[3.8.y.z extended stable] Patch "dm thin: switch to read-only mode if metadata space is exhausted" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    dm thin: switch to read-only mode if metadata space is exhausted

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 9553b382b4c3a0e0c0a01567f57f8317d763f95a Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer at redhat.com>
Date: Tue, 3 Dec 2013 12:20:57 -0500
Subject: dm thin: switch to read-only mode if metadata space is exhausted

commit 4a02b34e0cf1d0d0dd3737702841da4bf615a50a upstream.

Switch the thin pool to read-only mode in alloc_data_block() if
dm_pool_alloc_data_block() fails because the pool's metadata space is
exhausted.

Differentiate between data and metadata space in messages about no
free space available.

This issue was noticed with the device-mapper-test-suite using:
dmtest run --suite thin-provisioning -n /exhausting_metadata_space_causes_fail_mode/

The quantity of errors logged in this case must be reduced.

before patch:

device-mapper: thin: 253:4: reached low water mark for metadata device: sending event.
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: space map common: dm_tm_shadow_block() failed
<snip ... these repeat for a _very_ long while ... >
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: thin: 253:4: commit failed: error = -28
device-mapper: thin: 253:4: switching pool to read-only mode

after patch:

device-mapper: thin: 253:4: reached low water mark for metadata device: sending event.
device-mapper: space map metadata: unable to allocate new metadata block
device-mapper: thin: 253:4: no free metadata space available.
device-mapper: thin: 253:4: switching pool to read-only mode

Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Acked-by: Joe Thornber <ejt at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm-thin.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index a3d00dd..c29e967 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -878,7 +878,7 @@ static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
 			 * doing all this checking and return -ENOSPC.
 			 */
 			if (!free_blocks) {
-				DMWARN("%s: no free space available.",
+				DMWARN("%s: no free data space available.",
 				       dm_device_name(pool->pool_md));
 				spin_lock_irqsave(&pool->lock, flags);
 				pool->no_free_space = 1;
@@ -889,8 +889,16 @@ static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
 	}

 	r = dm_pool_alloc_data_block(pool->pmd, result);
-	if (r)
+	if (r) {
+		if (r == -ENOSPC &&
+		    !dm_pool_get_free_metadata_block_count(pool->pmd, &free_blocks) &&
+		    !free_blocks) {
+			DMWARN("%s: no free metadata space available.",
+			       dm_device_name(pool->pool_md));
+			set_pool_mode(pool, PM_READ_ONLY);
+		}
 		return r;
+	}

 	return 0;
 }
--
1.8.3.2