6.12-stable review patch. If anyone has any objections, please let me know.
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From: Jens Axboe axboe@kernel.dk
Commit e15cb2200b934e507273510ba6bc747d5cde24a3 upstream.
Using min_wait, two timeouts are given:
1) The min_wait timeout, within which up to 'wait_nr' events are waited for. 2) The overall long timeout, which is entered if no events are generated in the min_wait window.
If the min_wait has expired, any event being posted must wake the task. For SQPOLL, that isn't the case, as it won't trigger the io_has_work() condition, as it will have already processed the task_work that happened when an event was posted. This causes any event to trigger post the min_wait to not always cause the waiting application to wakeup, and instead it will wait until the overall timeout has expired. This can be shown in a test case that has a 1 second min_wait, with a 5 second overall wait, even if an event triggers after 1.5 seconds:
axboe@m2max-kvm /d/iouring-mre (master)> zig-out/bin/iouring info: MIN_TIMEOUT supported: true, features: 0x3ffff info: Testing: min_wait=1000ms, timeout=5s, wait_nr=4 info: 1 cqes in 5000.2ms
where the expected result should be:
axboe@m2max-kvm /d/iouring-mre (master)> zig-out/bin/iouring info: MIN_TIMEOUT supported: true, features: 0x3ffff info: Testing: min_wait=1000ms, timeout=5s, wait_nr=4 info: 1 cqes in 1500.3ms
When the min_wait timeout triggers, reset the number of completions needed to wake the task. This should ensure that any future events will wake the task, regardless of how many events it originally wanted to wait for.
Reported-by: Tip ten Brink tip@tenbrinkmeijs.com Cc: stable@vger.kernel.org Fixes: 1100c4a2656d ("io_uring: add support for batch wait timeout") Link: https://github.com/axboe/liburing/issues/1477 Signed-off-by: Jens Axboe axboe@kernel.dk (cherry picked from commit e15cb2200b934e507273510ba6bc747d5cde24a3) Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/io_uring.c | 3 +++ 1 file changed, 3 insertions(+)
--- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -2421,6 +2421,9 @@ static enum hrtimer_restart io_cqring_mi goto out_wake; }
+ /* any generated CQE posted past this time should wake us up */ + iowq->cq_tail = iowq->cq_min_tail; + iowq->t.function = io_cqring_timer_wakeup; hrtimer_set_expires(timer, iowq->timeout); return HRTIMER_RESTART;