linux-kernel - [Q] missing unused dentry in prune

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Message-ID: <453F58FB.4050407@sw.ru>
Date:	Wed, 25 Oct 2006 16:30:51 +0400
From:	Vasily Averin <vvs@...ru>
To:	Neil Brown <neilb@...e.de>, Jan Blunck <jblunck@...e.de>,
	Olaf Hering <olh@...e.de>, Balbir Singh <balbir@...ibm.com>,
	David Howells <dhowells@...hat.com>,
	Kirill Korotaev <dev@...nvz.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org, Andrew Morton <akpm@...l.org>
Subject: [Q] missing unused dentry in prune_dcache()?

Hello folks,

I would like to ask you clarify me one question in the the following patch:
http://linux.bkbits.net:8080/linux-2.6/gnupatch@...b144ecSF1rYskg3q-SeR2vf88zg
# ChangeSet
#   2006/06/22 15:05:57-07:00 neilb@...e.de
#   [PATCH] Fix dcache race during umount

#   If prune_dcache finds a dentry that it cannot free, it leaves it where it
#   is (at the tail of the list) and exits, on the assumption that some other
#   thread will be removing that dentry soon.

However as far as I see this comment is not correct: when we cannot take
s_umount rw_semaphore (for example because it was taken in do_remount) this
dentry is already extracted from dentry_unused list and we do not add it into
the list again. Therefore dentry will not be found by prune_dcache() and
shrink_dcache_sb() and will leave in memory very long time until the partition
will be unmounted.

Am I probably err?

The patch adds this dentry into tail of the dentry_unused list.

Signed-off-by:	Vasily Averin <vvs@...ru>

--- linux-2.6.19-rc3/fs/dcache.c.prdch	2006-10-25 16:09:19.000000000 +0400
+++ linux-2.6.19-rc3/fs/dcache.c	2006-10-25 16:08:20.000000000 +0400
@@ -477,6 +477,8 @@ static void prune_dcache(int count, stru
 			}
 			up_read(s_umount);
 		}
+ 		list_add_tail(&dentry->d_lru, &dentry_unused);
+		dentry_stat.nr_unused++;
 		spin_unlock(&dentry->d_lock);
 		/* Cannot remove the first dentry, and it isn't appropriate
 		 * to move it to the head of the list, so give up, and try
-
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