On 1/17/24 1:22 PM, Bart Van Assche wrote: > On 1/17/24 12:17, Jens Axboe wrote: >> On 1/17/24 1:16 PM, Gabriel Ryan wrote: >>> We found a race in the block message queue for kernel v5.18-rc5 using >>> a race testing tool we are developing. We are reporting this race >>> because it appears to be potentially harmful. The race occurs in >>> >>> block/blk-mq-sched.c:333 blk_mq_sched_dispatch_requests >>> >>> hctx->run++; >>> >>> where multiple threads can schedule dispatch requests and increment >>> the request counter htctx->run simultaneously. This appears to lead to >>> undefined behavior where multiple conflicting updates to the hctx->run >>> value could result in it not matching the number of requests that >>> have been scheduled with calls to blk_mq_sched_dispatch_requests. >> >> I suggest you take a closer look at how that variable is actually >> used. > > It's probably a good idea to explain this in a comment above the > code that increments hctx->runs because others may also be wondering > what the impact is of concurrent hctx->runs increments. If you do a quick grep, you'll very quickly see that it's just used for debugfs output. Being racy is not a problem. It should just get removed, honestly, like I did with some of the other accounting some time ago. -- Jens Axboe
