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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Zhengyuan Liu <liuzhengyuan@kylinos.cn>,
        Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5.2 214/215] io_uring: fix counter inc/dec mismatch in async_list
Date:   Mon, 29 Jul 2019 21:23:30 +0200
Message-Id: <20190729190816.978581666@linuxfoundation.org>
In-Reply-To: <20190729190739.971253303@linuxfoundation.org>
References: <20190729190739.971253303@linuxfoundation.org>
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From: Zhengyuan Liu <liuzhengyuan@kylinos.cn>

commit f7b76ac9d17e16e44feebb6d2749fec92bfd6dd4 upstream.

We could queue a work for each req in defer and link list without
increasing async_list->cnt, so we shouldn't decrease it while exiting
from workqueue as well if we didn't process the req in async list.

Thanks to Jens Axboe <axboe@kernel.dk> for his guidance.

Fixes: 31b515106428 ("io_uring: allow workqueue item to handle multiple buffered requests")
Signed-off-by: Zhengyuan Liu <liuzhengyuan@kylinos.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>


---
 fs/io_uring.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -331,6 +331,9 @@ struct io_kiocb {
 #define REQ_F_SEQ_PREV		8	/* sequential with previous */
 #define REQ_F_IO_DRAIN		16	/* drain existing IO first */
 #define REQ_F_IO_DRAINED	32	/* drain done */
+#define REQ_F_LINK		64	/* linked sqes */
+#define REQ_F_LINK_DONE		128	/* linked sqes done */
+#define REQ_F_FAIL_LINK		256	/* fail rest of links */
 	u64			user_data;
 	u32			error;	/* iopoll result from callback */
 	u32			sequence;
@@ -1698,6 +1701,10 @@ restart:
 		/* async context always use a copy of the sqe */
 		kfree(sqe);
 
+		/* req from defer and link list needn't decrease async cnt */
+		if (req->flags & (REQ_F_IO_DRAINED | REQ_F_LINK_DONE))
+			goto out;
+
 		if (!async_list)
 			break;
 		if (!list_empty(&req_list)) {
@@ -1745,6 +1752,7 @@ restart:
 		}
 	}
 
+out:
 	if (cur_mm) {
 		set_fs(old_fs);
 		unuse_mm(cur_mm);