From: Jan Blunck <jblunck@suse.de>
To: Neil Brown <neilb@suse.de>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>,
Olaf Hering <olh@suse.de>, Kirill Korotaev <dev@openvz.org>,
Al Viro <viro@ftp.linux.org.uk>
Subject: Re: [PATCH] Busy inodes after unmount, be more verbose in generic_shutdown_super
Date: Fri, 3 Mar 2006 12:42:31 +0100 [thread overview]
Message-ID: <20060303114230.GL31712@hasse.suse.de> (raw)
In-Reply-To: <17414.38749.886125.282255@cse.unsw.edu.au>
On Thu, Mar 02, Neil Brown wrote:
> The core problem is that:
> prune_one_dentry can hold a reference to a dentry without any
> lock being held, and without any other reference to the
> filesystem (if it is being called from shrink_dcache_memory).
> It holds this reference while calling iput on an inode. This can
> take an arbitrarily long time to complete, especially if NFS
> needs to wait for some RPCs to complete or timeout.
>
> shrink_dcache_parent skips over dentries which have a reference,
> such as the one held by prune_one_dentry.
>
> Thus umount can find that an inode is still in use (by it's dentry
> which was skipped) and will complain. Worse, when the nfs request
> on some inode finally completes, it might find the superblock
> doesn't exist any more and... oops.
>
> My proposed solution to the problem is never to expose the reference
> held by prune_one_dentry. i.e. keep the spin_lock held.
This morning I wondered, why I was using a list to drop the dentry's inodes
after the dput() has visited all parents.
It is not enough to fix prune_one_dentry() to hold the lock until the parent
is dereferenced since prune_one_dentry() calls __dput_locked(). And in
__dput_locked() we have the same problem again:
from __dput_locked():
list_del(&dentry->d_u.d_child);
dentry_stat.nr_dentry--; /* For d_free, below */
/*drops the locks, at that point nobody can reach this dentry*/
-> dentry_iput(dentry);
parent = dentry->d_parent;
d_free(dentry);
if (dentry == parent)
return;
dentry = parent;
+
+ if (atomic_read(&dentry->d_count) == 1)
+ might_sleep();
+ if (!atomic_dec_and_lock(&dentry->d_count, &dcache_lock))
+ return;
+
+ spin_lock(&dentry->d_lock);
goto repeat;
}
}
Between -> and the atomic_dec_and_lock() the reference count on the parent is
wrong and no lock is held. I fixed that by using d_lru to keep track of all
dentry's which inodes still have to be dereferenced. This should happen after
all parents have been dereferenced.
Regards,
Jan
--
Jan Blunck jblunck@suse.de
SuSE LINUX AG - A Novell company
Maxfeldstr. 5 +49-911-74053-608
D-90409 Nürnberg http://www.suse.de
next prev parent reply other threads:[~2006-03-03 11:42 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-02 6:57 [PATCH] Busy inodes after unmount, be more verbose in generic_shutdown_super Neil Brown
2006-03-02 10:48 ` Jan Blunck
2006-03-03 11:42 ` Jan Blunck [this message]
2006-03-06 6:09 ` Neil Brown
2006-03-06 7:32 ` Balbir Singh
2006-03-07 1:58 ` Neil Brown
2006-03-07 2:49 ` Balbir Singh
2006-03-07 6:22 ` Kirill Korotaev
2006-03-07 6:16 ` Kirill Korotaev
2006-03-07 7:03 ` Balbir Singh
2006-03-07 7:21 ` Kirill Korotaev
2006-03-07 11:05 ` Balbir Singh
2006-03-08 0:29 ` Neil Brown
2006-03-08 2:17 ` Balbir Singh
2006-03-08 2:39 ` Neil Brown
2006-03-08 3:05 ` Balbir Singh
2006-03-08 11:01 ` Jan Blunck
2006-03-06 11:56 ` Jan Blunck
2006-03-07 2:15 ` Neil Brown
2006-03-06 11:56 ` Kirill Korotaev
2006-03-07 2:01 ` Neil Brown
2006-03-07 6:20 ` Kirill Korotaev
2006-03-07 23:20 ` Neil Brown
2006-03-09 12:03 ` Kirill Korotaev
-- strict thread matches above, loose matches on Subject: below --
2006-01-16 22:34 Olaf Hering
2006-01-16 23:23 ` Kirill Korotaev
2006-01-16 23:29 ` Olaf Hering
2006-01-17 2:05 ` Andrew Morton
2006-01-17 7:03 ` Kirill Korotaev
2006-01-18 22:49 ` Jan Blunck
2006-01-18 23:10 ` Andrew Morton
2006-01-19 10:08 ` Kirill Korotaev
2006-01-19 9:52 ` Kirill Korotaev
2006-01-19 10:04 ` Jan Blunck
2006-01-19 10:26 ` Kirill Korotaev
2006-01-20 19:06 ` Jan Blunck
2006-01-23 8:14 ` Kirill Korotaev
2006-01-30 11:54 ` Jan Blunck
2006-01-30 14:05 ` Kirill Korotaev
2006-01-30 14:21 ` Jan Blunck
2006-01-30 14:34 ` Kirill Korotaev
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