The perf_proc_update_handler() handles /proc/sys/kernel/perf_event_max_sample_rate
syctl variable. When the PMU IRQ handler timing monitoring is disabled, i.e,
when /proc/sys/kernel/perf_cpu_time_max_percent is equal to 0 or 100,
then no modification to sysctl_perf_event_sample_rate is allowed to prevent
possible hang from wrong values.
The problem is that the test to prevent modification is made after the
sysctl variable is modified in perf_proc_update_handler().
You get an error:
$ echo 10001 >/proc/sys/kernel/perf_event_max_sample_rate
echo: write error: invalid argument
But the value is still modified causing all sorts of inconsistencies:
$ cat /proc/sys/kernel/perf_event_max_sample_rate
10001
This patch fixes the problem by moving the parsing of the value after
the test.
Signed-off-by: Stephane Eranian <[email protected]>
---
kernel/events/core.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 3cd13a30f732..e5ede6918050 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -436,18 +436,18 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
{
- int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
-
- if (ret || !write)
- return ret;
-
+ int ret;
+ int perf_cpu = sysctl_perf_cpu_time_max_percent;
/*
* If throttling is disabled don't allow the write:
*/
- if (sysctl_perf_cpu_time_max_percent == 100 ||
- sysctl_perf_cpu_time_max_percent == 0)
+ if (write && (perf_cpu == 100 || perf_cpu == 0))
return -EINVAL;
+ ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ if (ret || !write)
+ return ret;
+
max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
update_perf_cpu_limits();
--
2.7.4
On Thu, Jan 10, 2019 at 5:17 PM Stephane Eranian <[email protected]> wrote:
>
> The perf_proc_update_handler() handles /proc/sys/kernel/perf_event_max_sample_rate
> syctl variable. When the PMU IRQ handler timing monitoring is disabled, i.e,
> when /proc/sys/kernel/perf_cpu_time_max_percent is equal to 0 or 100,
> then no modification to sysctl_perf_event_sample_rate is allowed to prevent
> possible hang from wrong values.
>
> The problem is that the test to prevent modification is made after the
> sysctl variable is modified in perf_proc_update_handler().
>
> You get an error:
>
> $ echo 10001 >/proc/sys/kernel/perf_event_max_sample_rate
> echo: write error: invalid argument
>
> But the value is still modified causing all sorts of inconsistencies:
>
> $ cat /proc/sys/kernel/perf_event_max_sample_rate
> 10001
>
> This patch fixes the problem by moving the parsing of the value after
> the test.
>
> Signed-off-by: Stephane Eranian <[email protected]>
Ping.
> ---
> kernel/events/core.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 3cd13a30f732..e5ede6918050 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -436,18 +436,18 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
> void __user *buffer, size_t *lenp,
> loff_t *ppos)
> {
> - int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> -
> - if (ret || !write)
> - return ret;
> -
> + int ret;
> + int perf_cpu = sysctl_perf_cpu_time_max_percent;
> /*
> * If throttling is disabled don't allow the write:
> */
> - if (sysctl_perf_cpu_time_max_percent == 100 ||
> - sysctl_perf_cpu_time_max_percent == 0)
> + if (write && (perf_cpu == 100 || perf_cpu == 0))
> return -EINVAL;
>
> + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> + if (ret || !write)
> + return ret;
> +
> max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
> perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
> update_perf_cpu_limits();
> --
> 2.7.4
>
On Thu, Jan 17, 2019 at 01:03:20PM -0800, Stephane Eranian wrote:
> On Thu, Jan 10, 2019 at 5:17 PM Stephane Eranian <[email protected]> wrote:
> >
> > The perf_proc_update_handler() handles /proc/sys/kernel/perf_event_max_sample_rate
> > syctl variable. When the PMU IRQ handler timing monitoring is disabled, i.e,
> > when /proc/sys/kernel/perf_cpu_time_max_percent is equal to 0 or 100,
> > then no modification to sysctl_perf_event_sample_rate is allowed to prevent
> > possible hang from wrong values.
> >
> > The problem is that the test to prevent modification is made after the
> > sysctl variable is modified in perf_proc_update_handler().
> >
> > You get an error:
> >
> > $ echo 10001 >/proc/sys/kernel/perf_event_max_sample_rate
> > echo: write error: invalid argument
> >
> > But the value is still modified causing all sorts of inconsistencies:
> >
> > $ cat /proc/sys/kernel/perf_event_max_sample_rate
> > 10001
> >
> > This patch fixes the problem by moving the parsing of the value after
> > the test.
> >
> > Signed-off-by: Stephane Eranian <[email protected]>
>
> Ping.
Reviewed-by: Andi Kleen <[email protected]>
-Andi
On Thu, Jan 10, 2019 at 05:17:16PM -0800, Stephane Eranian wrote:
> The perf_proc_update_handler() handles /proc/sys/kernel/perf_event_max_sample_rate
> syctl variable. When the PMU IRQ handler timing monitoring is disabled, i.e,
> when /proc/sys/kernel/perf_cpu_time_max_percent is equal to 0 or 100,
> then no modification to sysctl_perf_event_sample_rate is allowed to prevent
> possible hang from wrong values.
>
> The problem is that the test to prevent modification is made after the
> sysctl variable is modified in perf_proc_update_handler().
>
> You get an error:
>
> $ echo 10001 >/proc/sys/kernel/perf_event_max_sample_rate
> echo: write error: invalid argument
>
> But the value is still modified causing all sorts of inconsistencies:
>
> $ cat /proc/sys/kernel/perf_event_max_sample_rate
> 10001
>
> This patch fixes the problem by moving the parsing of the value after
> the test.
>
> Signed-off-by: Stephane Eranian <[email protected]>
Reviewed-by: Jiri Olsa <[email protected]>
jirka
> ---
> kernel/events/core.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 3cd13a30f732..e5ede6918050 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -436,18 +436,18 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
> void __user *buffer, size_t *lenp,
> loff_t *ppos)
> {
> - int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> -
> - if (ret || !write)
> - return ret;
> -
> + int ret;
> + int perf_cpu = sysctl_perf_cpu_time_max_percent;
> /*
> * If throttling is disabled don't allow the write:
> */
> - if (sysctl_perf_cpu_time_max_percent == 100 ||
> - sysctl_perf_cpu_time_max_percent == 0)
> + if (write && (perf_cpu == 100 || perf_cpu == 0))
> return -EINVAL;
>
> + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> + if (ret || !write)
> + return ret;
> +
> max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
> perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
> update_perf_cpu_limits();
> --
> 2.7.4
>
Em Thu, Jan 17, 2019 at 01:03:20PM -0800, Stephane Eranian escreveu:
> On Thu, Jan 10, 2019 at 5:17 PM Stephane Eranian <[email protected]> wrote:
> >
> > The perf_proc_update_handler() handles /proc/sys/kernel/perf_event_max_sample_rate
> > syctl variable. When the PMU IRQ handler timing monitoring is disabled, i.e,
> > when /proc/sys/kernel/perf_cpu_time_max_percent is equal to 0 or 100,
> > then no modification to sysctl_perf_event_sample_rate is allowed to prevent
> > possible hang from wrong values.
> >
> > The problem is that the test to prevent modification is made after the
> > sysctl variable is modified in perf_proc_update_handler().
> >
> > You get an error:
> >
> > $ echo 10001 >/proc/sys/kernel/perf_event_max_sample_rate
> > echo: write error: invalid argument
> >
> > But the value is still modified causing all sorts of inconsistencies:
> >
> > $ cat /proc/sys/kernel/perf_event_max_sample_rate
> > 10001
> >
> > This patch fixes the problem by moving the parsing of the value after
> > the test.
> >
> > Signed-off-by: Stephane Eranian <[email protected]>
>
> Ping.
Collected the Reviewed-by from Jiri and Andi, reproduced the problem
before the patch and I'm testing it to push to Ingo via perf/urgent,
thanks for the patch.
- Arnaldo
Commit-ID: 1a51c5da5acc6c188c917ba572eebac5f8793432
Gitweb: https://git.kernel.org/tip/1a51c5da5acc6c188c917ba572eebac5f8793432
Author: Stephane Eranian <[email protected]>
AuthorDate: Thu, 10 Jan 2019 17:17:16 -0800
Committer: Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Fri, 18 Jan 2019 11:10:38 -0300
perf core: Fix perf_proc_update_handler() bug
The perf_proc_update_handler() handles /proc/sys/kernel/perf_event_max_sample_rate
syctl variable. When the PMU IRQ handler timing monitoring is disabled, i.e,
when /proc/sys/kernel/perf_cpu_time_max_percent is equal to 0 or 100,
then no modification to sysctl_perf_event_sample_rate is allowed to prevent
possible hang from wrong values.
The problem is that the test to prevent modification is made after the
sysctl variable is modified in perf_proc_update_handler().
You get an error:
$ echo 10001 >/proc/sys/kernel/perf_event_max_sample_rate
echo: write error: invalid argument
But the value is still modified causing all sorts of inconsistencies:
$ cat /proc/sys/kernel/perf_event_max_sample_rate
10001
This patch fixes the problem by moving the parsing of the value after
the test.
Committer testing:
# echo 100 > /proc/sys/kernel/perf_cpu_time_max_percent
# echo 10001 > /proc/sys/kernel/perf_event_max_sample_rate
-bash: echo: write error: Invalid argument
# cat /proc/sys/kernel/perf_event_max_sample_rate
10001
#
Signed-off-by: Stephane Eranian <[email protected]>
Reviewed-by: Andi Kleen <[email protected]>
Reviewed-by: Jiri Olsa <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
---
kernel/events/core.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 3cd13a30f732..e5ede6918050 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -436,18 +436,18 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp,
loff_t *ppos)
{
- int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
-
- if (ret || !write)
- return ret;
-
+ int ret;
+ int perf_cpu = sysctl_perf_cpu_time_max_percent;
/*
* If throttling is disabled don't allow the write:
*/
- if (sysctl_perf_cpu_time_max_percent == 100 ||
- sysctl_perf_cpu_time_max_percent == 0)
+ if (write && (perf_cpu == 100 || perf_cpu == 0))
return -EINVAL;
+ ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ if (ret || !write)
+ return ret;
+
max_samples_per_tick = DIV_ROUND_UP(sysctl_perf_event_sample_rate, HZ);
perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
update_perf_cpu_limits();