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Date: Mon, 18 Mar 2024 10:47:20 +0800
From: Ming Lei <ming.lei@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Pavel Begunkov <asml.silence@gmail.com>, io-uring@vger.kernel.org,
linux-block@vger.kernel.org, Kanchan Joshi <joshi.k@samsung.com>
Subject: Re: [PATCH v2 02/14] io_uring/cmd: fix tw <-> issue_flags conversion
Message-ID: <ZferOJCWcWoN2Qzf@fedora>
References: <cover.1710720150.git.asml.silence@gmail.com>
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In-Reply-To: <6291a6f9-61e0-4e3f-b070-b61e8764fb63@kernel.dk>
X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7
On Sun, Mar 17, 2024 at 08:40:59PM -0600, Jens Axboe wrote:
> On 3/17/24 8:32 PM, Pavel Begunkov wrote:
> > On 3/18/24 02:25, Jens Axboe wrote:
> >> On 3/17/24 8:23 PM, Ming Lei wrote:
> >>> On Mon, Mar 18, 2024 at 12:41:47AM +0000, Pavel Begunkov wrote:
> >>>> !IO_URING_F_UNLOCKED does not translate to availability of the deferred
> >>>> completion infra, IO_URING_F_COMPLETE_DEFER does, that what we should
> >>>> pass and look for to use io_req_complete_defer() and other variants.
> >>>>
> >>>> Luckily, it's not a real problem as two wrongs actually made it right,
> >>>> at least as far as io_uring_cmd_work() goes.
> >>>>
> >>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> >>>> Link: https://lore.kernel.org/r/eb08e72e837106963bc7bc7dccfd93d646cc7f36.1710514702.git.asml.silence@gmail.com
> >>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> >
> > oops, I should've removed all the signed-offs
> >
> >>>> ---
> >>>> io_uring/uring_cmd.c | 10 ++++++++--
> >>>> 1 file changed, 8 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> >>>> index f197e8c22965..ec38a8d4836d 100644
> >>>> --- a/io_uring/uring_cmd.c
> >>>> +++ b/io_uring/uring_cmd.c
> >>>> @@ -56,7 +56,11 @@ EXPORT_SYMBOL_GPL(io_uring_cmd_mark_cancelable);
> >>>> static void io_uring_cmd_work(struct io_kiocb *req, struct io_tw_state *ts)
> >>>> {
> >>>> struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
> >>>> - unsigned issue_flags = ts->locked ? 0 : IO_URING_F_UNLOCKED;
> >>>> + unsigned issue_flags = IO_URING_F_UNLOCKED;
> >>>> +
> >>>> + /* locked task_work executor checks the deffered list completion */
> >>>> + if (ts->locked)
> >>>> + issue_flags = IO_URING_F_COMPLETE_DEFER;
> >>>> ioucmd->task_work_cb(ioucmd, issue_flags);
> >>>> }
> >>>> @@ -100,7 +104,9 @@ void io_uring_cmd_done(struct io_uring_cmd *ioucmd, ssize_t ret, ssize_t res2,
> >>>> if (req->ctx->flags & IORING_SETUP_IOPOLL) {
> >>>> /* order with io_iopoll_req_issued() checking ->iopoll_complete */
> >>>> smp_store_release(&req->iopoll_completed, 1);
> >>>> - } else if (!(issue_flags & IO_URING_F_UNLOCKED)) {
> >>>> + } else if (issue_flags & IO_URING_F_COMPLETE_DEFER) {
> >>>> + if (WARN_ON_ONCE(issue_flags & IO_URING_F_UNLOCKED))
> >>>> + return;
> >>>> io_req_complete_defer(req);
> >>>> } else {
> >>>> req->io_task_work.func = io_req_task_complete;
> >>>
> >>> 'git-bisect' shows the reported warning starts from this patch.
> >
> > Thanks Ming
> >
> >>
> >> That does make sense, as probably:
> >>
> >> + /* locked task_work executor checks the deffered list completion */
> >> + if (ts->locked)
> >> + issue_flags = IO_URING_F_COMPLETE_DEFER;
> >>
> >> this assumption isn't true, and that would mess with the task management
> >> (which is in your oops).
> >
> > I'm missing it, how it's not true?
> >
> >
> > static void ctx_flush_and_put(struct io_ring_ctx *ctx, struct io_tw_state *ts)
> > {
> > ...
> > if (ts->locked) {
> > io_submit_flush_completions(ctx);
> > ...
> > }
> > }
> >
> > static __cold void io_fallback_req_func(struct work_struct *work)
> > {
> > ...
> > mutex_lock(&ctx->uring_lock);
> > llist_for_each_entry_safe(req, tmp, node, io_task_work.node)
> > req->io_task_work.func(req, &ts);
> > io_submit_flush_completions(ctx);
> > mutex_unlock(&ctx->uring_lock);
> > ...
> > }
>
> I took a look too, and don't immediately see it. Those are also the two
> only cases I found, and before the patches, looks fine too.
>
> So no immediate answer there... But I can confirm that before this
> patch, test passes fine. With the patch, it goes boom pretty quick.
> Either directly off putting the task, or an unrelated memory crash
> instead.
In ublk, the translated 'issue_flags' is passed to io_uring_cmd_done()
from ioucmd->task_work_cb()(__ublk_rq_task_work()). That might be
related with the reason.
Thanks,
Ming