LOOP_CLR_FD takes lo->lo_ctl_mutex and tries to remove the loop sysfs
files. Sysfs calls show() and waits for lo->lo_ctl_mutex. LOOP_CLR_FD
waits for show() to finish to remove the sysfs file.
cat /sys/class/block/loop0/loop/backing_file
mutex_lock_nested+0x176/0x350
? loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
? loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
dev_attr_show+0x1b/0x60
? sysfs_read_file+0x86/0x1a0
? __get_free_pages+0x12/0x50
sysfs_read_file+0xaf/0x1a0
ioctl(LOOP_CLR_FD):
wait_for_common+0x12c/0x180
? try_to_wake_up+0x2a0/0x2a0
wait_for_completion+0x18/0x20
sysfs_deactivate+0x178/0x180
? sysfs_addrm_finish+0x43/0x70
? sysfs_addrm_start+0x1d/0x20
sysfs_addrm_finish+0x43/0x70
sysfs_hash_and_remove+0x85/0xa0
sysfs_remove_group+0x59/0x100
loop_clr_fd+0x1dc/0x3f0 [loop]
lo_ioctl+0x223/0x7a0 [loop]
Instead of taking the lo_ctl_mutex from sysfs code, take the inner
lo->lo_lock, to protect the access to the backing_file data.
Thanks to Tejun for help debugging and finding a solution.
Cc: Milan Broz <mbroz@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Cc: stable@kernel.org
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
05eb0f252b