ext4: Issue the discard operation *before* releasing the blocks to be reused
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 54df209d..e5ab41b 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2534,6 +2534,17 @@
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);
@@ -2555,16 +2566,6 @@
page_cache_release(e4b.bd_bitmap_page);
}
ext4_unlock_group(sb, entry->group);
- 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);
- }
kmem_cache_free(ext4_free_ext_cachep, entry);
ext4_mb_release_desc(&e4b);
}