On 06/07/2020 17:31, Jens Axboe wrote:
> On 7/6/20 8:14 AM, Pavel Begunkov wrote:
>> It's not nice to hold @uring_lock for too long io_iopoll_reap_events().
>> For instance, the lock is needed to publish requests to @poll_list, and
>> that locks out tasks doing that for no good reason. Loose it
>> occasionally.
>>
>> Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
>> ---
>> fs/io_uring.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 020944a193d0..568e25bcadd6 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -2059,11 +2059,14 @@ static void io_iopoll_reap_events(struct io_ring_ctx *ctx)
>>
>> io_iopoll_getevents(ctx, &nr_events, 1);
>>
>> + /* task_work takes the lock to publish a req to @poll_list */
>> + mutex_unlock(&ctx->uring_lock);
>> /*
>> * Ensure we allow local-to-the-cpu processing to take place,
>> * in this case we need to ensure that we reap all events.
>> */
>> cond_resched();
>> + mutex_lock(&ctx->uring_lock);
>> }
>> mutex_unlock(&ctx->uring_lock);
>> }
>
> This would be much better written as:
>
> if (need_resched()) {
> mutex_unlock(&ctx->uring_lock);
> cond_resched();
> mutex_lock(&ctx->uring_lock);
> }
>
> to avoid shuffling the lock when not needed to. Every cycle counts for
> polled IO.
It happens only when io_uring is being killed, can't imagine any sane app
trying to catch CQEs after doing that. I'll resend
--
Pavel Begunkov
