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Date: Wed, 23 May 2012 13:48:54 -0400
From: Brian Foster <bfoster@redhat.com>
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Subject: Re: [RFC PATCH v3 2/2] xfs: fix xfsaild hang due to lost wake ups
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To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com

On 05/22/2012 08:58 PM, Dave Chinner wrote:
snip
> 
> Finally, rather than calling wake_up_process() in the
> xfs_ail_push*() functions, call wake_up(&ailp->xa_idle); There can
> only be one thread sleeping on that (the xfsaild) so there is no
> need to use the wake_up_all() variant...
> 
> FWIW, you might be able to do this without the idle wait queue and
> just use wake_up_process() - 
> 

Hi Dave,

I have a working version of your suggested algorithm. It looks mostly the same with the exception of a spin_unlock fix. I also have the below version that uses a wait_queue and that I plan to test overnight tonight:

	while (!kthread_should_stop()) {
		if (tout && tout <= 20)
			state = TASK_KILLABLE;
		else
			state = TASK_INTERRUPTIBLE;

		prepare_to_wait(&ailp->xa_idle, &wait, state);

		spin_lock(&ailp->xa_lock);
		/* barrier matches the xa_target update in xfs_ail_push() */
		smp_rmb();
		if (!xfs_ail_min(ailp) && (ailp->xa_target == ailp->xa_target_prev)) {
			/* the ail is empty and no change to the push target - idle */
			spin_unlock(&ailp->xa_lock);
			schedule();
		} else if (tout) {
			spin_unlock(&ailp->xa_lock);
			/* more work to do soon */
			schedule_timeout(msecs_to_jiffies(tout));
		} else {
			spin_unlock(&ailp->xa_lock);
		}

		finish_wait(&ailp->xa_idle, &wait);

		try_to_freeze();

		tout = xfsaild_push(ailp);
	}

... and obviously the xfs_ail_push() side changes to:

	wake_up(&ailp->xa_idle);

Does this wait_queue version look sane to you? Thanks again..

Brian

> Cheers,
> 
> Dave.

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