Re: [PATCH 04/21] sched: Change the ttwu success details

From: Peter Zijlstra
Date: Wed Apr 13 2011 - 06:46:27 EST

On Wed, 2011-04-13 at 11:23 +0200, Peter Zijlstra wrote:
> and workqueue wakeups, and I doubt extra wakeups will cause lockups.

Damn assumptions ;-)

Index: linux-2.6/kernel/sched.c
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2447,7 +2447,7 @@ static inline void ttwu_post_activation(
/* if a worker is waking up, notify workqueue */
- if ((p->flags & PF_WQ_WORKER) && success)
+ if (p->flags & PF_WQ_WORKER)
wq_worker_waking_up(p, cpu_of(rq));

Appears to be sufficient to cause the lockup, so somehow the whole
workqueue stuff relies on the fact that waking a TASK_(UN)INTERRUPTIBLE
task that hasn't been dequeued yet isn't a wakeup.

Tejun any quick clues as to why and how to cure this?

/me goes read that stuff

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