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Re: [PATCH] xfs: re-enable xfsaild idle mode and fix associated races

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH] xfs: re-enable xfsaild idle mode and fix associated races
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Mon, 04 Jun 2012 12:25:40 -0500
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1337875602-63025-1-git-send-email-bfoster@xxxxxxxxxx>
References: <1337875602-63025-1-git-send-email-bfoster@xxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:9.0) Gecko/20120122 Thunderbird/9.0
On 05/24/12 11:06, Brian Foster wrote:
xfsaild idle mode logic currently leads to a couple hangs:

1.) If xfsaild is rescheduled in during an incremental scan
     (i.e., tout != 0) and the target has been updated since
     the previous run, we can hit the new target and go into
     idle mode with a still populated ail.
2.) A wake up is only issued when the target is pushed forward.
     The wake up can race with xfsaild if it is currently in the
     process of entering idle mode, causing future wake up
     events to be lost.

Both hangs are reproducible by running xfstests 273 in a loop.
Modify xfsaild to enter idle mode only when the ail is empty
and the push target has not been moved forward since the last
push.

Signed-off-by: Brian Foster<bfoster@xxxxxxxxxx>
---

I wouldn't mind keeping an large (a few minutes) wake up value for the
empty AIL case to be paranoid.

Reviewed-by: Mark Tinguely <tinguely@xxxxxxx>

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