On 03/12/2020 00:55, Ming Lei wrote:
Hi Ming,
Yeah, so I said that was another problem which you mentioned there, which
I'm not addressing, but I don't think that I'm making thing worse here.
The thing is that this patch does not fix the issue completely.
So AFAICS, the blk-mq/sched code doesn't wait for any "readers" to be
finished, such as those running blk_mq_queue_tag_busy_iter or
blk_mq_tagset_busy_iter() in another context.
So how about the idea of introducing some synchronization primitive, such as
semaphore, which those "readers" must grab and release at start and end (of
iter), to ensure the requests are not freed during the iteration?
It looks good, however devil is in details, please make into patch for
review.
OK, but another thing to say is that I need to find a somewhat reliable
reproducer for the potential problem you mention. So far this patch
solves the issue I see (in that kasan stops warning). Let me analyze
this a bit further.
Thanks,
John
