io_uring: cancel reqs shouldn't kill overflow list

stable inclusion
from stable-5.10.4
commit b2ec2b12a45009e1801ea7b60bc644628d4ddee2
bugzilla: 46903

--------------------------------

[ Upstream commit cda286f0 ]

io_uring_cancel_task_requests() doesn't imply that the ring is going
away, it may continue to work well after that. The problem is that it
sets ->cq_overflow_flushed effectively disabling the CQ overflow feature

Split setting cq_overflow_flushed from flush, and do the first one only
on exit. It's ok in terms of cancellations because there is a
io_uring->in_idle check in __io_cqring_fill_event().

It also fixes a race with setting ->cq_overflow_flushed in
io_uring_cancel_task_requests, whuch's is not atomic and a part of a
bitmask with other flags. Though, the only other flag that's not set
during init is drain_next, so it's not as bad for sane architectures.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Fixes: 0f212204 ("io_uring: don't rely on weak ->files references")
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

fs/io_uring.c

@@ -1641,10 +1641,6 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force,
 
 	spin_lock_irqsave(&ctx->completion_lock, flags);
 
-	/* if force is set, the ring is going away. always drop after that */
-	if (force)
-		ctx->cq_overflow_flushed = 1;
-
 	cqe = NULL;
 	list_for_each_entry_safe(req, tmp, &ctx->cq_overflow_list, compl.list) {
 		if (tsk && req->task != tsk)
@@ -8378,6 +8374,8 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 {
 	mutex_lock(&ctx->uring_lock);
 	percpu_ref_kill(&ctx->refs);
+	/* if force is set, the ring is going away. always drop after that */
+	ctx->cq_overflow_flushed = 1;
 	if (ctx->rings)
 		io_cqring_overflow_flush(ctx, true, NULL, NULL);
 	mutex_unlock(&ctx->uring_lock);