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Subject[tip:perfcounters/core] perf_counter: Fix cpuctx->task_ctx races
Commit-ID:  3f4dee227348daac32f36daad9a91059efd0723e
Gitweb: http://git.kernel.org/tip/3f4dee227348daac32f36daad9a91059efd0723e
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Fri, 29 May 2009 11:25:09 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 29 May 2009 14:28:36 +0200

perf_counter: Fix cpuctx->task_ctx races

Peter noticed that we are sometimes reading cpuctx->task_ctx with
interrupts enabled.

Noticed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/perf_counter.c | 28 ++++++++++++++++++++--------
1 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index db843f8..eb34604 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -234,15 +234,18 @@ static void __perf_counter_remove_from_context(void *info)
struct perf_counter_context *ctx = counter->ctx;
unsigned long flags;

+ local_irq_save(flags);
/*
* If this is a task context, we need to check whether it is
* the current task context of this cpu. If not it has been
* scheduled out before the smp call arrived.
*/
- if (ctx->task && cpuctx->task_ctx != ctx)
+ if (ctx->task && cpuctx->task_ctx != ctx) {
+ local_irq_restore(flags);
return;
+ }

- spin_lock_irqsave(&ctx->lock, flags);
+ spin_lock(&ctx->lock);
/*
* Protect the list operation against NMI by disabling the
* counters on a global level.
@@ -382,14 +385,17 @@ static void __perf_counter_disable(void *info)
struct perf_counter_context *ctx = counter->ctx;
unsigned long flags;

+ local_irq_save(flags);
/*
* If this is a per-task counter, need to check whether this
* counter's task is the current task on this cpu.
*/
- if (ctx->task && cpuctx->task_ctx != ctx)
+ if (ctx->task && cpuctx->task_ctx != ctx) {
+ local_irq_restore(flags);
return;
+ }

- spin_lock_irqsave(&ctx->lock, flags);
+ spin_lock(&ctx->lock);

/*
* If the counter is on, turn it off.
@@ -615,6 +621,7 @@ static void __perf_install_in_context(void *info)
unsigned long flags;
int err;

+ local_irq_save(flags);
/*
* If this is a task context, we need to check whether it is
* the current task context of this cpu. If not it has been
@@ -623,12 +630,14 @@ static void __perf_install_in_context(void *info)
* on this cpu because it had no counters.
*/
if (ctx->task && cpuctx->task_ctx != ctx) {
- if (cpuctx->task_ctx || ctx->task != current)
+ if (cpuctx->task_ctx || ctx->task != current) {
+ local_irq_restore(flags);
return;
+ }
cpuctx->task_ctx = ctx;
}

- spin_lock_irqsave(&ctx->lock, flags);
+ spin_lock(&ctx->lock);
ctx->is_active = 1;
update_context_time(ctx);

@@ -745,17 +754,20 @@ static void __perf_counter_enable(void *info)
unsigned long flags;
int err;

+ local_irq_save(flags);
/*
* If this is a per-task counter, need to check whether this
* counter's task is the current task on this cpu.
*/
if (ctx->task && cpuctx->task_ctx != ctx) {
- if (cpuctx->task_ctx || ctx->task != current)
+ if (cpuctx->task_ctx || ctx->task != current) {
+ local_irq_restore(flags);
return;
+ }
cpuctx->task_ctx = ctx;
}

- spin_lock_irqsave(&ctx->lock, flags);
+ spin_lock(&ctx->lock);
ctx->is_active = 1;
update_context_time(ctx);


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