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Commit 708e9295 authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon
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dm: skip second flush on bio unsupported error 



When processing barriers, skip the second flush if processing the bio
failed with -EOPNOTSUPP.  This can happen with discard+barrier requests.
If the device doesn't support discard, there would be two useless
SYNCHRONIZE CACHE commands.  The first dm_flush cannot be so easily
optimized out, so we leave it there.

Previously, -EOPNOTSUPP could be received in dec_pending only with empty
barriers and we ignored that error, assuming the device not supporting
cache flushes has cache always consistent.  With the addition of discard
barriers, this -EOPNOTSUPP can also be generated by discards and we
must record it in md->barrier_error for process_barrier.

Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 87c961cb

drivers/md/dm.c

+13 −2
Original line number Diff line number Diff line
@@ -639,8 +639,14 @@ static void dec_pending(struct dm_io *io, int error) 
			 * There can be just one barrier request so we use

			 * a per-device variable for error reporting.

			 * Note that you can't touch the bio after end_io_acct

			 *

			 * We ignore -EOPNOTSUPP for empty flush reported by

			 * underlying devices. We assume that if the device

			 * doesn't support empty barriers, it doesn't need

			 * cache flushing commands.

			 */

			if (!md->barrier_error && io_error != -EOPNOTSUPP)

			if (!md->barrier_error &&

			    !(bio_empty_barrier(bio) && io_error == -EOPNOTSUPP))

				md->barrier_error = io_error;

			end_io_acct(io);

			free_io(md, io);
@@ -2284,6 +2290,11 @@ static void process_barrier(struct mapped_device *md, struct bio *bio) 


	if (!bio_empty_barrier(bio)) {

		__split_and_process_bio(md, bio);

		/*

		 * If the request isn't supported, don't waste time with

		 * the second flush.

		 */

		if (md->barrier_error != -EOPNOTSUPP)

			dm_flush(md);

	}