On 12/10/19 12:02 PM, Logan Gunthorpe wrote:
>
>
> On 2019-12-10 11:59 a.m., Jens Axboe wrote:
>> On 12/10/19 11:47 AM, Logan Gunthorpe wrote:
>>> The IDE driver creates some passthru requests which never get
>>> submitted to the block layer in such a way that blk_account_io_start()
>>> gets called. However, the driver still calls __blk_mq_end_request() in
>>> ide_end_rq() which will call blk_account_io_completion() which tries
>>> to dereferences req->part which is never set. See ide_prep_sense() for
>>> an example of where these requests come from.
>>>
>>> To fix this, blk_account_io_completion() and blk_account_io_done()
>>> should do nothing if req->part is not set.
>>>
>>> The back trace of this bug is:
>>>
>>> BUG: kernel NULL pointer dereference, address: 000002ac
>>> #PF: supervisor write access in kernel mode
>>> #PF: error_code(0x0002) - not-present page
>>> *pde = 00000000
>>> Oops: 0002 [#1]
>>> CPU: 0 PID: 237 Comm: kworker/0:1H Not tainted
>>> 5.4.0-rc2-00011-g48d9b0d43105e #1
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1
>>> 04/01/2014
>>> Workqueue: kblockd drive_rq_insert_work
>>> EIP: blk_account_io_completion+0x7a/0xf0
>>> Code: 89 54 24 08 31 d2 89 4c 24 04 31 c9 c7 04 24 02 00 00 00 c1 ee
>>> 09 e8 f5 21 a6 ff e8 70 5c a7 ff 8b 53 60 8d 04 bd 00 00 00 00 <01> b4
>>> 02 ac 02 00 00 8b 9a 88 02 00 00 85 db 74 11 85 d2 74 51 8b
>>> EAX: 00000000 EBX: f5b80000 ECX: 00000000 EDX: 00000000
>>> ESI: 00000000 EDI: 00000000 EBP: f3031e70 ESP: f3031e54
>>> DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 EFLAGS: 00010046
>>> CR0: 80050033 CR2: 000002ac CR3: 03c25000 CR4: 000406d0
>>> Call Trace:
>>> <IRQ>
>>> blk_update_request+0x85/0x420
>>> ide_end_rq+0x38/0xa0
>>> ide_complete_rq+0x3d/0x70
>>> cdrom_newpc_intr+0x258/0xba0
>>> ide_intr+0x135/0x250
>>> __handle_irq_event_percpu+0x3e/0x250
>>> handle_irq_event_percpu+0x1f/0x50
>>> handle_irq_event+0x32/0x60
>>> handle_level_irq+0x6c/0x110
>>> handle_irq+0x72/0xa0
>>> </IRQ>
>>> do_IRQ+0x45/0xad
>>> common_interrupt+0x115/0x11c
>>
>> Why not just:
>>
>> diff --git a/block/blk.h b/block/blk.h
>> index 6842f28c033e..d7407b5d0200 100644
>> --- a/block/blk.h
>> +++ b/block/blk.h
>> @@ -250,7 +250,7 @@ int blk_dev_init(void);
>> */
>> static inline bool blk_do_io_stat(struct request *rq)
>> {
>> - return rq->rq_disk && (rq->rq_flags & RQF_IO_STAT);
>> + return rq->part && rq->rq_disk && (rq->rq_flags & RQF_IO_STAT);
>> }
>
> Because blk_account_io_start() also checks blk_do_io_stat() and, in that
> case, rq->part will never be set (seeing that's the function that
> typically sets it); thus that solution would disable stats entirely.
Gotcha. I'm fine with the patch you posted in that case.
--
Jens Axboe
