[PATCH] perf: Prevent divide by zero exception in kernel/events/core.c

[Knut Petersen <Knut_Petersen@t-online.de>]

[-- Attachment #1: Type: text/plain, Size: 293 bytes --]

Any value written to /proc/sys/kernel/perf_event_max_sample_rate
is accepted and used as a divisor in perf_proc_update_handler().

Obviously that is wrong. 0 will cause a divide by 0 exception,
and negative values are unreasonable.

The attached patch enforces a lower limit of 1.

cu,
  Knut

[-- Attachment #2: 0001-Enforce-1-as-lower-limit-for-perf_event_max_sample_r.patch --]
[-- Type: text/x-patch, Size: 1122 bytes --]

>From 7f468bd7bad2f2fec2e93c89a48008d1cba99001 Mon Sep 17 00:00:00 2001
From: Knut Petersen <Knut_Petersen@t-online.de>
Date: Wed, 25 Sep 2013 13:34:57 +0200
Subject: [PATCH] Enforce 1 as lower limit for perf_event_max_sample_rate

/proc/sys/kernel/perf_event_max_sample_rate will accept
negative values as well as 0.

Negative values are unreasonable, and 0 causes a
divide by zero exception in perf_proc_update_handler.

This patch enforces a lower limit of 1.

Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>
---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index dd236b6..350bb53 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -198,6 +198,9 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
 	if (ret || !write)
 		return ret;
 
+	if (sysctl_perf_event_sample_rate <= 0)
+		sysctl_perf_event_sample_rate = 1;
+
 	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();
-- 
1.8.1.4