From bd99c71bd14072ce2920f6d0c2fe43df072c653c Mon Sep 17 00:00:00 2001
From: Hao Xu <haoxu@linux.alibaba.com>
Date: Wed, 22 Sep 2021 18:12:36 +0800
Subject: [PATCH] io_uring: fix race between poll completion and cancel_hash
 insertion
Git-commit: bd99c71bd14072ce2920f6d0c2fe43df072c653c
Patch-mainline: v5.15-rc3
References: bsc#1199011

If poll arming and poll completion runs in parallel, there maybe races.
For instance, run io_poll_add in iowq and io_poll_task_func in original
context, then:

  iowq                                      original context
  io_poll_add
    vfs_poll
     (interruption happens
      tw queued to original
      context)                              io_poll_task_func
                                              generate cqe
                                              del from cancel_hash[]
    if !poll.done
      insert to cancel_hash[]

The entry left in cancel_hash[], similar case for fast poll.
Fix it by set poll.done = true when del from cancel_hash[].

Fixes: 5082620fb2ca ("io_uring: terminate multishot poll for CQ ring overflow")
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Link: https://lore.kernel.org/r/20210922101238.7177-2-haoxu@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Takashi Iwai <tiwai@suse.de>
[ddiss: revert from stable-5.14.9 to mainline fix]
Acked-by: David Disseldorp <ddiss@suse.de>

---
 fs/io_uring.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e372d5b9f6dc..43530aae6180 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5337,10 +5337,8 @@ static bool __io_poll_complete(struct io_kiocb *req, __poll_t mask)
 	}
 	if (req->poll.events & EPOLLONESHOT)
 		flags = 0;
-	if (!io_cqring_fill_event(ctx, req->user_data, error, flags)) {
-		req->poll.done = true;
+	if (!io_cqring_fill_event(ctx, req->user_data, error, flags))
 		flags = 0;
-	}
 	if (flags & IORING_CQE_F_MORE)
 		ctx->cq_extra++;
 
@@ -5371,6 +5369,7 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 		if (done) {
 			io_poll_remove_double(req);
 			hash_del(&req->hash_node);
+			req->poll.done = true;
 		} else {
 			req->result = 0;
 			add_wait_queue(req->poll.head, &req->poll.wait);
@@ -5508,6 +5507,7 @@ static void io_async_task_func(struct io_kiocb *req, bool *locked)
 
 	hash_del(&req->hash_node);
 	io_poll_remove_double(req);
+	apoll->poll.done = true;
 	spin_unlock(&ctx->completion_lock);
 
 	if (!READ_ONCE(apoll->poll.canceled))
-- 
2.34.1