* [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
@ 2011-12-17 21:53 Sergey Senozhatsky
2011-12-17 22:12 ` Al Viro
0 siblings, 1 reply; 9+ messages in thread
From: Sergey Senozhatsky @ 2011-12-17 21:53 UTC (permalink / raw)
To: Jens Axboe
Cc: Andrew Morton, Kay Sievers, Namhyung Kim, Lukas Czerner,
linux-kernel
Unmonting mounted with `-o loop' block device causes recursive
bd_mutex locking. fput() calls blkdev_put() for bdev that issued
disk->fops->release() (loop_clr_fd()) call:
[23044.654647] umount/24442 is trying to acquire lock:
[23044.654652] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81144311>] blkdev_put+0x1f/0x131
[23044.654670]
[23044.654672] but task is already holding lock:
[23044.654677] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
[23044.654690]
[23044.654692] other info that might help us debug this:
[23044.654697] Possible unsafe locking scenario:
[23044.654727]
[23044.654731] 1 lock held by umount/24442:
[23044.654735] #0: (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
[23044.654748]
[23044.654762] Call Trace:
[23044.654773] [<ffffffff81075611>] __lock_acquire+0x15bf/0x1659
[23044.654784] [<ffffffff8114b3e3>] ? inotify_free_group_priv+0x4f/0x4f
[23044.654792] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
[23044.654799] [<ffffffff81075c6a>] lock_acquire+0x138/0x1b3
[23044.654807] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
[23044.654814] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
[23044.654824] [<ffffffff8147ce67>] mutex_lock_nested+0x5e/0x325
[23044.654831] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
[23044.654838] [<ffffffff81149963>] ? fsnotify+0x441/0x459
[23044.654846] [<ffffffff81144311>] blkdev_put+0x1f/0x131
[23044.654853] [<ffffffff81144443>] blkdev_close+0x20/0x22
[23044.654863] [<ffffffff81116b21>] fput+0x117/0x1cf
[23044.654874] [<ffffffffa016eb71>] loop_clr_fd+0x1f2/0x201 [loop]
[23044.654882] [<ffffffffa016f861>] lo_release+0x40/0x6f [loop]
[23044.654890] [<ffffffff81144244>] __blkdev_put+0xd6/0x184
[23044.654898] [<ffffffff8114441a>] blkdev_put+0x128/0x131
[23044.654906] [<ffffffff8111704e>] kill_block_super+0x60/0x65
[23044.654914] [<ffffffff81117366>] deactivate_locked_super+0x32/0x63
[23044.654922] [<ffffffff81117cc9>] deactivate_super+0x3a/0x3e
[23044.654931] [<ffffffff8112fc5d>] mntput_no_expire+0xbf/0xc4
[23044.654939] [<ffffffff811309c7>] sys_umount+0x2c5/0x2f3
[23044.654949] [<ffffffff81484b12>] system_call_fastpath+0x16/0x1b
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 1e888c9..b004779 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1028,6 +1028,15 @@ static int loop_clr_fd(struct loop_device *lo)
* lock dependency possibility warning as fput can take
* bd_mutex which is usually taken before lo_ctl_mutex.
*/
+ /*
+ * Need to put file f_op, otherwise fput() may cause
+ * recursive locking on bd_mutex, calling blkdev_put()
+ * for bdev that issued disk->fops->release() call.
+ */
+ if (bdev && bdev == bdev->bd_contains) {
+ fops_put(filp->f_op);
+ filp->f_op = NULL;
+ }
fput(filp);
return 0;
}
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 21:53 [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking Sergey Senozhatsky
@ 2011-12-17 22:12 ` Al Viro
2011-12-17 22:19 ` Sergey Senozhatsky
0 siblings, 1 reply; 9+ messages in thread
From: Al Viro @ 2011-12-17 22:12 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Jens Axboe, Andrew Morton, Kay Sievers, Namhyung Kim,
Lukas Czerner, linux-kernel
On Sun, Dec 18, 2011 at 12:53:33AM +0300, Sergey Senozhatsky wrote:
> Unmonting mounted with `-o loop' block device causes recursive
> bd_mutex locking. fput() calls blkdev_put() for bdev that issued
> disk->fops->release() (loop_clr_fd()) call:
>
> [23044.654647] umount/24442 is trying to acquire lock:
> [23044.654652] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81144311>] blkdev_put+0x1f/0x131
> [23044.654670]
> [23044.654672] but task is already holding lock:
> [23044.654677] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
> [23044.654690]
> [23044.654692] other info that might help us debug this:
> [23044.654697] Possible unsafe locking scenario:
> [23044.654727]
> [23044.654731] 1 lock held by umount/24442:
> [23044.654735] #0: (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
> [23044.654748]
> [23044.654762] Call Trace:
> [23044.654773] [<ffffffff81075611>] __lock_acquire+0x15bf/0x1659
> [23044.654784] [<ffffffff8114b3e3>] ? inotify_free_group_priv+0x4f/0x4f
> [23044.654792] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> [23044.654799] [<ffffffff81075c6a>] lock_acquire+0x138/0x1b3
> [23044.654807] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> [23044.654814] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> [23044.654824] [<ffffffff8147ce67>] mutex_lock_nested+0x5e/0x325
> [23044.654831] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> [23044.654838] [<ffffffff81149963>] ? fsnotify+0x441/0x459
> [23044.654846] [<ffffffff81144311>] blkdev_put+0x1f/0x131
> [23044.654853] [<ffffffff81144443>] blkdev_close+0x20/0x22
> [23044.654863] [<ffffffff81116b21>] fput+0x117/0x1cf
> [23044.654874] [<ffffffffa016eb71>] loop_clr_fd+0x1f2/0x201 [loop]
> [23044.654882] [<ffffffffa016f861>] lo_release+0x40/0x6f [loop]
> [23044.654890] [<ffffffff81144244>] __blkdev_put+0xd6/0x184
> [23044.654898] [<ffffffff8114441a>] blkdev_put+0x128/0x131
> [23044.654906] [<ffffffff8111704e>] kill_block_super+0x60/0x65
> [23044.654914] [<ffffffff81117366>] deactivate_locked_super+0x32/0x63
> [23044.654922] [<ffffffff81117cc9>] deactivate_super+0x3a/0x3e
> [23044.654931] [<ffffffff8112fc5d>] mntput_no_expire+0xbf/0xc4
> [23044.654939] [<ffffffff811309c7>] sys_umount+0x2c5/0x2f3
> [23044.654949] [<ffffffff81484b12>] system_call_fastpath+0x16/0x1b
>
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
>
> ---
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 1e888c9..b004779 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1028,6 +1028,15 @@ static int loop_clr_fd(struct loop_device *lo)
> * lock dependency possibility warning as fput can take
> * bd_mutex which is usually taken before lo_ctl_mutex.
> */
> + /*
> + * Need to put file f_op, otherwise fput() may cause
> + * recursive locking on bd_mutex, calling blkdev_put()
> + * for bdev that issued disk->fops->release() call.
> + */
> + if (bdev && bdev == bdev->bd_contains) {
> + fops_put(filp->f_op);
> + filp->f_op = NULL;
> + }
> fput(filp);
> return 0;
> }
NAK - you've "fixed" a false positive from lock checker by failing to close
the underlying device.
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 22:12 ` Al Viro
@ 2011-12-17 22:19 ` Sergey Senozhatsky
2011-12-17 22:30 ` Al Viro
0 siblings, 1 reply; 9+ messages in thread
From: Sergey Senozhatsky @ 2011-12-17 22:19 UTC (permalink / raw)
To: Al Viro
Cc: Sergey Senozhatsky, Jens Axboe, Andrew Morton, Kay Sievers,
Namhyung Kim, Lukas Czerner, linux-kernel
On (12/17/11 22:12), Al Viro wrote:
> >
> > [23044.654647] umount/24442 is trying to acquire lock:
> > [23044.654652] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81144311>] blkdev_put+0x1f/0x131
> > [23044.654670]
> > [23044.654672] but task is already holding lock:
> > [23044.654677] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
> > [23044.654690]
> > [23044.654692] other info that might help us debug this:
> > [23044.654697] Possible unsafe locking scenario:
> > [23044.654727]
> > [23044.654731] 1 lock held by umount/24442:
> > [23044.654735] #0: (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
> > [23044.654748]
> > [23044.654762] Call Trace:
> > [23044.654773] [<ffffffff81075611>] __lock_acquire+0x15bf/0x1659
> > [23044.654784] [<ffffffff8114b3e3>] ? inotify_free_group_priv+0x4f/0x4f
> > [23044.654792] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654799] [<ffffffff81075c6a>] lock_acquire+0x138/0x1b3
> > [23044.654807] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654814] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654824] [<ffffffff8147ce67>] mutex_lock_nested+0x5e/0x325
> > [23044.654831] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654838] [<ffffffff81149963>] ? fsnotify+0x441/0x459
> > [23044.654846] [<ffffffff81144311>] blkdev_put+0x1f/0x131
> > [23044.654853] [<ffffffff81144443>] blkdev_close+0x20/0x22
> > [23044.654863] [<ffffffff81116b21>] fput+0x117/0x1cf
> > [23044.654874] [<ffffffffa016eb71>] loop_clr_fd+0x1f2/0x201 [loop]
> > [23044.654882] [<ffffffffa016f861>] lo_release+0x40/0x6f [loop]
> > [23044.654890] [<ffffffff81144244>] __blkdev_put+0xd6/0x184
> > [23044.654898] [<ffffffff8114441a>] blkdev_put+0x128/0x131
> > [23044.654906] [<ffffffff8111704e>] kill_block_super+0x60/0x65
> > [23044.654914] [<ffffffff81117366>] deactivate_locked_super+0x32/0x63
> > [23044.654922] [<ffffffff81117cc9>] deactivate_super+0x3a/0x3e
> > [23044.654931] [<ffffffff8112fc5d>] mntput_no_expire+0xbf/0xc4
> > [23044.654939] [<ffffffff811309c7>] sys_umount+0x2c5/0x2f3
> > [23044.654949] [<ffffffff81484b12>] system_call_fastpath+0x16/0x1b
[..]
>
> NAK - you've "fixed" a false positive from lock checker by failing to close
> the underlying device.
>
Sorry, why is that a false positive?
blkdev_put() calls lo_release() while holding bd_mutex,
lo_release() calls loop_clr_fd() -> fput(). fput() once again
attempts to grub already held bd_mutex calling blkdev_put().
Looks like a recursion to me.
Sergey
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 22:19 ` Sergey Senozhatsky
@ 2011-12-17 22:30 ` Al Viro
2011-12-17 22:37 ` Sergey Senozhatsky
0 siblings, 1 reply; 9+ messages in thread
From: Al Viro @ 2011-12-17 22:30 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Jens Axboe, Andrew Morton, Kay Sievers, Namhyung Kim,
Lukas Czerner, linux-kernel
On Sun, Dec 18, 2011 at 01:19:28AM +0300, Sergey Senozhatsky wrote:
> Sorry, why is that a false positive?
>
> blkdev_put() calls lo_release() while holding bd_mutex,
> lo_release() calls loop_clr_fd() -> fput(). fput() once again
> attempts to grub already held bd_mutex calling blkdev_put().
> Looks like a recursion to me.
Because of this:
/* Avoid recursion */
f = file;
while (is_loop_device(f)) {
struct loop_device *l;
if (f->f_mapping->host->i_bdev == bdev)
goto out_putf;
l = f->f_mapping->host->i_bdev->bd_disk->private_data;
if (l->lo_state == Lo_unbound) {
error = -EINVAL;
goto out_putf;
}
f = l->lo_backing_file;
}
in loop_set_fd(). Think of it for a minute - if we could run into the
same bdev in that recursion, what would have happened on read() from
that sucker? So yes, it is a false positive. And your patch would
simply leave the underlying device opened, with all the consequences...
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 22:30 ` Al Viro
@ 2011-12-17 22:37 ` Sergey Senozhatsky
2011-12-17 22:58 ` Al Viro
0 siblings, 1 reply; 9+ messages in thread
From: Sergey Senozhatsky @ 2011-12-17 22:37 UTC (permalink / raw)
To: Al Viro
Cc: Sergey Senozhatsky, Jens Axboe, Andrew Morton, Kay Sievers,
Namhyung Kim, Lukas Czerner, linux-kernel
On (12/17/11 22:30), Al Viro wrote:
> > Sorry, why is that a false positive?
> >
> > blkdev_put() calls lo_release() while holding bd_mutex,
> > lo_release() calls loop_clr_fd() -> fput(). fput() once again
> > attempts to grub already held bd_mutex calling blkdev_put().
> > Looks like a recursion to me.
>
> Because of this:
> /* Avoid recursion */
> f = file;
> while (is_loop_device(f)) {
> struct loop_device *l;
>
> if (f->f_mapping->host->i_bdev == bdev)
> goto out_putf;
>
> l = f->f_mapping->host->i_bdev->bd_disk->private_data;
> if (l->lo_state == Lo_unbound) {
> error = -EINVAL;
> goto out_putf;
> }
> f = l->lo_backing_file;
> }
> in loop_set_fd().
Oh, thanks. I didn't notice that one.
> Think of it for a minute - if we could run into the
> same bdev in that recursion, what would have happened on read() from
> that sucker? So yes, it is a false positive.
I've tried read()/write() some time ago and it worked. Perhaps, I just
wasn't "lucky" enough to hit any problems.
> And your patch would simply leave the underlying device opened,
> with all the consequences...
>
well, that sucks.
Sergey
^ permalink raw reply [flat|nested] 9+ messages in thread* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 22:37 ` Sergey Senozhatsky
@ 2011-12-17 22:58 ` Al Viro
2011-12-17 23:20 ` Sergey Senozhatsky
0 siblings, 1 reply; 9+ messages in thread
From: Al Viro @ 2011-12-17 22:58 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Jens Axboe, Andrew Morton, Kay Sievers, Namhyung Kim,
Lukas Czerner, linux-kernel
On Sun, Dec 18, 2011 at 01:37:45AM +0300, Sergey Senozhatsky wrote:
> > Think of it for a minute - if we could run into the
> > same bdev in that recursion, what would have happened on read() from
> > that sucker? So yes, it is a false positive.
>
> I've tried read()/write() some time ago and it worked. Perhaps, I just
> wasn't "lucky" enough to hit any problems.
Sure - exactly because of that loop prevention logics. *If* we really
had been able to set a loop0 -> loop1 -> loop2 -> loop0 or something of
that sort, this warning wouldn't be a false positive. But on any
such setup, where would IO attempts end up doing? IOW, we have to
prevent such setups anyway and not just because of problems on close() -
they would be deadly on read() and write()...
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 22:58 ` Al Viro
@ 2011-12-17 23:20 ` Sergey Senozhatsky
2011-12-17 23:38 ` Al Viro
0 siblings, 1 reply; 9+ messages in thread
From: Sergey Senozhatsky @ 2011-12-17 23:20 UTC (permalink / raw)
To: Al Viro
Cc: Sergey Senozhatsky, Jens Axboe, Andrew Morton, Kay Sievers,
Namhyung Kim, Lukas Czerner, linux-kernel
On (12/17/11 22:58), Al Viro wrote:
> On Sun, Dec 18, 2011 at 01:37:45AM +0300, Sergey Senozhatsky wrote:
> > > Think of it for a minute - if we could run into the
> > > same bdev in that recursion, what would have happened on read() from
> > > that sucker? So yes, it is a false positive.
> >
> > I've tried read()/write() some time ago and it worked. Perhaps, I just
> > wasn't "lucky" enough to hit any problems.
>
> Sure - exactly because of that loop prevention logics. *If* we really
> had been able to set a loop0 -> loop1 -> loop2 -> loop0 or something of
> that sort, this warning wouldn't be a false positive. But on any
> such setup, where would IO attempts end up doing?
Thanks for your explanations.
> IOW, we have to prevent such setups anyway and not just because of
> problems on close() - they would be deadly on read() and write()...
>
Preventing recursion in the first place? For example, in lo_open()?
Sergey
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 23:20 ` Sergey Senozhatsky
@ 2011-12-17 23:38 ` Al Viro
2011-12-17 23:47 ` Sergey Senozhatsky
0 siblings, 1 reply; 9+ messages in thread
From: Al Viro @ 2011-12-17 23:38 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Jens Axboe, Andrew Morton, Kay Sievers, Namhyung Kim,
Lukas Czerner, linux-kernel
On Sun, Dec 18, 2011 at 02:20:53AM +0300, Sergey Senozhatsky wrote:
> > IOW, we have to prevent such setups anyway and not just because of
> > problems on close() - they would be deadly on read() and write()...
> >
>
> Preventing recursion in the first place? For example, in lo_open()?
Uh? No, in loop_set_fd(), where we decide what loop devices will be
backed by what - the code I quoted to you upthread.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
2011-12-17 23:38 ` Al Viro
@ 2011-12-17 23:47 ` Sergey Senozhatsky
0 siblings, 0 replies; 9+ messages in thread
From: Sergey Senozhatsky @ 2011-12-17 23:47 UTC (permalink / raw)
To: Al Viro
Cc: Sergey Senozhatsky, Jens Axboe, Andrew Morton, Kay Sievers,
Namhyung Kim, Lukas Czerner, linux-kernel
On (12/17/11 23:38), Al Viro wrote:
> On Sun, Dec 18, 2011 at 02:20:53AM +0300, Sergey Senozhatsky wrote:
>
> > > IOW, we have to prevent such setups anyway and not just because of
> > > problems on close() - they would be deadly on read() and write()...
> > >
> >
> > Preventing recursion in the first place? For example, in lo_open()?
>
> Uh? No, in loop_set_fd(), where we decide what loop devices will be
> backed by what - the code I quoted to you upthread.
>
Oops, sorry. Long day at work . Need to sleep.
Sergey
^ permalink raw reply [flat|nested] 9+ messages in thread
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2011-12-17 21:53 [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking Sergey Senozhatsky
2011-12-17 22:12 ` Al Viro
2011-12-17 22:19 ` Sergey Senozhatsky
2011-12-17 22:30 ` Al Viro
2011-12-17 22:37 ` Sergey Senozhatsky
2011-12-17 22:58 ` Al Viro
2011-12-17 23:20 ` Sergey Senozhatsky
2011-12-17 23:38 ` Al Viro
2011-12-17 23:47 ` Sergey Senozhatsky
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