Commit 650d2a06 authored Jul 20, 2012 by Mikulas Patocka Committed by Alasdair G Kergon Jul 20, 2012

dm thin: do not send discards to shared blocks



When process_discard receives a partial discard that doesn't cover a
full block, it sends this discard down to that block. Unfortunately, the
block can be shared and the discard would corrupt the other snapshots
sharing this block.

This patch detects block sharing and ends the discard with success when
sending it to the shared block.

The above change means that if the device supports discard it can't be
guaranteed that a discard request zeroes data. Therefore, we set
ti->discard_zeroes_data_unsupported.

Thin target discard support with this bug arrived in commit
104655fd (dm thin: support discards).

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

parent 751f188d

drivers/md/dm-thin.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -1245,7 +1245,10 @@ static void process_discard(struct thin_c tc, struct bio bio)

		cell_release_singleton(cell, bio);
		cell_release_singleton(cell2, bio);
		if ((!lookup_result.shared) && pool->pf.discard_passdown)
		remap_and_issue(tc, bio, lookup_result.block);
		else
		bio_endio(bio, 0);
		}
		break;

		@@ -2628,6 +2631,7 @@ static int thin_ctr(struct dm_target ti, unsigned argc, char *argv)
		if (tc->pool->pf.discard_enabled) {
		ti->discards_supported = 1;
		ti->num_discard_requests = 1;
		ti->discard_zeroes_data_unsupported = 1;
		}

		dm_put(pool_md);

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