From: Xiaoguang Wang xiaoguang.wang@linux.alibaba.com
[ Upstream commit bdcd3eab2a9ae0ac93f27275b6895dd95e5bf360 ]
After making ext4 support iopoll method: let ext4_file_operations's iopoll method be iomap_dio_iopoll(), we found fio can easily hang in fio_ioring_getevents() with below fio job: rm -f testfile; sync; sudo fio -name=fiotest -filename=testfile -iodepth=128 -thread -rw=write -ioengine=io_uring -hipri=1 -sqthread_poll=1 -direct=1 -bs=4k -size=10G -numjobs=8 -runtime=2000 -group_reporting with IORING_SETUP_SQPOLL and IORING_SETUP_IOPOLL enabled.
There are two issues that results in this hang, one reason is that when IORING_SETUP_SQPOLL and IORING_SETUP_IOPOLL are enabled, fio does not use io_uring_enter to get completed events, it relies on kernel io_sq_thread to poll for completed events.
Another reason is that there is a race: when io_submit_sqes() in io_sq_thread() submits a batch of sqes, variable 'inflight' will record the number of submitted reqs, then io_sq_thread will poll for reqs which have been added to poll_list. But note, if some previous reqs have been punted to io worker, these reqs will won't be in poll_list timely. io_sq_thread() will only poll for a part of previous submitted reqs, and then find poll_list is empty, reset variable 'inflight' to be zero. If app just waits these deferred reqs and does not wake up io_sq_thread again, then hang happens.
For app that entirely relies on io_sq_thread to poll completed requests, let io_iopoll_req_issued() wake up io_sq_thread properly when adding new element to poll_list, and when io_sq_thread prepares to sleep, check whether poll_list is empty again, if not empty, continue to poll.
Signed-off-by: Xiaoguang Wang xiaoguang.wang@linux.alibaba.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- fs/io_uring.c | 59 +++++++++++++++++++++++---------------------------- 1 file changed, 27 insertions(+), 32 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c index 60a4832089982..c8f8cc2463986 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1435,6 +1435,10 @@ static void io_iopoll_req_issued(struct io_kiocb *req) list_add(&req->list, &ctx->poll_list); else list_add_tail(&req->list, &ctx->poll_list); + + if ((ctx->flags & IORING_SETUP_SQPOLL) && + wq_has_sleeper(&ctx->sqo_wait)) + wake_up(&ctx->sqo_wait); }
static void io_file_put(struct io_submit_state *state) @@ -3857,9 +3861,8 @@ static int io_sq_thread(void *data) const struct cred *old_cred; mm_segment_t old_fs; DEFINE_WAIT(wait); - unsigned inflight; unsigned long timeout; - int ret; + int ret = 0;
complete(&ctx->completions[1]);
@@ -3867,39 +3870,19 @@ static int io_sq_thread(void *data) set_fs(USER_DS); old_cred = override_creds(ctx->creds);
- ret = timeout = inflight = 0; + timeout = jiffies + ctx->sq_thread_idle; while (!kthread_should_park()) { unsigned int to_submit;
- if (inflight) { + if (!list_empty(&ctx->poll_list)) { unsigned nr_events = 0;
- if (ctx->flags & IORING_SETUP_IOPOLL) { - /* - * inflight is the count of the maximum possible - * entries we submitted, but it can be smaller - * if we dropped some of them. If we don't have - * poll entries available, then we know that we - * have nothing left to poll for. Reset the - * inflight count to zero in that case. - */ - mutex_lock(&ctx->uring_lock); - if (!list_empty(&ctx->poll_list)) - io_iopoll_getevents(ctx, &nr_events, 0); - else - inflight = 0; - mutex_unlock(&ctx->uring_lock); - } else { - /* - * Normal IO, just pretend everything completed. - * We don't have to poll completions for that. - */ - nr_events = inflight; - } - - inflight -= nr_events; - if (!inflight) + mutex_lock(&ctx->uring_lock); + if (!list_empty(&ctx->poll_list)) + io_iopoll_getevents(ctx, &nr_events, 0); + else timeout = jiffies + ctx->sq_thread_idle; + mutex_unlock(&ctx->uring_lock); }
to_submit = io_sqring_entries(ctx); @@ -3928,7 +3911,7 @@ static int io_sq_thread(void *data) * more IO, we should wait for the application to * reap events and wake us up. */ - if (inflight || + if (!list_empty(&ctx->poll_list) || (!time_after(jiffies, timeout) && ret != -EBUSY && !percpu_ref_is_dying(&ctx->refs))) { cond_resched(); @@ -3938,6 +3921,19 @@ static int io_sq_thread(void *data) prepare_to_wait(&ctx->sqo_wait, &wait, TASK_INTERRUPTIBLE);
+ /* + * While doing polled IO, before going to sleep, we need + * to check if there are new reqs added to poll_list, it + * is because reqs may have been punted to io worker and + * will be added to poll_list later, hence check the + * poll_list again. + */ + if ((ctx->flags & IORING_SETUP_IOPOLL) && + !list_empty_careful(&ctx->poll_list)) { + finish_wait(&ctx->sqo_wait, &wait); + continue; + } + /* Tell userspace we may need a wakeup call */ ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP; /* make sure to read SQ tail after writing flags */ @@ -3966,8 +3962,7 @@ static int io_sq_thread(void *data) mutex_lock(&ctx->uring_lock); ret = io_submit_sqes(ctx, to_submit, NULL, -1, &cur_mm, true); mutex_unlock(&ctx->uring_lock); - if (ret > 0) - inflight += ret; + timeout = jiffies + ctx->sq_thread_idle; }
set_fs(old_fs);