On 1/16/2020 1:26 PM, Jens Axboe wrote:
On 1/16/20 2:04 PM, Bijan Mottahedeh wrote:
On 1/16/2020 12:02 PM, Jens Axboe wrote:
On 1/16/20 12:08 PM, Bijan Mottahedeh wrote:
On 1/16/2020 8:22 AM, Jens Axboe wrote:
On 1/15/20 9:42 PM, Jens Axboe wrote:
On 1/15/20 9:34 PM, Jens Axboe wrote:
On 1/15/20 7:37 PM, Bijan Mottahedeh wrote:
io_issue_sqe() calls io_iopoll_req_issued() which manipulates poll_list,
so acquire ctx->uring_lock beforehand similar to other instances of
calling io_issue_sqe().
Is the below not enough?
This should be better, we have two that set ->in_async, and only one
doesn't hold the mutex.
If this works for you, can you resend patch 2 with that? Also add a:
Fixes: 8a4955ff1cca ("io_uring: sqthread should grab ctx->uring_lock for submissions")
to it as well. Thanks!
I tested and queued this up:
https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-5.5&id=11ba820bf163e224bf5dd44e545a66a44a5b1d7a
Please let me know if this works, it sits on top of the ->result patch you
sent in.
That works, thanks.
I'm however still seeing a use-after-free error in the request
completion path in nvme_unmap_data(). It happens only when testing with
large block sizes in fio, typically > 128k, e.g. bs=256k will always hit it.
This is the error:
DMA-API: nvme 0000:00:04.0: device driver tries to free DMA memory it
has not allocated [device address=0x6b6b6b6b6b6b6b6b] [size=1802201963
bytes]
and this warning occasionally:
WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE);
It seems like a request might be issued multiple times but I can't see
anything in io_uring code that would account for it.
Both of them indicate reuse, and I agree I don't think it's io_uring. It
really feels like an issue with nvme when a poll queue is shared, but I
haven't been able to pin point what it is yet.
The 128K is interesting, that would seem to indicate that it's related to
splitting of the IO (which would create > 1 IO per submitted IO).
Where does the split take place? I had suspected that it might be
related to the submit_bio() loop in __blkdev_direct_IO() but I don't
think I saw multiple submit_bio() calls or maybe I missed something.
See the path from blk_mq_make_request() -> __blk_queue_split() ->
blk_bio_segment_split(). The bio is built and submitted, then split if
it violates any size constraints. The splits are submitted through
generic_make_request(), so that might be why you didn't see multiple
submit_bio() calls.
I think the problem is in __blkdev_direct_IO() and not related to
request size:
qc = submit_bio(bio);
if (polled)
WRITE_ONCE(iocb->ki_cookie, qc);
The first call to submit_bio() when dio->is_sync is not set won't have
acquired a bio ref through bio_get() and so the bio/dio could be freed
when ki_cookie is set.
With the specific io_uring test, this happens because
blk_mq_make_request()->blk_mq_get_request() fails and so terminates the
request.
As for the fix for polled io (!is_sync) case, I'm wondering if
dio->multi_bio is really necessary in __blkdev_direct_IO(). Can we call
bio_get() unconditionally after the call to bio_alloc_bioset(), set
dio->ref = 1, and increment it for additional submit bio calls? Would
it make sense to do away with multi_bio?
Also, I'm not clear on how is_sync + mult_bio case is supposed to work.
__blkdev_direct_IO() polls for *a* completion in the request's hctx and
not *the* request completion itself, so what does that tell us for
multi_bio + is_sync? Is the polling supposed to guarantee that all
constituent bios for a mult_bio request have completed before return?
--bijan
PS I couldn't see 256k requests being split via __blk_queue_split(),
still not sure how that works.
