Re: [BUG] perf: hard lockup when using perf-sched

[Mike Galbraith]

On Thu, 2010-03-25 at 10:27 +0100, Mike Galbraith wrote:
> On Thu, 2010-03-25 at 16:04 +0800, Li Zefan wrote:
> > Mike Galbraith wrote:
> > > On Wed, 2010-03-24 at 08:32 +0100, Mike Galbraith wrote:
> > > 
> > >> I just saw this, hunted down your testcase and tried it here.  Looks
> > >> like perf_output_lock() wedged box.
> > > 
> > > (turns on frame pointers, and adds noinline)
> > > 
> > 
> > Thanks! Then who's going to fix this...
> 
> Well, that kinda depends on whether I figure out how the heck it's all
> supposed to work before somebody else whacks it or not.

This seems to work, in contrast to everything I tried yesterday.  Not
exactly a thing of beauty, but at least it's an option, so...

perf: fix perf sched record forkbomb deadlock

perf sched record can deadlock a box should the holder of handle->data->lock
take an interrupt, and then attempt to acquire an rq lock held by a CPU trying
to acquire the same lock.  Disable interrupts.

Signed-off-by: Mike Galbraith <efault@xxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Reported-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
LKML-Reference: <new-submission>

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 574ee58..2ba2e9f 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3378,15 +3378,23 @@ static void perf_event_task_output(struct perf_event *event,
 				     struct perf_task_event *task_event)
 {
 	struct perf_output_handle handle;
-	int size;
 	struct task_struct *task = task_event->task;
-	int ret;
+	unsigned long flags;
+	int size, ret;
+
+	/*
+	 * If this CPU attempts to acquire an rq lock held by a CPU spinning
+	 * in perf_output_lock() from interrupt context, it's game over.
+	 */
+	local_irq_save(flags);
 
 	size  = task_event->event_id.header.size;
 	ret = perf_output_begin(&handle, event, size, 0, 0);
 
-	if (ret)
+	if (ret) {
+		local_irq_restore(flags);
 		return;
+	}
 
 	task_event->event_id.pid = perf_event_pid(event, task);
 	task_event->event_id.ppid = perf_event_pid(event, current);
@@ -3397,6 +3405,7 @@ static void perf_event_task_output(struct perf_event *event,
 	perf_output_put(&handle, task_event->event_id);
 
 	perf_output_end(&handle);
+	local_irq_restore(flags);
 }
 
 static int perf_event_task_match(struct perf_event *event)


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