Re: Re: [PATCH 2/2] block: Fix a race condition in submit_bio()

[syzbot <syzbot+ff9ab4a23afa7553@syzkaller.appspotmail.com>]

> On Tue, Jul 30, 2019 at 11:17:57AM -0700, Bart Van Assche wrote:
>> generic_make_request_checks() needs to be protected by a
>> blk_queue_enter() / blk_queue_exit() pair because it calls
>> blkcg_bio_issue_check() and because that last function calls
>> blkg_lookup().

>> This patch fixes  
>> https://syzkaller.appspot.com/bug?id=ff9ab4a23afa7553fb79f745a92be87ba4144508.

>> This patch also fixes the following kernel warning, triggered by
>> blktests:

>> WARNING: CPU: 5 PID: 10706 at block/blk-core.c:903  
>> generic_make_request_checks+0x9c6/0xe60
>> RIP: 0010:generic_make_request_checks+0x9c6/0xe60
>> Call Trace:
>>   generic_make_request+0x7a/0x5c0
>>   submit_bio+0x92/0x280
>>   mpage_readpages+0x2b1/0x300
>>   blkdev_readpages+0x1d/0x20
>>   read_pages+0xd9/0x2c0
>>   __do_page_cache_readahead+0x2e0/0x310
>>   force_page_cache_readahead+0xfb/0x170
>>   page_cache_sync_readahead+0x28d/0x2a0
>>   generic_file_read_iter+0xc13/0x1530
>>   blkdev_read_iter+0x7d/0x90
>>   new_sync_read+0x2c5/0x3d0
>>   __vfs_read+0x7b/0x90
>>   vfs_read+0xc6/0x1f0
>>   ksys_read+0xc3/0x160
>>   __x64_sys_read+0x43/0x50
>>   do_syscall_64+0x71/0x270
>>   entry_SYSCALL_64_after_hwframe+0x49/0xbe

>> Cc: Tejun Heo <tj@kernel.org>
>> Cc: Christoph Hellwig <hch@lst.de>
>> Cc: Ming Lei <ming.lei@redhat.com>
>> Cc: Hannes Reinecke <hare@suse.com>
>> Cc: Johannes Thumshirn <jthumshirn@suse.de>
>> Cc: Alexandru Moise <00moses.alexander00@gmail.com>
>> Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
>> Reported-by: syzbot+ff9ab4a23afa7553@syzkaller.appspotmail.com
>> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
>> ---
>>   block/blk-core.c | 13 ++++++++++++-
>>   1 file changed, 12 insertions(+), 1 deletion(-)

>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index ff27c3080348..cd844c54e9f1 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -1150,6 +1150,9 @@ EXPORT_SYMBOL_GPL(direct_make_request);
>>    */
>>   blk_qc_t submit_bio(struct bio *bio)
>>   {
>> +	struct request_queue *q = bio->bi_disk->queue;
>> +	blk_qc_t ret;
>> +
>>   	if (blkcg_punt_bio_submit(bio))
>>   		return BLK_QC_T_NONE;

>> @@ -1182,7 +1185,15 @@ blk_qc_t submit_bio(struct bio *bio)
>>   		}
>>   	}

>> -	return generic_make_request(bio);
>> +	if (unlikely(blk_queue_enter(q, 0) < 0)) {
>> +		bio->bi_status = BLK_STS_IOERR;
>> +		bio->bi_end_io(bio);
>> +		return BLK_QC_T_NONE;
>> +	}
>> +	ret = generic_make_request(bio);
>> +	blk_queue_exit(q);

> No, nested blk_queue_enter() is easy to cause deadlock.

> Thanks,
> Ming

I see the command but can't find the corresponding bug.
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