Re: [PATCH] blk-mq: Avoid that submitting a bio concurrently with device removal triggers a crash

[Jens Axboe <axboe@kernel.dk>]

On 4/10/18 8:05 PM, Ming Lei wrote:
> On Tue, Apr 10, 2018 at 02:30:35PM -0600, Bart Van Assche wrote:
>> Because blkcg_exit_queue() is now called from inside blk_cleanup_queue()
>> it is no longer safe to access cgroup information during or after the
>> blk_cleanup_queue() call. Hence protect the generic_make_request_checks()
>> call with blk_queue_enter() / blk_queue_exit().
>>
>> Reported-by: Ming Lei <ming.lei@redhat.com>
>> Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the block cgroup controller")
>> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
>> Cc: Ming Lei <ming.lei@redhat.com>
>> Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
>> ---
>>  block/blk-core.c | 32 ++++++++++++++++++++++++++------
>>  1 file changed, 26 insertions(+), 6 deletions(-)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 34e2f2227fd9..a330cd2829e1 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -2386,8 +2386,19 @@ blk_qc_t generic_make_request(struct bio *bio)
>>  	 * yet.
>>  	 */
>>  	struct bio_list bio_list_on_stack[2];
>> +	blk_mq_req_flags_t flags = bio->bi_opf & REQ_NOWAIT ?
>> +		BLK_MQ_REQ_NOWAIT : 0;
>> +	struct request_queue *q = bio->bi_disk->queue;
>>  	blk_qc_t ret = BLK_QC_T_NONE;
>>  
>> +	if (blk_queue_enter(q, flags) < 0) {
> 
> As I mentioned last time, the queue pointer has to be checked before
> calling blk_queue_enter(), since it isn't difficult to trigger the
> failure log of 'generic_make_request: Trying to access nonexistent
> block-device'.

That's a good point, the NULL check needs to be included first. Bart,
do you want to send an update? I can just rebase the for-linus branch.

-- 
Jens Axboe