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From: Al Viro <[email protected]>
To: Christian Brauner <[email protected]>
Cc: Jens Axboe <[email protected]>,
	syzbot <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [syzbot] WARNING in mntput_no_expire (2)
Date: Mon, 5 Apr 2021 18:28:54 +0000	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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(&current->fs->lock);
> WARN_ON(d_count(current->fs->pwd.dentry) < 0);
> spin_unlock(&current->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)) {

  reply	other threads:[~2021-04-05 18:29 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
2021-04-01 15:45 ` [syzbot] WARNING in mntput_no_expire (2) 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 [this message]
2021-04-05 20:07                                     ` Christian Brauner
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

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