On 10/26/2016 04:51 PM, Linus Torvalds wrote:
On Wed, Oct 26, 2016 at 3:40 PM, Dave Jones <da...@codemonkey.org.uk> wrote:
I gave it a shot too for shits & giggles.
This falls out during boot.
[ 9.278420] WARNING: CPU: 0 PID: 1 at block/blk-mq.c:1181
blk_sq_make_request+0x465/0x4a0
Hmm. That's the
WARN_ON_ONCE(rq->mq_ctx != ctx);
that I added to blk_mq_merge_queue_io(), and I really think that
warning is valid, and the fact that it triggers shows that something
is wrong with locking.
We just did a
spin_lock(&ctx->lock);
and that lock is *supposed* to protect the __blk_mq_insert_request(),
but that uses rq->mq_ctx.
So if rq->mq_ctx != ctx, then we're locking the wrong context.
Jens - please explain to me why I'm wrong.
Or maybe I actually might have found the problem? In which case please
send me a patch that fixes it ;)
I think you're pretty close, the two should not be different and I don't
immediately see how. I'll run some testing here, should be easier with
this knowledge.
Dave: it might be a good idea to split that "WARN_ON_ONCE()" in
blk_mq_merge_queue_io() into two, since right now it can trigger both
for the
blk_mq_bio_to_request(rq, bio);
path _and_ for the
if (!blk_mq_attempt_merge(q, ctx, bio)) {
blk_mq_bio_to_request(rq, bio);
goto insert_rq;
And just in case I can't trigger, would be interesting to add a call to
blk_rq_dump_flags() as well, in case this is some special request.
--
Jens Axboe