[PATCH] perf/core: fix perf_proc_update_handler() bug

[PATCH] perf/core: fix perf_proc_update_handler() bug

[Stephane Eranian]

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 <eranian@google.com>
---
 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

Re: [PATCH] perf/core: fix perf_proc_update_handler() bug

[Stephane Eranian]

On Thu, Jan 10, 2019 at 5:17 PM Stephane Eranian <eranian@google.com> 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 <eranian@google.com>

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
>

Re: [PATCH] perf/core: fix perf_proc_update_handler() bug

[Andi Kleen]

On Thu, Jan 17, 2019 at 01:03:20PM -0800, Stephane Eranian wrote:
> On Thu, Jan 10, 2019 at 5:17 PM Stephane Eranian <eranian@google.com> 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 <eranian@google.com>
> 
> Ping.

Reviewed-by: Andi Kleen <ak@linux.intel.com>

-Andi

Re: [PATCH] perf/core: fix perf_proc_update_handler() bug

[Jiri Olsa]

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 <eranian@google.com>

Reviewed-by: Jiri Olsa <jolsa@kernel.org>

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
> 

Re: [PATCH] perf/core: fix perf_proc_update_handler() bug

[Arnaldo Carvalho de Melo]

Em Thu, Jan 17, 2019 at 01:03:20PM -0800, Stephane Eranian escreveu:
> On Thu, Jan 10, 2019 at 5:17 PM Stephane Eranian <eranian@google.com> 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 <eranian@google.com>
> 
> 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

[tip:perf/urgent] perf core: Fix perf_proc_update_handler() bug

[tip-bot for Stephane Eranian]

Commit-ID:  1a51c5da5acc6c188c917ba572eebac5f8793432
Gitweb:     https://git.kernel.org/tip/1a51c5da5acc6c188c917ba572eebac5f8793432
Author:     Stephane Eranian <eranian@google.com>
AuthorDate: Thu, 10 Jan 2019 17:17:16 -0800
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
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 <eranian@google.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1547169436-6266-1-git-send-email-eranian@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 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();