Re: Loopback device hung [was Re: xfs deadlock on 3.9-rc5 running xfstests case #78]

[CAI Qian <caiqian@redhat.com>]

----- Original Message -----
> From: "Jens Axboe" <axboe@kernel.dk>
> To: "Dave Chinner" <david@fromorbit.com>
> Cc: "CAI Qian" <caiqian@redhat.com>, xfs@oss.sgi.com, "LKML" <linux-kernel@vger.kernel.org>
> Sent: Tuesday, April 2, 2013 3:30:35 PM
> Subject: Re: Loopback device hung [was Re: xfs deadlock on 3.9-rc5 running xfstests case #78]
> 
> 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.
Jens, when compiled the mainline (up to fefcdbe) with this patch,
it error-ed out,

drivers/block/loop.c: In function ‘loop_clr_fd’:
drivers/block/loop.c:1067:3: error: too many arguments to function ‘mutex_trylock’
In file included from include/linux/notifier.h:13:0,
                 from include/linux/memory_hotplug.h:6,
                 from include/linux/mmzone.h:771,
                 from include/linux/gfp.h:4,
                 from include/linux/kmod.h:22,
                 from include/linux/module.h:13,
                 from drivers/block/loop.c:52:
include/linux/mutex.h:168:12: note: declared here
drivers/block/loop.c: At top level:
drivers/block/loop.c:1084:2: warning: data definition has no type or storage class [enabled by default]
drivers/block/loop.c:1084:2: warning: type defaults to ‘int’ in declaration of ‘fput’ [-Wimplicit-int]
drivers/block/loop.c:1084:2: warning: parameter names (without types) in function declaration [enabled by default]
drivers/block/loop.c:1084:2: error: conflicting types for ‘fput’
In file included from drivers/block/loop.c:56:0:
include/linux/file.h:14:13: note: previous declaration of ‘fput’ was here
drivers/block/loop.c:1085:2: error: expected identifier or ‘(’ before ‘return’
drivers/block/loop.c:1086:1: error: expected identifier or ‘(’ before ‘}’ token
  CC      crypto/gf128mul.o
  CC      lib/sort.o
drivers/block/loop.c: In function ‘loop_clr_fd’:
drivers/block/loop.c:1076:2: warning: control reaches end of non-void function [-Wreturn-type]
  CC      lib/parser.o
  CC [M]  sound/pci/atiixp.o
make[2]: *** [drivers/block/loop.o] Error 1

CAI Qian
> 
> 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
> 
>