x86, bts: wait until traced task has been scheduled out (8d99b3ac) · Commits · 戴 / test

In order to stop branch tracing for a running task, we need to first clear the branch tracing control bits before we may free the tracing buffer. If the traced task is running, the cpu might still trace that task after the branch trace control bits have cleared. Wait until the traced task has been scheduled out before proceeding. A similar problem affects the task debug store context. We first remove the context, then we need to wait until the task has been scheduled out before we can free the context memory. Reviewed-by:

Oleg Nesterov <oleg@redhat.com> Signed-off-by:

Markus Metzger <markus.t.metzger@intel.com> Cc: roland@redhat.com Cc: eranian@googlemail.com Cc: juan.villacis@intel.com Cc: ak@linux.jf.intel.com LKML-Reference: <20090403144551.919636000@intel.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/ds.c

+19 −4

Original line number	Diff line number	Diff line
		@@ -299,6 +299,7 @@ static inline struct ds_context ds_get_context(struct task_struct task)

		static inline void ds_put_context(struct ds_context *context)
		{
		struct task_struct *task;
		unsigned long irq;

		if (!context)
		@@ -313,14 +314,20 @@ static inline void ds_put_context(struct ds_context *context)

		*(context->this) = NULL;

		if (context->task)
		clear_tsk_thread_flag(context->task, TIF_DS_AREA_MSR);
		task = context->task;

		if (task)
		clear_tsk_thread_flag(task, TIF_DS_AREA_MSR);

		if (!context->task \|\| (context->task == current))
		if (!task \|\| (task == current))
		wrmsrl(MSR_IA32_DS_AREA, 0);

		spin_unlock_irqrestore(&ds_lock, irq);

		/* The context might still be in use for context switching. */
		if (task && (task != current))
		wait_task_context_switch(task);

		kfree(context);
		}

		@@ -781,15 +788,23 @@ struct pebs_tracer ds_request_pebs(struct task_struct task,

		void ds_release_bts(struct bts_tracer *tracer)
		{
		struct task_struct *task;

		if (!tracer)
		return;

		task = tracer->ds.context->task;

		ds_suspend_bts(tracer);

		WARN_ON_ONCE(tracer->ds.context->bts_master != tracer);
		tracer->ds.context->bts_master = NULL;

		put_tracer(tracer->ds.context->task);
		/* Make sure tracing stopped and the tracer is not in use. */
		if (task && (task != current))
		wait_task_context_switch(task);

		put_tracer(task);
		ds_put_context(tracer->ds.context);

		kfree(tracer);

Admin message