linux-kernel - Re: [vfsmounts] WARNING: CPU: 1 PID: 479 at fs/dcache.c:385 d_lru

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Date:	Sat, 9 Nov 2013 05:19:31 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [vfsmounts] WARNING: CPU: 1 PID: 479 at fs/dcache.c:385
 d_lru_del()

On Sat, Nov 09, 2013 at 11:06:36AM +0800, Fengguang Wu wrote:
> Greetings,
> 
> I got the below dmesg and the first bad commit is
> 
> commit 84550b9356af50c7cbd6b6ce6e8fd06585eebf14
> Author: Al Viro <viro@...iv.linux.org.uk>
> Date:   Sun Sep 29 22:06:07 2013 -0400

	Got it...  See if the following fixes the problem - it's
shrink_dcache_for_umount() needing to be careful after possible
run of d_genocide(); we are left with dentries that have zero
refcount and are not on any LRU.  And yes, it's d_genocide() being
not nice, exactly because it relies upon shrink_dcache_for_umount()
coming right after it to sweep the garbage.  So we'd better be
ready to deal with said garbage...

	Diff below fixes that junk here.  Folded and re-pushed...

diff --git a/fs/dcache.c b/fs/dcache.c
index 50d4357..72c99b8 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1391,7 +1391,8 @@ static enum d_walk_ret umount_collect(void *_data, struct dentry *dentry)
 		 * need to get the global LRU lock and do the
 		 * LRU accounting.
 		 */
-		d_lru_del(dentry);
+		if (dentry->d_flags & DCACHE_LRU_LIST)
+			d_lru_del(dentry);
 		d_shrink_add(dentry, &data->dispose);
 		data->found++;
 		ret = D_WALK_NORETRY;
--
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