Re: [PATCH v2 05/14] ublk: don't hard code IO_URING_F_UNLOCKED

[Pavel Begunkov <asml.silence@gmail.com>]

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