Re: [patch 1/4] jffs2: unlock f->sem on error in jffs2_new_inode()

[Brian Norris <computersforpeace@gmail.com>]

+ linux-mtd

Hi Wang,

On Thu, Feb 27, 2014 at 08:53:37AM +0800, Wang Nan wrote:
> On 2014/2/26 10:03, Brian Norris wrote:
> > On Wed, Feb 12, 2014 at 12:44:54PM -0800, Andrew Morton wrote:
> >> From: Wang Guoli <andy.wangguoli@huawei.com>
> >> Subject: jffs2: unlock f->sem on error in jffs2_new_inode()
> >>
> >> If jffs2_new_inode() succeeds, it returns with f->sem held, and the caller
> >> is responsible for releasing the lock.  If it fails, it still returns with
> >> the lock held, but the caller won't release the lock, which will lead to
> >> deadlock.
> > 
> > Have you actually seen a deadlock for this? AFAICT, the error cases for
> > jffs2_new_inode() all occur before anyone else actually has a reference
> > to the inode, so I don't expect that we should see the deadlock.
> > 
> 
> We found this bug by reading code. There's no deadlock have been actually seen.

Hmm, then I think maybe we should drop the stable tag. I'm not sure it's
a practical issue, and it also has unrelated indentation changes. That
means it breaks two of the rules in
Documentation/stable_kernel_rules.txt. I'm dropping the stable tag
unless someone shouts.

> >> Fix it by releasing the lock in jffs2_new_inode() on error.
> >>
> >> Signed-off-by: Wang Guoli <andy.wangguoli@huawei.com>
> >> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> >> Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
> >> Cc: David Woodhouse <dwmw2@infradead.org>
> >> Cc: Wang Guoli <andy.wangguoli@huawei.com>
> >> Cc: Brian Norris <computersforpeace@gmail.com>
> >> Cc: <stable@vger.kernel.org> # 2.6.34+
> >> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> >> ---
> >>
> >>  fs/jffs2/fs.c |    9 ++++++---
> >>  1 file changed, 6 insertions(+), 3 deletions(-)
> >>
> >> diff -puN fs/jffs2/fs.c~jffs2-unlock-f-sem-on-error-in-jffs2_new_inode fs/jffs2/fs.c
> >> --- a/fs/jffs2/fs.c~jffs2-unlock-f-sem-on-error-in-jffs2_new_inode
> >> +++ a/fs/jffs2/fs.c
> >> @@ -457,12 +457,14 @@ struct inode *jffs2_new_inode (struct in
> >>  	   The umask is only applied if there's no default ACL */
> >>  	ret = jffs2_init_acl_pre(dir_i, inode, &mode);
> >>  	if (ret) {
> >> -	    make_bad_inode(inode);
> >> -	    iput(inode);
> >> -	    return ERR_PTR(ret);
> >> +		mutex_unlock(&f->sem);
> >> +		make_bad_inode(inode);
> >> +		iput(inode);
> >> +		return ERR_PTR(ret);
> >>  	}
> >>  	ret = jffs2_do_new_inode (c, f, mode, ri);
> >>  	if (ret) {
> >> +		mutex_unlock(&f->sem);
> >>  		make_bad_inode(inode);
> >>  		iput(inode);
> >>  		return ERR_PTR(ret);
> >> @@ -479,6 +481,7 @@ struct inode *jffs2_new_inode (struct in
> >>  	inode->i_size = 0;
> >>  
> >>  	if (insert_inode_locked(inode) < 0) {
> >> +		mutex_unlock(&f->sem);
> >>  		make_bad_inode(inode);
> >>  		iput(inode);
> >>  		return ERR_PTR(-EINVAL);

Brian