On 12/01/2016 01:18 AM, Jan Kara wrote:
> From: Rabin Vincent <rab...@axis.com>
> 
> If a block device is closed while iterate_bdevs() is handling it, the
> following NULL pointer dereference occurs because bdev->b_disk is NULL
> in bdev_get_queue(), which is called from blk_get_backing_dev_info() (in
> turn called by the mapping_cap_writeback_dirty() call in
> __filemap_fdatawrite_range()):
> 
>  BUG: unable to handle kernel NULL pointer dereference at 0000000000000508
>  IP: [<ffffffff81314790>] blk_get_backing_dev_info+0x10/0x20
>  PGD 9e62067 PUD 9ee8067 PMD 0
>  Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
>  Modules linked in:
>  CPU: 1 PID: 2422 Comm: sync Not tainted 4.5.0-rc7+ #400
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
>  task: ffff880009f4d700 ti: ffff880009f5c000 task.ti: ffff880009f5c000
>  RIP: 0010:[<ffffffff81314790>]  [<ffffffff81314790>] 
> blk_get_backing_dev_info+0x10/0x20
>  RSP: 0018:ffff880009f5fe68  EFLAGS: 00010246
>  RAX: 0000000000000000 RBX: ffff88000ec17a38 RCX: ffffffff81a4e940
>  RDX: 7fffffffffffffff RSI: 0000000000000000 RDI: ffff88000ec176c0
>  RBP: ffff880009f5fe68 R08: 0000000000000000 R09: 0000000000000000
>  R10: 0000000000000001 R11: 0000000000000000 R12: ffff88000ec17860
>  R13: ffffffff811b25c0 R14: ffff88000ec178e0 R15: ffff88000ec17a38
>  FS:  00007faee505d700(0000) GS:ffff88000fb00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>  CR2: 0000000000000508 CR3: 0000000009e8a000 CR4: 00000000000006e0
>  Stack:
>   ffff880009f5feb8 ffffffff8112e7f5 0000000000000000 7fffffffffffffff
>   0000000000000000 0000000000000000 7fffffffffffffff 0000000000000001
>   ffff88000ec178e0 ffff88000ec17860 ffff880009f5fec8 ffffffff8112e81f
>  Call Trace:
>   [<ffffffff8112e7f5>] __filemap_fdatawrite_range+0x85/0x90
>   [<ffffffff8112e81f>] filemap_fdatawrite+0x1f/0x30
>   [<ffffffff811b25d6>] fdatawrite_one_bdev+0x16/0x20
>   [<ffffffff811bc402>] iterate_bdevs+0xf2/0x130
>   [<ffffffff811b2763>] sys_sync+0x63/0x90
>   [<ffffffff815d4272>] entry_SYSCALL_64_fastpath+0x12/0x76
>  Code: 0f 1f 44 00 00 48 8b 87 f0 00 00 00 55 48 89 e5 <48> 8b 80 08 05 00 00 
> 5d
>  RIP  [<ffffffff81314790>] blk_get_backing_dev_info+0x10/0x20
>   RSP <ffff880009f5fe68>
>  CR2: 0000000000000508
>  ---[ end trace 2487336ceb3de62d ]---
> 
> The crash is easily reproducible by running the following command, if an
> msleep(100) is inserted before the call to func() in iterate_devs():
> 
>  while :; do head -c1 /dev/nullb0; done > /dev/null & while :; do sync; done
> 
> Fix it by holding the bd_mutex across the func() call and only calling
> func() if the bdev is opened.

I've added this to the 4.10 branch since it's a bit late in the cycle,
and the regression is really old.

-- 
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-block" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Reply via email to