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Commit 3f4dee22 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

perf_counter: Fix cpuctx->task_ctx races 



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

Noticed-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent ad3a37de

kernel/perf_counter.c

+20 −8
Original line number Diff line number Diff line
@@ -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);