Re: loop: divide error in transfer_xor
From: Ming Lei
Date: Wed Feb 08 2017 - 05:50:53 EST
On Wed, Feb 8, 2017 at 5:32 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
> Hello,
>
> The following program triggers divide error in transfer_xor:
> https://gist.githubusercontent.com/dvyukov/bed5c929410b5619ff491c7ab22ae3f8/raw/69756a281ea0057799943412e60b8256b9f1af73/gistfile1.txt
>
> 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 ]---
>
> On commit 8b1b41ee74f9712c355d66dc105bbea663ae0afd
Looks a race between set status and I/O, could you test the attached
patch to see if this oops can be fixed?
Thanksï
Ming Lei
From 38fc4fdabfb342c1ca10bacc095a40ba5c729acc Mon Sep 17 00:00:00 2001
From: Ming Lei <tom.leiming@xxxxxxxxx>
Date: Wed, 8 Feb 2017 18:08:46 +0800
Subject: [PATCH] block/loop: fix race between I/O and set_status
During set status, transfer will be setup again, so
we need 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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx>
---
drivers/block/loop.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ed5259510857..4b52a1690329 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1097,9 +1097,12 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
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, const struct loop_info64 *info)
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, const struct loop_info64 *info)
/* 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
--
2.7.4