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Re: Loopback device hung [was Re: xfs deadlock on 3.9-rc5 running xfstes

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Loopback device hung [was Re: xfs deadlock on 3.9-rc5 running xfstests case #78]
From: Jens Axboe <axboe@xxxxxxxxx>
Date: Tue, 2 Apr 2013 09:30:35 +0200
Cc: CAI Qian <caiqian@xxxxxxxxxx>, xfs@xxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130402071937.GC3670@xxxxxxxxx>
References: <1462091996.435156.1364882416199.JavaMail.root@xxxxxxxxxx> <247719576.438259.1364882929749.JavaMail.root@xxxxxxxxxx> <20130402070537.GP6369@dastard> <20130402071937.GC3670@xxxxxxxxx>
On Tue, Apr 02 2013, Jens Axboe wrote:
> On Tue, Apr 02 2013, Dave Chinner wrote:
> > [Added jens Axboe to CC]
> > 
> > On Tue, Apr 02, 2013 at 02:08:49AM -0400, CAI Qian wrote:
> > > Saw on almost all the servers range from x64, ppc64 and s390x with kernel
> > > 3.9-rc5 and xfsprogs-3.1.10. Never caught this in 3.9-rc4, so looks like
> > > something new broke this. Log is here with sysrq debug info.
> > > http://people.redhat.com/qcai/stable/log
> 
> CAI Qian, can you try and back the below out and test again?

Nevermind, it's clearly that one. The below should improve the
situation, but it's not pretty. A better fix would be to allow
auto-deletion even if PART_NO_SCAN is set.

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index fe5f640..d6c5764 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1057,14 +1057,15 @@ static int loop_clr_fd(struct loop_device *lo)
                struct disk_part_iter piter;
                struct hd_struct *part;
 
-               mutex_lock_nested(&bdev->bd_mutex, 1);
-               invalidate_partition(bdev->bd_disk, 0);
-               disk_part_iter_init(&piter, bdev->bd_disk,
-                                       DISK_PITER_INCL_EMPTY);
-               while ((part = disk_part_iter_next(&piter)))
-                       delete_partition(bdev->bd_disk, part->partno);
-               disk_part_iter_exit(&piter);
-               mutex_unlock(&bdev->bd_mutex);
+               if (mutex_trylock(&bdev->bd_mutex, 1))
+                       invalidate_partition(bdev->bd_disk, 0);
+                       disk_part_iter_init(&piter, bdev->bd_disk,
+                                               DISK_PITER_INCL_EMPTY);
+                       while ((part = disk_part_iter_next(&piter)))
+                               delete_partition(bdev->bd_disk, part->partno);
+                       disk_part_iter_exit(&piter);
+                       mutex_unlock(&bdev->bd_mutex);
+               }
        }
 
        /*

-- 
Jens Axboe

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