4.20-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 1a51c5da5acc6c188c917ba572eebac5f8793432 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 699bc25d6204..18997730b665 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();