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Message-ID: <8bf6d549-cf66-4412-bebd-fd6e98166552@gmail.com>
Date: Mon, 18 Mar 2024 14:32:16 +0000
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Subject: Re: [PATCH v2 05/14] ublk: don't hard code IO_URING_F_UNLOCKED
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From: Pavel Begunkov <asml.silence@gmail.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: io-uring@vger.kernel.org, linux-block@vger.kernel.org,
Jens Axboe <axboe@kernel.dk>, Kanchan Joshi <joshi.k@samsung.com>
References: <cover.1710720150.git.asml.silence@gmail.com>
<a3928d3de14d2569efc2edd7fb654a4795ae7f86.1710720150.git.asml.silence@gmail.com>
<Zff4ShMEcL1WKZ1Q@fedora> <61b29658-e6a9-449f-a850-1881af1ecbee@gmail.com>
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On 3/18/24 13:37, Pavel Begunkov wrote:
> On 3/18/24 12:52, Pavel Begunkov wrote:
>> On 3/18/24 08:16, Ming Lei wrote:
>>> On Mon, Mar 18, 2024 at 12:41:50AM +0000, Pavel Begunkov wrote:
>>>> uring_cmd implementations should not try to guess issue_flags, just use
>>>> a newly added io_uring_cmd_complete(). We're loosing an optimisation in
>>>> the cancellation path in ublk_uring_cmd_cancel_fn(), but the assumption
>>>> is that we don't care that much about it.
>>>>
>>>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>>>> Link: https://lore.kernel.org/r/2f7bc9fbc98b11412d10b8fd88e58e35614e3147.1710514702.git.asml.silence@gmail.com
>>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>>> ---
>>>> drivers/block/ublk_drv.c | 18 ++++++++----------
>>>> 1 file changed, 8 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
>>>> index bea3d5cf8a83..97dceecadab2 100644
>>>> --- a/drivers/block/ublk_drv.c
>>>> +++ b/drivers/block/ublk_drv.c
>>>> @@ -1417,8 +1417,7 @@ static bool ublk_abort_requests(struct ublk_device *ub, struct ublk_queue *ubq)
>>>> return true;
>>>> }
>>>> -static void ublk_cancel_cmd(struct ublk_queue *ubq, struct ublk_io *io,
>>>> - unsigned int issue_flags)
>>>> +static void ublk_cancel_cmd(struct ublk_queue *ubq, struct ublk_io *io)
>>>> {
>>>> bool done;
>>>> @@ -1432,15 +1431,14 @@ static void ublk_cancel_cmd(struct ublk_queue *ubq, struct ublk_io *io,
>>>> spin_unlock(&ubq->cancel_lock);
>>>> if (!done)
>>>> - io_uring_cmd_done(io->cmd, UBLK_IO_RES_ABORT, 0, issue_flags);
>>>> + io_uring_cmd_complete(io->cmd, UBLK_IO_RES_ABORT, 0);
>>>> }
>>>> /*
>>>> * The ublk char device won't be closed when calling cancel fn, so both
>>>> * ublk device and queue are guaranteed to be live
>>>> */
>>>> -static void ublk_uring_cmd_cancel_fn(struct io_uring_cmd *cmd,
>>>> - unsigned int issue_flags)
>>>> +static void ublk_uring_cmd_cancel_fn(struct io_uring_cmd *cmd)
>>>> {
>>>> struct ublk_uring_cmd_pdu *pdu = ublk_get_uring_cmd_pdu(cmd);
>>>> struct ublk_queue *ubq = pdu->ubq;
>>>> @@ -1464,7 +1462,7 @@ static void ublk_uring_cmd_cancel_fn(struct io_uring_cmd *cmd,
>>>> io = &ubq->ios[pdu->tag];
>>>> WARN_ON_ONCE(io->cmd != cmd);
>>>> - ublk_cancel_cmd(ubq, io, issue_flags);
>>>> + ublk_cancel_cmd(ubq, io);
>>>
>>> .cancel_fn is always called with .uring_lock held, so this 'issue_flags' can't
>>> be removed, otherwise double task run is caused because .cancel_fn
>>> can be called multiple times if the request stays in ctx->cancelable_uring_cmd.
>>
>> I see, that's exactly why I was asking whether it can be deferred
>> to tw. Let me see if I can get by without that patch, but honestly
>> it's a horrible abuse of the ring state. Any ideas how that can be
>> cleaned up?
>
> I assume io_uring_try_cancel_uring_cmd() can run in parallel with
> completions, so there can be two parallel calls calls to ->uring_cmd
> (e.g. io-wq + cancel), which gives me shivers. Also, I'd rather
> no cancel in place requests of another task, io_submit_flush_completions()
> but it complicates things.
I'm wrong though on flush_completions, the task there cancels only
its own requests
io_uring_try_cancel_uring_cmd() {
...
if (!cancel_all && req->task != task)
continue;
}
> Is there any argument against removing requests from the cancellation
> list in io_uring_try_cancel_uring_cmd() before calling ->uring_cmd?
>
> io_uring_try_cancel_uring_cmd() {
> lock();
> for_each_req() {
> remove_req_from_cancel_list(req);
> req->file->uring_cmd();
> }
> unlock();
> }
>
--
Pavel Begunkov