From: Christian Brauner <christian.brauner@ubuntu.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>,
syzbot <syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
syzkaller-bugs@googlegroups.com, io-uring@vger.kernel.org
Subject: Re: [syzbot] WARNING in mntput_no_expire (2)
Date: Mon, 5 Apr 2021 22:07:37 +0200 [thread overview]
Message-ID: <20210405200737.qurhkqitoxweousx@wittgenstein> (raw)
In-Reply-To: <YGtW5g6EFFArtevk@zeniv-ca.linux.org.uk>
On Mon, Apr 05, 2021 at 06:28:54PM +0000, Al Viro wrote:
> On Mon, Apr 05, 2021 at 06:23:49PM +0000, Al Viro wrote:
> > On Mon, Apr 05, 2021 at 07:08:01PM +0200, Christian Brauner wrote:
> >
> > > Ah dentry count of -127 looks... odd.
> >
> > dead + 1...
> >
> > void lockref_mark_dead(struct lockref *lockref)
> > {
> > assert_spin_locked(&lockref->lock);
> > lockref->count = -128;
> > }
> >
> > IOW, a leaked (uncounted) reference to dentry, that got dget() called on
> > it after dentry had been freed.
> >
> > IOW, current->fs->pwd.dentry happens to point to an already freed
> > struct dentry here. Joy...
> >
> > Could you slap
> >
> > spin_lock(¤t->fs->lock);
> > WARN_ON(d_count(current->fs->pwd.dentry) < 0);
> > spin_unlock(¤t->fs->lock);
> >
> > before and after calls of io_issue_sqe() and see if it triggers? We definitely
> > are seeing buggered dentry refcounting here.
>
> Check if this helps, please.
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 216f16e74351..82344f1139ff 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -2289,6 +2289,9 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
> int error;
> const char *s = nd->name->name;
>
> + nd->path.mnt = NULL;
> + nd->path.dentry = NULL;
> +
> /* LOOKUP_CACHED requires RCU, ask caller to retry */
> if ((flags & (LOOKUP_RCU | LOOKUP_CACHED)) == LOOKUP_CACHED)
> return ERR_PTR(-EAGAIN);
> @@ -2322,8 +2325,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
> }
>
> nd->root.mnt = NULL;
> - nd->path.mnt = NULL;
> - nd->path.dentry = NULL;
>
> /* Absolute pathname -- fetch the root (LOOKUP_IN_ROOT uses nd->dfd). */
> if (*s == '/' && !(flags & LOOKUP_IN_ROOT)) {
Bingo. That fixes it.
next prev parent reply other threads:[~2021-04-05 20:07 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-01 9:09 [syzbot] WARNING in mntput_no_expire (2) syzbot
2021-04-01 12:16 ` syzbot
2021-04-01 18:32 ` Christian Brauner
2021-04-01 15:45 ` Christian Brauner
2021-04-01 16:09 ` Jens Axboe
2021-04-01 17:46 ` Christian Brauner
2021-04-01 17:59 ` Christian Brauner
2021-04-01 19:11 ` Al Viro
2021-04-04 2:34 ` Al Viro
2021-04-04 2:38 ` Al Viro
2021-04-04 11:34 ` Christian Brauner
2021-04-04 15:56 ` Al Viro
2021-04-04 16:40 ` Christian Brauner
2021-04-04 16:44 ` Al Viro
2021-04-04 17:05 ` Christian Brauner
2021-04-04 18:50 ` Al Viro
2021-04-04 20:17 ` Al Viro
2021-04-05 11:44 ` Christian Brauner
2021-04-05 16:18 ` Al Viro
2021-04-05 17:08 ` Christian Brauner
2021-04-05 18:23 ` Al Viro
2021-04-05 18:28 ` Al Viro
2021-04-05 20:07 ` Christian Brauner [this message]
2021-04-06 1:38 ` Al Viro
2021-04-06 2:24 ` Al Viro
2021-04-06 12:35 ` Christian Brauner
2021-04-06 13:13 ` Al Viro
2021-04-06 13:22 ` Christian Brauner
2021-04-06 14:15 ` Al Viro
2021-04-06 14:23 ` Al Viro
2021-04-06 15:37 ` Jens Axboe
2021-04-06 14:46 ` Christian Brauner
2021-04-04 16:52 ` Christian Brauner
2021-04-04 16:55 ` Christian Brauner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210405200737.qurhkqitoxweousx@wittgenstein \
--to=christian.brauner@ubuntu.com \
--cc=axboe@kernel.dk \
--cc=io-uring@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).