[PATCH AUTOSEL 5.7 39/53] io_uring: fix io_sq_thread no schedule when busy

[PATCH AUTOSEL 5.7 39/53] io_uring: fix io_sq_thread no schedule when busy

[Sasha Levin]

From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

[ Upstream commit b772f07add1c0b22e02c0f1e96f647560679d3a9 ]

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 checks whether need to call cond_resched() by checking
the need_resched() function every cycle.

Suggested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/io_uring.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1829be7f63a35..6cf9d509371e2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6071,7 +6071,7 @@ 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
@@ -6087,7 +6087,7 @@ 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)
-- 
2.25.1

[PATCH AUTOSEL 5.7 49/53] io_uring: fix current->mm NULL dereference on exit

[Sasha Levin]

From: Pavel Begunkov <asml.silence@gmail.com>

[ Upstream commit d60b5fbc1ce8210759b568da49d149b868e7c6d3 ]

Don't reissue requests from io_iopoll_reap_events(), the task may not
have mm, which ends up with NULL. It's better to kill everything off on
exit anyway.

[  677.734670] RIP: 0010:io_iopoll_complete+0x27e/0x630
...
[  677.734679] Call Trace:
[  677.734695]  ? __send_signal+0x1f2/0x420
[  677.734698]  ? _raw_spin_unlock_irqrestore+0x24/0x40
[  677.734699]  ? send_signal+0xf5/0x140
[  677.734700]  io_iopoll_getevents+0x12f/0x1a0
[  677.734702]  io_iopoll_reap_events.part.0+0x5e/0xa0
[  677.734703]  io_ring_ctx_wait_and_kill+0x132/0x1c0
[  677.734704]  io_uring_release+0x20/0x30
[  677.734706]  __fput+0xcd/0x230
[  677.734707]  ____fput+0xe/0x10
[  677.734709]  task_work_run+0x67/0xa0
[  677.734710]  do_exit+0x35d/0xb70
[  677.734712]  do_group_exit+0x43/0xa0
[  677.734713]  get_signal+0x140/0x900
[  677.734715]  do_signal+0x37/0x780
[  677.734717]  ? enqueue_hrtimer+0x41/0xb0
[  677.734718]  ? recalibrate_cpu_khz+0x10/0x10
[  677.734720]  ? ktime_get+0x3e/0xa0
[  677.734721]  ? lapic_next_deadline+0x26/0x30
[  677.734723]  ? tick_program_event+0x4d/0x90
[  677.734724]  ? __hrtimer_get_next_event+0x4d/0x80
[  677.734726]  __prepare_exit_to_usermode+0x126/0x1c0
[  677.734741]  prepare_exit_to_usermode+0x9/0x40
[  677.734742]  idtentry_exit_cond_rcu+0x4c/0x60
[  677.734743]  sysvec_reschedule_ipi+0x92/0x160
[  677.734744]  ? asm_sysvec_reschedule_ipi+0xa/0x20
[  677.734745]  asm_sysvec_reschedule_ipi+0x12/0x20

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/io_uring.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6cf9d509371e2..43dc745727408 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -858,6 +858,7 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 				 struct io_uring_files_update *ip,
 				 unsigned nr_args);
 static int io_grab_files(struct io_kiocb *req);
+static void io_complete_rw_common(struct kiocb *kiocb, long res);
 static void io_cleanup_req(struct io_kiocb *req);
 static int io_file_get(struct io_submit_state *state, struct io_kiocb *req,
 		       int fd, struct file **out_file, bool fixed);
@@ -1697,6 +1698,14 @@ static void io_iopoll_queue(struct list_head *again)
 	do {
 		req = list_first_entry(again, struct io_kiocb, list);
 		list_del(&req->list);
+
+		/* shouldn't happen unless io_uring is dying, cancel reqs */
+		if (unlikely(!current->mm)) {
+			io_complete_rw_common(&req->rw.kiocb, -EAGAIN);
+			io_put_req(req);
+			continue;
+		}
+
 		refcount_inc(&req->refs);
 		io_queue_async_work(req);
 	} while (!list_empty(again));
-- 
2.25.1