linux-ext4 - [PATCH v2.6.32.y 29/53] ext4: Issue the discard operation *before* releasing the blocks to be reused

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Date:	Sun, 30 May 2010 22:49:42 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	stable@...nel.org
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Theodore Ts'o <tytso@....edu>
Subject: [PATCH v2.6.32.y 29/53] ext4: Issue the discard operation *before* releasing the blocks to be reused

commit b90f687018e6d6c77d981b09203780f7001407e5 upstream (as of v2.6.34-rc6)

Otherwise, we can end up having data corruption because the blocks
could get reused and then discarded!

https://bugzilla.kernel.org/show_bug.cgi?id=15579

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 fs/ext4/mballoc.c |   24 +++++++++++-------------
 1 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 8216789..65c2b79 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2537,6 +2537,17 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 		mb_debug(1, "gonna free %u blocks in group %u (0x%p):",
 			 entry->count, entry->group, entry);
 
+		if (test_opt(sb, DISCARD)) {
+			ext4_fsblk_t discard_block;
+
+			discard_block = entry->start_blk +
+				ext4_group_first_block_no(sb, entry->group);
+			trace_ext4_discard_blocks(sb,
+					(unsigned long long)discard_block,
+					entry->count);
+			sb_issue_discard(sb, discard_block, entry->count);
+		}
+
 		err = ext4_mb_load_buddy(sb, entry->group, &e4b);
 		/* we expect to find existing buddy because it's pinned */
 		BUG_ON(err != 0);
@@ -2558,19 +2569,6 @@ static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 			page_cache_release(e4b.bd_bitmap_page);
 		}
 		ext4_unlock_group(sb, entry->group);
-		if (test_opt(sb, DISCARD)) {
-			ext4_fsblk_t discard_block;
-			struct ext4_super_block *es = EXT4_SB(sb)->s_es;
-
-			discard_block = (ext4_fsblk_t)entry->group *
-						EXT4_BLOCKS_PER_GROUP(sb)
-					+ entry->start_blk
-					+ le32_to_cpu(es->s_first_data_block);
-			trace_ext4_discard_blocks(sb,
-					(unsigned long long)discard_block,
-					entry->count);
-			sb_issue_discard(sb, discard_block, entry->count);
-		}
 		kmem_cache_free(ext4_free_ext_cachep, entry);
 		ext4_mb_release_desc(&e4b);
 	}
-- 
1.6.6.1.1.g974db.dirty

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