[PATCH 5.10 3/5] io_uring: fix racy IOPOLL flush overflow

[Pavel Begunkov <asml.silence@gmail.com>]

It's not safe to call io_cqring_overflow_flush() for IOPOLL mode without
hodling uring_lock, because it does synchronisation differently. Make
sure we have it.

As for io_ring_exit_work(), we don't even need it there because
io_ring_ctx_wait_and_kill() already set force flag making all overflowed
requests to be dropped.

Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 4fac02ea5f4c..b1ba9a738315 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8393,8 +8393,6 @@ static void io_ring_exit_work(struct work_struct *work)
 	 * as nobody else will be looking for them.
 	 */
 	do {
-		if (ctx->rings)
-			io_cqring_overflow_flush(ctx, true, NULL, NULL);
 		io_iopoll_try_reap_events(ctx);
 	} while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
 	io_ring_ctx_free(ctx);
@@ -8404,6 +8402,8 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 {
 	mutex_lock(&ctx->uring_lock);
 	percpu_ref_kill(&ctx->refs);
+	if (ctx->rings)
+		io_cqring_overflow_flush(ctx, true, NULL, NULL);
 	mutex_unlock(&ctx->uring_lock);
 
 	io_kill_timeouts(ctx, NULL);
@@ -8413,8 +8413,6 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 		io_wq_cancel_all(ctx->io_wq);
 
 	/* if we failed setting up the ctx, we might not have any rings */
-	if (ctx->rings)
-		io_cqring_overflow_flush(ctx, true, NULL, NULL);
 	io_iopoll_try_reap_events(ctx);
 	idr_for_each(&ctx->personality_idr, io_remove_personalities, ctx);
 
@@ -8691,7 +8689,9 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
 	else
 		io_cancel_defer_files(ctx, task, NULL);
 
+	io_ring_submit_lock(ctx, (ctx->flags & IORING_SETUP_IOPOLL));
 	io_cqring_overflow_flush(ctx, true, task, files);
+	io_ring_submit_unlock(ctx, (ctx->flags & IORING_SETUP_IOPOLL));
 
 	while (__io_uring_cancel_task_requests(ctx, task, files)) {
 		io_run_task_work();
@@ -8993,8 +8993,10 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
 	 */
 	ret = 0;
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		io_ring_submit_lock(ctx, (ctx->flags & IORING_SETUP_IOPOLL));
 		if (!list_empty_careful(&ctx->cq_overflow_list))
 			io_cqring_overflow_flush(ctx, false, NULL, NULL);
+		io_ring_submit_unlock(ctx, (ctx->flags & IORING_SETUP_IOPOLL));
 		if (flags & IORING_ENTER_SQ_WAKEUP)
 			wake_up(&ctx->sq_data->wait);
 		if (flags & IORING_ENTER_SQ_WAIT)
-- 
2.24.0