(rcu_read_lock_sched_held);
>>>> +#else
>>>> +/* !CONFIG_PREEMPT_COUNT - the function is inlined to always return 1 */
>>>
>>> Nuke the #else. It's not needed and this is a common enough practice to
>>> have the static inline foo() { } when disabled that we do not need to
>>> comment about it here.
>>
>> Sending patch v2 in a few minutes.
>>
>>>> +#endif
>>>
>>> Hmm, you added two #ifdef, and one #endif. How does this even compile??
>>
>> Er... it... doesn't.
>>
>> There was "#if defined CONFIG_DEBUG_LOCK_ALLOC && defined CONFIG_PREEMPT_COUNT"
>> but then I split it into two #ifs to have a nice explanatory empty
>> #else clause. And I did not test it after that edit
>> ("what could possibly go wrong?"). Sorry.
>>
>> Patch v2 I'm sending _is_ tested.
>
> Boot/run as well as build?
I did not even dare to try booting 128 megabyte allyesconfig monstrosity,
before you asked.
It took me 4 hours of rebuilds to figure out that CONFIG_CMDLINE_BOOL needs to be
disabled for my qemu boot to succeed :) :)
So, yes, patched allyesconfig kernel seems to boot... it takes 250 seconds in qemu.
On Thu, May 21, 2015 at 11:53:21PM +0200, Denys Vlasenko wrote:
> On 05/21/2015 05:26 PM, Paul E. McKenney wrote:
> > On Thu, May 21, 2015 at 05:09:27PM +0200, Denys Vlasenko wrote:
> >> On 05/21/2015 03:45 PM, Steven Rostedt wrote:
> >>> On Thu, 21 May 2015 12:04:07 +0200
> >>> Denys Vlasenko <[email protected]> wrote:
> >>>
> >>>> DEBUG_LOCK_ALLOC=y is not a production setting, but it is
> >>>> not very unusual either. Many developers routinely
> >>>> use kernels built with it enabled.
> >>>>
> >>>> Apart from being selected by hand, it is also auto-selected by
> >>>> PROVE_LOCKING "Lock debugging: prove locking correctness" and
> >>>> LOCK_STAT "Lock usage statistics" config options.
> >>>> LOCK STAT is necessary for "perf lock" to work.
> >>>>
> >>>> I wouldn't spend too much time optimizing it, but this particular
> >>>> function has a very large cost in code size: when it is deinlined,
> >>>> code size decreases by 830,000 bytes:
> >>>>
> >>>> text data bss dec hex filename
> >>>> 85674192 22294776 20627456 128596424 7aa39c8 vmlinux.before
> >>>> 84837612 22294424 20627456 127759492 79d7484 vmlinux
> >>>>
> >>>> (with this config: http://busybox.net/~vda/kernel_config)
> >>>>
> >>>> Signed-off-by: Denys Vlasenko <[email protected]>
> >>>> CC: "Paul E. McKenney" <[email protected]>
> >>>> CC: Josh Triplett <[email protected]>
> >>>> CC: Steven Rostedt <[email protected]>
> >>>> CC: Mathieu Desnoyers <[email protected]>
> >>>> CC: Lai Jiangshan <[email protected]>
> >>>> CC: [email protected]
> >>>> CC: Tejun Heo <[email protected]>
> >>>> CC: Oleg Nesterov <[email protected]>
> >>>> ---
> >>>> include/linux/rcupdate.h | 40 ++-----------------------------------
> >>>> kernel/rcu/update.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++
> >>>> 2 files changed, 54 insertions(+), 38 deletions(-)
> >>>>
> >>>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> >>>> index 7809749..6024a65 100644
> >>>> --- a/include/linux/rcupdate.h
> >>>> +++ b/include/linux/rcupdate.h
> >>>> @@ -439,46 +439,10 @@ int rcu_read_lock_bh_held(void);
> >>>> * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> >>>> * RCU-sched read-side critical section. In absence of
> >>>> * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> >>>> - * critical section unless it can prove otherwise. Note that disabling
> >>>> - * of preemption (including disabling irqs) counts as an RCU-sched
> >>>> - * read-side critical section. This is useful for debug checks in functions
> >>>> - * that required that they be called within an RCU-sched read-side
> >>>> - * critical section.
> >>>> - *
> >>>> - * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> >>>> - * and while lockdep is disabled.
> >>>> - *
> >>>> - * Note that if the CPU is in the idle loop from an RCU point of
> >>>> - * view (ie: that we are in the section between rcu_idle_enter() and
> >>>> - * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> >>>> - * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> >>>> - * that are in such a section, considering these as in extended quiescent
> >>>> - * state, so such a CPU is effectively never in an RCU read-side critical
> >>>> - * section regardless of what RCU primitives it invokes. This state of
> >>>> - * affairs is required --- we need to keep an RCU-free window in idle
> >>>> - * where the CPU may possibly enter into low power mode. This way we can
> >>>> - * notice an extended quiescent state to other CPUs that started a grace
> >>>> - * period. Otherwise we would delay any grace period as long as we run in
> >>>> - * the idle task.
> >>>> - *
> >>>> - * Similarly, we avoid claiming an SRCU read lock held if the current
> >>>> - * CPU is offline.
> >>>> + * critical section unless it can prove otherwise.
> >>>> */
> >>>> #ifdef CONFIG_PREEMPT_COUNT
> >>>> -static inline int rcu_read_lock_sched_held(void)
> >>>> -{
> >>>> - int lockdep_opinion = 0;
> >>>> -
> >>>> - if (!debug_lockdep_rcu_enabled())
> >>>> - return 1;
> >>>> - if (!rcu_is_watching())
> >>>> - return 0;
> >>>> - if (!rcu_lockdep_current_cpu_online())
> >>>> - return 0;
> >>>> - if (debug_locks)
> >>>> - lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> >>>> - return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> >>>> -}
> >>>> +int rcu_read_lock_sched_held(void);
> >>>> #else /* #ifdef CONFIG_PREEMPT_COUNT */
> >>>> static inline int rcu_read_lock_sched_held(void)
> >>>> {
> >>>> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> >>>> index e0d31a3..e02218f 100644
> >>>> --- a/kernel/rcu/update.c
> >>>> +++ b/kernel/rcu/update.c
> >>>> @@ -62,6 +62,58 @@ MODULE_ALIAS("rcupdate");
> >>>>
> >>>> module_param(rcu_expedited, int, 0);
> >>>>
> >>>> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> >>>> +/**
> >>>> + * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
> >>>> + *
> >>>> + * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
> >>>> + * RCU-sched read-side critical section. In absence of
> >>>> + * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
> >>>> + * critical section unless it can prove otherwise. Note that disabling
> >>>> + * of preemption (including disabling irqs) counts as an RCU-sched
> >>>> + * read-side critical section. This is useful for debug checks in functions
> >>>> + * that required that they be called within an RCU-sched read-side
> >>>> + * critical section.
> >>>> + *
> >>>> + * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
> >>>> + * and while lockdep is disabled.
> >>>> + *
> >>>> + * Note that if the CPU is in the idle loop from an RCU point of
> >>>> + * view (ie: that we are in the section between rcu_idle_enter() and
> >>>> + * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
> >>>> + * did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
> >>>> + * that are in such a section, considering these as in extended quiescent
> >>>> + * state, so such a CPU is effectively never in an RCU read-side critical
> >>>> + * section regardless of what RCU primitives it invokes. This state of
> >>>> + * affairs is required --- we need to keep an RCU-free window in idle
> >>>> + * where the CPU may possibly enter into low power mode. This way we can
> >>>> + * notice an extended quiescent state to other CPUs that started a grace
> >>>> + * period. Otherwise we would delay any grace period as long as we run in
> >>>> + * the idle task.
> >>>> + *
> >>>> + * Similarly, we avoid claiming an SRCU read lock held if the current
> >>>> + * CPU is offline.
> >>>> + */
> >>>> +#ifdef CONFIG_PREEMPT_COUNT
> >>>> +int rcu_read_lock_sched_held(void)
> >>>> +{
> >>>> + int lockdep_opinion = 0;
> >>>> +
> >>>> + if (!debug_lockdep_rcu_enabled())
> >>>> + return 1;
> >>>> + if (!rcu_is_watching())
> >>>> + return 0;
> >>>> + if (!rcu_lockdep_current_cpu_online())
> >>>> + return 0;
> >>>> + if (debug_locks)
> >>>> + lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
> >>>> + return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
> >>>> +}
> >>>> +EXPORT_SYMBOL(rcu_read_lock_sched_held);
> >>>> +#else
> >>>> +/* !CONFIG_PREEMPT_COUNT - the function is inlined to always return 1 */
> >>>
> >>> Nuke the #else. It's not needed and this is a common enough practice to
> >>> have the static inline foo() { } when disabled that we do not need to
> >>> comment about it here.
> >>
> >> Sending patch v2 in a few minutes.
> >>
> >>>> +#endif
> >>>
> >>> Hmm, you added two #ifdef, and one #endif. How does this even compile??
> >>
> >> Er... it... doesn't.
> >>
> >> There was "#if defined CONFIG_DEBUG_LOCK_ALLOC && defined CONFIG_PREEMPT_COUNT"
> >> but then I split it into two #ifs to have a nice explanatory empty
> >> #else clause. And I did not test it after that edit
> >> ("what could possibly go wrong?"). Sorry.
> >>
> >> Patch v2 I'm sending _is_ tested.
> >
> > Boot/run as well as build?
>
> I did not even dare to try booting 128 megabyte allyesconfig monstrosity,
> before you asked.
>
> It took me 4 hours of rebuilds to figure out that CONFIG_CMDLINE_BOOL needs to be
> disabled for my qemu boot to succeed :) :)
Just make sure you retain the .config file to allow you to more easily
test future changes! ;-)
> So, yes, patched allyesconfig kernel seems to boot... it takes 250 seconds in qemu.
Steve, are you OK with Denys's most recent patch?
Thanx, Paul
On Tue, 26 May 2015 08:18:03 -0700
"Paul E. McKenney" <[email protected]> wrote:
> Steve, are you OK with Denys's most recent patch?
The only comment I believe I had on it was the use of parenthesis
around the CONFIG names for defined(), as that seems to be the common
method used in the kernel.
-- Steve
On 05/26/2015 05:37 PM, Steven Rostedt wrote:
> On Tue, 26 May 2015 08:18:03 -0700
> "Paul E. McKenney" <[email protected]> wrote:
>
>> Steve, are you OK with Denys's most recent patch?
>
> The only comment I believe I had on it was the use of parenthesis
> around the CONFIG names for defined(), as that seems to be the common
> method used in the kernel.
I'm sending patch v3 with this change
On Tue, May 26, 2015 at 11:37:14AM -0400, Steven Rostedt wrote:
> On Tue, 26 May 2015 08:18:03 -0700
> "Paul E. McKenney" <[email protected]> wrote:
>
> > Steve, are you OK with Denys's most recent patch?
>
> The only comment I believe I had on it was the use of parenthesis
> around the CONFIG names for defined(), as that seems to be the common
> method used in the kernel.
So it sounds the next step is for Denys to send an update with the
parentheses.
Thanx, Paul