[PATCH] md/raid1: avoid reusing a resync bio after error handling.

[NeilBrown <neilb@suse.com>]

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fix_sync_read_error() modifies a bio on a newly faulty
device by setting bi_end_io to end_sync_write.
This ensure that put_buf() will still call rdev_dec_pending()
as required, but makes sure that subsequent code in
fix_sync_read_error() doesn't try to read from the device.

Unfortunately this interacts badly with sync_request_write()
which assumes that any bio with bi_end_io set to non-NULL
other than end_sync_read is safe to write to.

As the device is now faulty it doesn't make sense to write.
As the bio was recently used for a read, it is "dirty"
and not suitable for immediate submission.
In particular, ->bi_next might be non-NULL, which will cause
generic_make_request() to complain.

Break this interaction by refusing to write to devices
which are marked as Faulty.

Reported-and-tested-by: Michael Wang <yun.wang@profitbricks.com>
Fixes: 2e52d449bcec ("md/raid1: add failfast handling for reads.")
Cc: stable@vger.kernel.org (v4.10+)
Signed-off-by: NeilBrown <neilb@suse.com>
---
 drivers/md/raid1.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index a70283753a35..9c1b2231d2db 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2185,6 +2185,8 @@ static void sync_request_write(struct mddev *mddev, struct r1bio *r1_bio)
 		     (i == r1_bio->read_disk ||
 		      !test_bit(MD_RECOVERY_SYNC, &mddev->recovery))))
 			continue;
+		if (test_bit(Faulty, &conf->mirrors[i].rdev->flags))
+			continue;
 
 		bio_set_op_attrs(wbio, REQ_OP_WRITE, 0);
 		if (test_bit(FailFast, &conf->mirrors[i].rdev->flags))
-- 
2.12.2


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