On 6/21/20 11:50 PM, Xuan Zhuo wrote: > When the user consumes and generates sqe at a fast rate, > io_sqring_entries can always get sqe, and ret will not be equal to -EBUSY, > so that io_sq_thread will never call cond_resched or schedule, and then > we will get the following system error prompt: > > rcu: INFO: rcu_sched self-detected stall on CPU > or > watchdog: BUG: soft lockup-CPU#23 stuck for 112s! [io_uring-sq:1863] > > This patch adds a check after io_submit_sqes. If io_sq_thread does not call > cond_resched or schedule for more than HZ/2, it will call them. This looks reasonable. It'd be easier if we could just cond_resched() after the call unconditionally, but that would not drop the mm. But maybe we can just drop the timeout and just rely on need_resched() for this, ala the below? diff --git a/fs/io_uring.c b/fs/io_uring.c index c686061c3762..955d0765f302 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -6248,7 +6248,7 @@ static int io_sq_thread(void *data) * If submit got -EBUSY, flag us as needing the application * to enter the kernel to reap and flush events. */ - if (!to_submit || ret == -EBUSY) { + if (!to_submit || ret == -EBUSY || need_resched()) { /* * Drop cur_mm before scheduling, we can't hold it for * long periods (or over schedule()). Do this before @@ -6264,7 +6264,7 @@ static int io_sq_thread(void *data) * more IO, we should wait for the application to * reap events and wake us up. */ - if (!list_empty(&ctx->poll_list) || + if (!list_empty(&ctx->poll_list) || need_resched() || (!time_after(jiffies, timeout) && ret != -EBUSY && !percpu_ref_is_dying(&ctx->refs))) { if (current->task_works) -- Jens Axboe