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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,
        Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5.10 516/717] io_uring: fix io_wqe->work_list corruption
Date:   Mon, 28 Dec 2020 13:48:34 +0100
Message-Id: <20201228125045.676509466@linuxfoundation.org>
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From: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

commit 0020ef04e48571a88d4f482ad08f71052c5c5a08 upstream.

For the first time a req punted to io-wq, we'll initialize io_wq_work's
list to be NULL, then insert req to io_wqe->work_list. If this req is not
inserted into tail of io_wqe->work_list, this req's io_wq_work list will
point to another req's io_wq_work. For splitted bio case, this req maybe
inserted to io_wqe->work_list repeatedly, once we insert it to tail of
io_wqe->work_list for the second time, now io_wq_work->list->next will be
invalid pointer, which then result in many strang error, panic, kernel
soft-lockup, rcu stall, etc.

In my vm, kernel doest not have commit cc29e1bf0d63f7 ("block: disable
iopoll for split bio"), below fio job can reproduce this bug steadily:
[global]
name=iouring-sqpoll-iopoll-1
ioengine=io_uring
iodepth=128
numjobs=1
thread
rw=randread
direct=1
registerfiles=1
hipri=1
bs=4m
size=100M
runtime=120
time_based
group_reporting
randrepeat=0

[device]
directory=/home/feiman.wxg/mntpoint/  # an ext4 mount point

If we have commit cc29e1bf0d63f7 ("block: disable iopoll for split bio"),
there will no splitted bio case for polled io, but I think we still to need
to fix this list corruption, it also should maybe go to stable branchs.

To fix this corruption, if a req is inserted into tail of io_wqe->work_list,
initialize req->io_wq_work->list->next to bu NULL.

Cc: stable@vger.kernel.org
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/io-wq.h |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -59,6 +59,7 @@ static inline void wq_list_add_tail(stru
 		list->last->next = node;
 		list->last = node;
 	}
+	node->next = NULL;
 }
 
 static inline void wq_list_cut(struct io_wq_work_list *list,