On Friday, February 25, 2011 07:57:29 pm Petr Uzel wrote: > Following steps lead to deadlock in kernel: > > dd if=/dev/zero of=img bs=512 count=1000 > losetup -f img > mkfs.ext2 /dev/loop0 > mount -t ext2 -o loop /dev/loop0 mnt > umount mnt/ > > Stacktrace: > [<c102ec04>] irq_exit+0x36/0x59 > [<c101502c>] smp_apic_timer_interrupt+0x6b/0x75 > [<c127f639>] apic_timer_interrupt+0x31/0x38 > [<c101df88>] mutex_spin_on_owner+0x54/0x5b > [<fe2250e9>] lo_release+0x12/0x67 [loop] > [<c10c4eae>] __blkdev_put+0x7c/0x10c > [<c10a4da5>] fput+0xd5/0x1aa > [<fe2250cf>] loop_clr_fd+0x1a9/0x1b1 [loop] > [<fe225110>] lo_release+0x39/0x67 [loop] > [<c10c4eae>] __blkdev_put+0x7c/0x10c > [<c10a59d9>] deactivate_locked_super+0x17/0x36 > [<c10b6f37>] sys_umount+0x27e/0x2a5 > [<c10b6f69>] sys_oldumount+0xb/0xe > [<c1002897>] sysenter_do_call+0x12/0x26 > [<ffffffff>] 0xffffffff > > Regression since 2a48fc0ab24241755dc9, which introduced the private > loop_mutex as part of the BKL removal process. > > As per [1], the mutex can be safely removed. > > [1] http://www.gossamer-threads.com/lists/linux/kernel/1341930 > > Addresses: https://bugzilla.novell.com/show_bug.cgi?id=669394 > Addresses: https://bugzilla.kernel.org/show_bug.cgi?id=29172 >
BKL was recursive, but the loop_mutex is not, which results in the hang during umount in case of loop over loop with LO_FLAGS_AUTOCLEAR . And I don't see any need for loop_mutex. > Signed-off-by: Petr Uzel <[email protected]> Reviewed-by: Nikanth Karthikesan <[email protected]> > --- > drivers/block/loop.c | 5 ----- > 1 files changed, 0 insertions(+), 5 deletions(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 49e6a54..dbf31ec 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -78,7 +78,6 @@ > > #include <asm/uaccess.h> > > -static DEFINE_MUTEX(loop_mutex); > static LIST_HEAD(loop_devices); > static DEFINE_MUTEX(loop_devices_mutex); > > @@ -1501,11 +1500,9 @@ static int lo_open(struct block_device *bdev, > fmode_t mode) { > struct loop_device *lo = bdev->bd_disk->private_data; > > - mutex_lock(&loop_mutex); > mutex_lock(&lo->lo_ctl_mutex); > lo->lo_refcnt++; > mutex_unlock(&lo->lo_ctl_mutex); > - mutex_unlock(&loop_mutex); > > return 0; > } > @@ -1515,7 +1512,6 @@ static int lo_release(struct gendisk *disk, fmode_t > mode) struct loop_device *lo = disk->private_data; > int err; > > - mutex_lock(&loop_mutex); > mutex_lock(&lo->lo_ctl_mutex); > > if (--lo->lo_refcnt) > @@ -1540,7 +1536,6 @@ static int lo_release(struct gendisk *disk, fmode_t > mode) out: > mutex_unlock(&lo->lo_ctl_mutex); > out_unlocked: > - mutex_unlock(&loop_mutex); > return 0; > } _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
