* [PATCH] perf: Prevent divide by zero exception in kernel/events/core.c @ 2013-09-25 12:07 Knut Petersen 2013-09-25 12:12 ` Peter Zijlstra 0 siblings, 1 reply; 4+ messages in thread From: Knut Petersen @ 2013-09-25 12:07 UTC (permalink / raw) To: Linus Torvalds Cc: Peter Zijlstra, Paul Mackerras, Ingo Molnar, Arnaldo Carvalho de Melo, linux-kernel [-- 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 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] perf: Prevent divide by zero exception in kernel/events/core.c 2013-09-25 12:07 [PATCH] perf: Prevent divide by zero exception in kernel/events/core.c Knut Petersen @ 2013-09-25 12:12 ` Peter Zijlstra 2013-09-25 12:46 ` Knut Petersen 0 siblings, 1 reply; 4+ messages in thread From: Peter Zijlstra @ 2013-09-25 12:12 UTC (permalink / raw) To: Knut Petersen Cc: Linus Torvalds, Paul Mackerras, Ingo Molnar, Arnaldo Carvalho de Melo, linux-kernel On Wed, Sep 25, 2013 at 02:07:35PM +0200, Knut Petersen wrote: > 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(); 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] perf: Prevent divide by zero exception in kernel/events/core.c 2013-09-25 12:12 ` Peter Zijlstra @ 2013-09-25 12:46 ` Knut Petersen 2013-10-04 17:32 ` [tip:perf/core] perf: Enforce 1 as lower limit for perf_event_max_sample_rate tip-bot for Knut Petersen 0 siblings, 1 reply; 4+ messages in thread From: Knut Petersen @ 2013-09-25 12:46 UTC (permalink / raw) To: Peter Zijlstra Cc: Linus Torvalds, Paul Mackerras, Ingo Molnar, Arnaldo Carvalho de Melo, linux-kernel [-- Attachment #1: Type: text/plain, Size: 269 bytes --] 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 [-- Attachment #2: 0001-Enforce-1-as-lower-limit-for-perf_event_max_sample_r.patch --] [-- Type: text/x-patch, Size: 1533 bytes --] >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 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* [tip:perf/core] perf: Enforce 1 as lower limit for perf_event_max_sample_rate 2013-09-25 12:46 ` Knut Petersen @ 2013-10-04 17:32 ` tip-bot for Knut Petersen 0 siblings, 0 replies; 4+ messages in thread From: tip-bot for Knut Petersen @ 2013-10-04 17:32 UTC (permalink / raw) To: linux-tip-commits; +Cc: linux-kernel, hpa, mingo, peterz, Knut_Petersen, tglx Commit-ID: 723478c8a471403c53cf144999701f6e0c4bbd11 Gitweb: http://git.kernel.org/tip/723478c8a471403c53cf144999701f6e0c4bbd11 Author: Knut Petersen <Knut_Petersen@t-online.de> AuthorDate: Wed, 25 Sep 2013 14:29:37 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Fri, 4 Oct 2013 10:06:07 +0200 perf: 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> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/5242DB0C.4070005@t-online.de Signed-off-by: Ingo Molnar <mingo@kernel.org> --- 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 d49a9d2..b25d65c 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", ^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2013-10-04 17:32 UTC | newest] Thread overview: 4+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2013-09-25 12:07 [PATCH] perf: Prevent divide by zero exception in kernel/events/core.c Knut Petersen 2013-09-25 12:12 ` Peter Zijlstra 2013-09-25 12:46 ` Knut Petersen 2013-10-04 17:32 ` [tip:perf/core] perf: Enforce 1 as lower limit for perf_event_max_sample_rate tip-bot for Knut Petersen
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