linux-kernel - Re: Regression in next with ext4 oops

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Message-ID: <20161005054445.GA20752@quack2.suse.cz>
Date:   Wed, 5 Oct 2016 07:44:45 +0200
From:   Jan Kara <jack@...e.cz>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Jan Kara <jack@...e.cz>, Tony Lindgren <tony@...mide.com>,
        Eric Biggers <ebiggers@...gle.com>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger@...ger.ca>,
        Jaegeuk Kim <jaegeuk@...nel.org>, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org
Subject: Re: Regression in next with ext4 oops

On Tue 04-10-16 15:56:39, Al Viro wrote:
> On Tue, Oct 04, 2016 at 11:00:41AM +0200, Jan Kara wrote:
> > Hi!
> > 
> > On Mon 03-10-16 16:30:55, Tony Lindgren wrote:
> > > I'm seeing a repeatable oops with Linux next while running
> > > update-initramfs, see below. I tried reverting commit 59aa5a3aeead
> > > ("fscrypto: make filename crypto functions return 0 on success")
> > > as that's the only commit changing ext4_htree_store_dirent, but
> > > that did not help.
> > > 
> > > Anybody else seeing something like this?
> > 
> > Never seen this but I suspect it is a fallout from Al's directory locking
> > changes. In particular ext4_htree_fill_tree() builds rb-tree of found
> > directory entries in file->private_data (and generally modifies the
> > structure stored there) but after Al's changes we don't have exclusive
> > access to struct file if I'm right so if two processes end up calling
> > getdents() for the same 'struct file' we are doomed.
> 
> RTFS.  We sure as hell *do* have exclusive access to struct file.  See
>         /* POSIX.1-2008/SUSv4 Section XSI 2.9.7 */
>         if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))
>                 f->f_mode |= FMODE_ATOMIC_POS;
> in do_dentry_open() as well as
>         if (file && (file->f_mode & FMODE_ATOMIC_POS)) {
>                 if (file_count(file) > 1) {
>                         v |= FDPUT_POS_UNLOCK;
>                         mutex_lock(&file->f_pos_lock);
>                 }
>         }
> in __fdget_pos() and
>         f = fdget_pos(fd);
>         if (!f.file)
>                 return -EBADF;
> in getdents(2).

Yeah, sorry. I've misunderstood how the FMODE_ATOMIC_POS thing works...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR