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perf_counter: fix counter inheritance race

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Context rotation should not occur when we are in the middle of
walking the counter list when inheriting counters ...

[ Impact: fix occasionally incorrect perf stat results ]

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Ingo Molnar 2009-05-17 11:24:08 +02:00
parent 33b2fb303f
commit c44d70a340
2 changed files with 10 additions and 1 deletions
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1
include/linux/perf_counter.h
View File

@ -508,6 +508,7 @@ struct perf_counter_context {
int nr_counters;
int nr_active;
int is_active;
int rr_allowed;
struct task_struct *task;
/*

10
kernel/perf_counter.c
View File

@ -1120,7 +1120,8 @@ void perf_counter_task_tick(struct task_struct *curr, int cpu)
__perf_counter_task_sched_out(ctx);
rotate_ctx(&cpuctx->ctx);
rotate_ctx(ctx);
if (ctx->rr_allowed)
rotate_ctx(ctx);
perf_counter_cpu_sched_in(cpuctx, cpu);
perf_counter_task_sched_in(curr, cpu);
@ -3108,6 +3109,7 @@ __perf_counter_init_context(struct perf_counter_context *ctx,
mutex_init(&ctx->mutex);
INIT_LIST_HEAD(&ctx->counter_list);
INIT_LIST_HEAD(&ctx->event_list);
ctx->rr_allowed = 1;
ctx->task = task;
}
@ -3348,6 +3350,9 @@ void perf_counter_init_task(struct task_struct *child)
*/
mutex_lock(&parent_ctx->mutex);
parent_ctx->rr_allowed = 0;
barrier(); /* irqs */
/*
* We dont have to disable NMIs - we are only looking at
* the list, not manipulating it:
@ -3361,6 +3366,9 @@ void perf_counter_init_task(struct task_struct *child)
break;
}
barrier(); /* irqs */
parent_ctx->rr_allowed = 1;
mutex_unlock(&parent_ctx->mutex);
}