From fd51469fb68b987032e46297e0a4fe9020063c20 Mon Sep 17 00:00:00 2001 From: Petr Uzel Date: Thu, 3 Mar 2011 11:48:50 -0500 Subject: [PATCH] block: kill loop_mutex 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: [] irq_exit+0x36/0x59 [] smp_apic_timer_interrupt+0x6b/0x75 [] apic_timer_interrupt+0x31/0x38 [] mutex_spin_on_owner+0x54/0x5b [] lo_release+0x12/0x67 [loop] [] __blkdev_put+0x7c/0x10c [] fput+0xd5/0x1aa [] loop_clr_fd+0x1a9/0x1b1 [loop] [] lo_release+0x39/0x67 [loop] [] __blkdev_put+0x7c/0x10c [] deactivate_locked_super+0x17/0x36 [] sys_umount+0x27e/0x2a5 [] sys_oldumount+0xb/0xe [] sysenter_do_call+0x12/0x26 [] 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 Signed-off-by: Petr Uzel Cc: stable@kernel.org Reviewed-by: Nikanth Karthikesan Acked-by: Arnd Bergmann Signed-off-by: Jens Axboe --- drivers/block/loop.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 49e6a545eb63..dbf31ec9114d 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -78,7 +78,6 @@ #include -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; }