Commit b58f6b0d authored Jun 07, 2011 by Peter Zijlstra Committed by Ingo Molnar Jun 07, 2011

perf, core: Fix initial task_ctx/event installation



A lost Quilt refresh of 2c29ef0f (perf: Simplify and fix
__perf_install_in_context()) is causing grief and lockups,
reported by Jiri Olsa.

When installing an event in a task context, there's a number of
issues:

 - there might not be an existing task context, in which case
   we should install the now current context;

 - there might already be a context, not the current one, in
   which case we should de-schedule the old and install the new;

these cases were dealt with in the lost refresh, however there is one
further case that was found in testing:

 - there might already be a context, the current one, in which
   case we should still de-schedule, and should take care
   to re-install it (note that task_ctx_sched_out() clears
   cpuctx->task_ctx).

Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1307399008.2497.971.camel@laptop


Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 3ce2a0bc

kernel/events/core.c

+17 −11

Original line number	Diff line number	Diff line
		@@ -1505,25 +1505,31 @@ static int __perf_install_in_context(void *info)
		struct perf_event_context *task_ctx = cpuctx->task_ctx;
		struct task_struct *task = current;

		perf_ctx_lock(cpuctx, cpuctx->task_ctx);
		perf_ctx_lock(cpuctx, task_ctx);
		perf_pmu_disable(cpuctx->ctx.pmu);

		/*
		* If there was an active task_ctx schedule it out.
		*/
		if (task_ctx) {
		if (task_ctx)
		task_ctx_sched_out(task_ctx);

		/*
		* If the context we're installing events in is not the
		* active task_ctx, flip them.
		*/
		if (ctx->task && task_ctx != ctx) {
		raw_spin_unlock(&cpuctx->ctx.lock);
		if (task_ctx)
		raw_spin_unlock(&task_ctx->lock);
		raw_spin_lock(&ctx->lock);
		cpuctx->task_ctx = task_ctx = ctx;
		task_ctx = ctx;
		}

		if (task_ctx) {
		cpuctx->task_ctx = task_ctx;
		task = task_ctx->task;
		}

		cpu_ctx_sched_out(cpuctx, EVENT_ALL);

		update_context_time(ctx);

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