[PATCH 4.9 066/153] block/loop: fix race between I/O and set_status

Greg Kroah-Hartman
2017-03-10T09:22:50Z

From: Ming Lei <tom.leiming@gmail.com>

commit ecdd09597a57251323b0de50e3d45e69298c4a83 upstream.

Inside set_status, transfer need to setup again, so
we have to drain IO before the transition, otherwise
oops may be triggered like the following:

divide error: 0000 [#1] SMP KASAN
CPU: 0 PID: 2935 Comm: loop7 Not tainted 4.10.0-rc7+ #213
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
01/01/2011
task: ffff88006ba1e840 task.stack: ffff880067338000
RIP: 0010:transfer_xor+0x1d1/0x440 drivers/block/loop.c:110
RSP: 0018:ffff88006733f108 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8800688d7000 RCX: 0000000000000059
RDX: 0000000000000000 RSI: 1ffff1000d743f43 RDI: ffff880068891c08
RBP: ffff88006733f160 R08: ffff8800688d7001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800688d7000
R13: ffff880067b7d000 R14: dffffc0000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88006d000000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000006c17e0 CR3: 0000000066e3b000 CR4: 00000000001406f0
Call Trace:
lo_do_transfer drivers/block/loop.c:251 [inline]
lo_read_transfer drivers/block/loop.c:392 [inline]
do_req_filebacked drivers/block/loop.c:541 [inline]
loop_handle_cmd drivers/block/loop.c:1677 [inline]
loop_queue_work+0xda0/0x49b0 drivers/block/loop.c:1689
kthread_worker_fn+0x4c3/0xa30 kernel/kthread.c:630
kthread+0x326/0x3f0 kernel/kthread.c:227
ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
Code: 03 83 e2 07 41 29 df 42 0f b6 04 30 4d 8d 44 24 01 38 d0 7f 08
84 c0 0f 85 62 02 00 00 44 89 f8 41 0f b6 48 ff 25 ff 01 00 00 99 <f7>
7d c8 48 63 d2 48 03 55 d0 48 89 d0 48 89 d7 48 c1 e8 03 83
RIP: transfer_xor+0x1d1/0x440 drivers/block/loop.c:110 RSP:
ffff88006733f108
---[ end trace 0166f7bd3b0c0933 ]---

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/loop.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1097,9 +1097,12 @@ loop_set_status(struct loop_device *lo,
if ((unsigned int) info->lo_encrypt_key_size > LO_KEY_SIZE)
return -EINVAL;

+ /* I/O need to be drained during transfer transition */
+ blk_mq_freeze_queue(lo->lo_queue);
+
err = loop_release_xfer(lo);
if (err)
- return err;
+ goto exit;

if (info->lo_encrypt_type) {
unsigned int type = info->lo_encrypt_type;
@@ -1114,12 +1117,14 @@ loop_set_status(struct loop_device *lo,

err = loop_init_xfer(lo, xfer, info);
if (err)
- return err;
+ goto exit;

if (lo->lo_offset != info->lo_offset ||
lo->lo_sizelimit != info->lo_sizelimit)
- if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit))
- return -EFBIG;
+ if (figure_loop_size(lo, info->lo_offset, info->lo_sizelimit)) {
+ err = -EFBIG;
+ goto exit;
+ }

loop_config_discard(lo);

@@ -1156,7 +1161,9 @@ loop_set_status(struct loop_device *lo,
/* update dio if lo_offset or transfer is changed */
__loop_update_dio(lo, lo->use_dio);

- return 0;
+ exit:
+ blk_mq_unfreeze_queue(lo->lo_queue);
+ return err;
}

static int