Re: [PATCH] block/loop: fix race between I/O and set_status

[Jens Axboe]

On 02/10/2017 08:40 PM, Ming Lei wrote:
> 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 ]---

Thanks Ming, added for 4.11.

-- 
Jens Axboe