loop: Flush possible running bios when loop device is released.
authorMilan Broz <mbroz@redhat.com>
Fri, 12 Dec 2008 13:48:27 +0000 (14:48 +0100)
committerJens Axboe <jens.axboe@oracle.com>
Mon, 29 Dec 2008 07:29:52 +0000 (08:29 +0100)
commit14f2793958bd7878db2dc0309ed4525d6b7f1b72
tree6113ae1d21963b96e10a5174d2c3365b1f0570fd
parent10e5b64415ae9a0ba81dd1f1036d14dfdae9308c
loop: Flush possible running bios when loop device is released.

When there are still queued bios and reference count
drops to zero, loop device must flush all queued bios.

Otherwise it can lead to situation that caller
closes the device, but some bios are still running
and endio() function call later OOpses when uses
unallocated mempool.

This happens for example when running dm-crypt over loop,
here is typical oops backtrace:

 Oops: 0000 [#1] PREEMPT SMP
 EIP is at mempool_free+0x12/0x6b
...
 crypt_dec_pending+0x50/0x54 [dm_crypt]
 crypt_endio+0x9f/0xa7 [dm_crypt]
 crypt_endio+0x0/0xa7 [dm_crypt]
 bio_endio+0x2b/0x2e
 loop_thread+0x37a/0x3b1
 do_lo_send_aops+0x0/0x165
 autoremove_wake_function+0x0/0x33
 loop_thread+0x0/0x3b1
 kthread+0x3b/0x61
 kthread+0x0/0x61
 kernel_thread_helper+0x7/0x10

(But crash is reproducible with different dm targets
running over loop device too.)

Patch fixes it by flushing the bios in release call,
reusing the flush mechanism for switching backing store.

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
drivers/block/loop.c