linux-kernel - Re: Lockdep splat in autofs with 2.6.39-rc2

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Date:	Thu, 21 Apr 2011 17:25:37 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Nick Bowler <nbowler@...iptictech.com>
Cc:	linux-kernel@...r.kernel.org, autofs@...ux.kernel.org,
	Ian Kent <raven@...maw.net>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: Lockdep splat in autofs with 2.6.39-rc2

On Thu, Apr 07, 2011 at 03:44:03PM -0400, Nick Bowler wrote:
> Just saw this on 2.6.39-rc2 after half a day or so of uptime.  I've
> never seen it before today so it may be a regression from 2.6.38.
> Nothing seems have failed as a result.  Please let me know if you
> need any more info.
>

Could you try this patch. I know it may be hard to reproduce, but the
issue is that we are recursing down the locks in a tree/list and we changed a
lock from being nested to being a parent. This patch tells lockdep about
what we did.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>


diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 450f529..1feb68e 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -124,6 +124,7 @@ start:
 	/* Negative dentry - try next */
 	if (!simple_positive(q)) {
 		spin_unlock(&p->d_lock);
+		lock_set_subclass(&q->d_lock.dep_map, 0, _RET_IP_);
 		p = q;
 		goto again;
 	}
@@ -186,6 +187,7 @@ again:
 	/* Negative dentry - try next */
 	if (!simple_positive(ret)) {
 		spin_unlock(&p->d_lock);
+		lock_set_subclass(&ret->d_lock.dep_map, 0, _RET_IP_);
 		p = ret;
 		goto again;
 	}
--
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