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From: Theodore Ts'o <tytso@mit.edu>
Date: Tue, 20 Apr 2010 20:51:59 +0000 (-0400)
Subject: ext4: Issue the discard operation *before* releasing the blocks to be reused
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=b90f687018e6d6c77d981b09203780f7001407e5

ext4: Issue the discard operation *before* releasing the blocks to be reused

[ backported to 2.6.3[23] ]

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@mit.edu>
---

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 54df209..e5ab41b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2534,6 +2534,20 @@ 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;
+			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);
+		}
+
 		err = ext4_mb_load_buddy(sb, entry->group, &e4b);
 		/* we expect to find existing buddy because it's pinned */
 		BUG_ON(err != 0);
@@ -2555,19 +2566,6 @@ 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);
 	}