linux-kernel - Re: [pre 3.16-rc1] Oops at spin_trylock(&inode->i

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Message-ID: <20140611160133.GX18016@ZenIV.linux.org.uk>
Date:	Wed, 11 Jun 2014 17:01:33 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	paulmck@...ux.vnet.ibm.com, torvalds@...ux-foundation.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [pre 3.16-rc1] Oops at spin_trylock(&inode->i_lock)

On Wed, Jun 11, 2014 at 08:35:44PM +0900, Tetsuo Handa wrote:
> I also confirmed that the command line which triggers this oops is
> 
>   mount -n -o ro,remount sysfs /sys
> 
> in /etc/init.d/halt script in CentOS 6.5.
> Manually executing the command line from login shell triggers this oops.
> 
> I don't know why but commit 59a3d4c363 revealed a refcount bug
> in sysfs (or maybe in vfs)?

Try to check if this helps:

diff --git a/fs/dcache.c b/fs/dcache.c
index be2bea8..e99c6f5 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -532,10 +532,12 @@ static inline struct dentry *lock_parent(struct dentry *dentry)
 	struct dentry *parent = dentry->d_parent;
 	if (IS_ROOT(dentry))
 		return NULL;
+	if (unlikely((int)dentry->d_lockref.count < 0))
+		return NULL;
 	if (likely(spin_trylock(&parent->d_lock)))
 		return parent;
-	spin_unlock(&dentry->d_lock);
 	rcu_read_lock();
+	spin_unlock(&dentry->d_lock);
 again:
 	parent = ACCESS_ONCE(dentry->d_parent);
 	spin_lock(&parent->d_lock);
--
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