This is a note to let you know that I've just added the patch titled
dm thin: do not send discards to shared blocks
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
dm-thin-do-not-send-discards-to-shared-blocks.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 650d2a06b4fe1cc1d218c20e256650f68bf0ca31 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <[email protected]>
Date: Fri, 20 Jul 2012 14:25:05 +0100
Subject: dm thin: do not send discards to shared blocks
From: Mikulas Patocka <[email protected]>
commit 650d2a06b4fe1cc1d218c20e256650f68bf0ca31 upstream.
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
104655fd4dcebd50068ef30253a001da72e3a081 (dm thin: support discards).
Signed-off-by: Mikulas Patocka <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>
Signed-off-by: Alasdair G Kergon <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/md/dm-thin.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1240,7 +1240,10 @@ static void process_discard(struct thin_
cell_release_singleton(cell, bio);
cell_release_singleton(cell2, bio);
- remap_and_issue(tc, bio, lookup_result.block);
+ if ((!lookup_result.shared) &&
pool->pf.discard_passdown)
+ remap_and_issue(tc, bio, lookup_result.block);
+ else
+ bio_endio(bio, 0);
}
break;
@@ -2575,6 +2578,7 @@ static int thin_ctr(struct dm_target *ti
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);
Patches currently in stable-queue which might be from [email protected] are
queue-3.4/dm-raid1-fix-crash-with-mirror-recovery-and-discard.patch
queue-3.4/dm-raid1-set-discard_zeroes_data_unsupported.patch
queue-3.4/dm-thin-do-not-send-discards-to-shared-blocks.patch
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