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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, Xiao Ni <xni@redhat.com>,
        Neil Brown <neilb@suse.com>, Shaohua Li <shli@fb.com>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.18 047/168] RAID10 BUG_ON in raise_barrier when force is true and conf->barrier is 0
Date:   Mon,  8 Oct 2018 20:30:27 +0200
Message-Id: <20181008175621.848482192@linuxfoundation.org>
In-Reply-To: <20181008175620.043587728@linuxfoundation.org>
References: <20181008175620.043587728@linuxfoundation.org>
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4.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Xiao Ni <xni@redhat.com>

[ Upstream commit 1d0ffd264204eba1861865560f1f7f7a92919384 ]

In raid10 reshape_request it gets max_sectors in read_balance. If the underlayer disks
have bad blocks, the max_sectors is less than last. It will call goto read_more many
times. It calls raise_barrier(conf, sectors_done != 0) every time. In this condition
sectors_done is not 0. So the value passed to the argument force of raise_barrier is
true.

In raise_barrier it checks conf->barrier when force is true. If force is true and
conf->barrier is 0, it panic. In this case reshape_request submits bio to under layer
disks. And in the callback function of the bio it calls lower_barrier. If the bio
finishes before calling raise_barrier again, it can trigger the BUG_ON.

Add one pair of raise_barrier/lower_barrier to fix this bug.

Signed-off-by: Xiao Ni <xni@redhat.com>
Suggested-by: Neil Brown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/md/raid10.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -4531,11 +4531,12 @@ static sector_t reshape_request(struct m
 		allow_barrier(conf);
 	}
 
+	raise_barrier(conf, 0);
 read_more:
 	/* Now schedule reads for blocks from sector_nr to last */
 	r10_bio = raid10_alloc_init_r10buf(conf);
 	r10_bio->state = 0;
-	raise_barrier(conf, sectors_done != 0);
+	raise_barrier(conf, 1);
 	atomic_set(&r10_bio->remaining, 0);
 	r10_bio->mddev = mddev;
 	r10_bio->sector = sector_nr;
@@ -4631,6 +4632,8 @@ read_more:
 	if (sector_nr <= last)
 		goto read_more;
 
+	lower_barrier(conf);
+
 	/* Now that we have done the whole section we can
 	 * update reshape_progress
 	 */