[PATCH 5.10 141/171] io_uring: fix race between timeout flush and removal

[Greg Kroah-Hartman]

From: Jens Axboe <axboe@xxxxxxxxx>

commit e677edbcabee849bfdd43f1602bccbecf736a646 upstream.

io_flush_timeouts() assumes the timeout isn't in progress of triggering
or being removed/canceled, so it unconditionally removes it from the
timeout list and attempts to cancel it.

Leave it on the list and let the normal timeout cancelation take care
of it.

Cc: stable@xxxxxxxxxxxxxxx # 5.5+
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/io_uring.c |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1556,6 +1556,7 @@ static void __io_queue_deferred(struct i
 
 static void io_flush_timeouts(struct io_ring_ctx *ctx)
 {
+	struct io_kiocb *req, *tmp;
 	u32 seq;
 
 	if (list_empty(&ctx->timeout_list))
@@ -1563,10 +1564,8 @@ static void io_flush_timeouts(struct io_
 
 	seq = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
 
-	do {
+	list_for_each_entry_safe(req, tmp, &ctx->timeout_list, timeout.list) {
 		u32 events_needed, events_got;
-		struct io_kiocb *req = list_first_entry(&ctx->timeout_list,
-						struct io_kiocb, timeout.list);
 
 		if (io_is_timeout_noseq(req))
 			break;
@@ -1583,9 +1582,8 @@ static void io_flush_timeouts(struct io_
 		if (events_got < events_needed)
 			break;
 
-		list_del_init(&req->timeout.list);
 		io_kill_timeout(req, 0);
-	} while (!list_empty(&ctx->timeout_list));
+	}
 
 	ctx->cq_last_tm_flush = seq;
 }
@@ -5639,6 +5637,7 @@ static int io_timeout_prep(struct io_kio
 	else
 		data->mode = HRTIMER_MODE_REL;
 
+	INIT_LIST_HEAD(&req->timeout.list);
 	hrtimer_init(&data->timer, CLOCK_MONOTONIC, data->mode);
 	return 0;
 }
@@ -6282,12 +6281,12 @@ static enum hrtimer_restart io_link_time
 	if (!list_empty(&req->link_list)) {
 		prev = list_entry(req->link_list.prev, struct io_kiocb,
 				  link_list);
-		if (refcount_inc_not_zero(&prev->refs))
-			list_del_init(&req->link_list);
-		else
+		list_del_init(&req->link_list);
+		if (!refcount_inc_not_zero(&prev->refs))
 			prev = NULL;
 	}
 
+	list_del(&req->timeout.list);
 	spin_unlock_irqrestore(&ctx->completion_lock, flags);
 
 	if (prev) {