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

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

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On 25.09.2013 14:12, Peter Zijlstra wrote:
> The 'normal' way of doing that is changing the sysctl table entry to use
> proc_dointvec_minmax and set .extra = &one. See for example
> &sysctl_sched_cfs_bandwidth_slice in kernel/sysctl.c

Thanks. V2 attached.

cu,
  Knut

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>From 4ef9dabdd27a02e2ebd45c2d98afda7e43e82ab3 Mon Sep 17 00:00:00 2001
From: Knut Petersen <Knut_Petersen@t-online.de>
Date: Wed, 25 Sep 2013 14:29:37 +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.

v2: Use proc_dointvec_minmax() as suggested by
Peter Zijlstra.

Signed-off-by: Knut Petersen <Knut_Petersen@t-online.de>
---
 kernel/events/core.c | 2 +-
 kernel/sysctl.c      | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index dd236b6..8721a17 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -193,7 +193,7 @@ int perf_proc_update_handler(struct ctl_table *table, int write,
 		void __user *buffer, size_t *lenp,
 		loff_t *ppos)
 {
-	int ret = proc_dointvec(table, write, buffer, lenp, ppos);
+	int ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 
 	if (ret || !write)
 		return ret;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b2f06f3..2a9db91 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1049,6 +1049,7 @@ static struct ctl_table kern_table[] = {
 		.maxlen		= sizeof(sysctl_perf_event_sample_rate),
 		.mode		= 0644,
 		.proc_handler	= perf_proc_update_handler,
+		.extra1		= &one,
 	},
 	{
 		.procname	= "perf_cpu_time_max_percent",
-- 
1.8.1.4