io_uring/msg_ring: fix overflow posting

The caller of io_cqring_event_overflow() should be holding the
completion_lock, which is violated by io_msg_tw_complete. There
is only one caller of io_add_aux_cqe(), so just add locking there
for now.

WARNING: CPU: 0 PID: 5145 at io_uring/io_uring.c:703 io_cqring_event_overflow+0x442/0x660 io_uring/io_uring.c:703
RIP: 0010:io_cqring_event_overflow+0x442/0x660 io_uring/io_uring.c:703
 <TASK>
 __io_post_aux_cqe io_uring/io_uring.c:816 [inline]
 io_add_aux_cqe+0x27c/0x320 io_uring/io_uring.c:837
 io_msg_tw_complete+0x9d/0x4d0 io_uring/msg_ring.c:78
 io_fallback_req_func+0xce/0x1c0 io_uring/io_uring.c:256
 process_one_work kernel/workqueue.c:3224 [inline]
 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3305
 worker_thread+0x86d/0xd40 kernel/workqueue.c:3383
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:144
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Fixes: f33096a ("io_uring: add io_add_aux_cqe() helper")
Reported-by: [email protected]
Signed-off-by: Pavel Begunkov <[email protected]>
Link: https://lore.kernel.org/r/c7350d07fefe8cce32b50f57665edbb6355ea8c1.1719927398.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <[email protected]>

Author: isilence

io_uring/io_uring.c

@@ -834,7 +834,11 @@ bool io_post_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags
  */
 void io_add_aux_cqe(struct io_ring_ctx *ctx, u64 user_data, s32 res, u32 cflags)
 {
-	__io_post_aux_cqe(ctx, user_data, res, cflags);
+	if (!io_fill_cqe_aux(ctx, user_data, res, cflags)) {
+		spin_lock(&ctx->completion_lock);
+		io_cqring_event_overflow(ctx, user_data, res, cflags, 0, 0);
+		spin_unlock(&ctx->completion_lock);
+	}
 	ctx->submit_state.cq_flush = true;
 }