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Date: Mon, 18 Mar 2024 12:52:33 +0000
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Subject: Re: [PATCH v2 05/14] ublk: don't hard code IO_URING_F_UNLOCKED
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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>
From: Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <Zff4ShMEcL1WKZ1Q@fedora>
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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?
--
Pavel Begunkov