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. Thanks, Bart.
