[PATCH 3.16 063/125] ext4: fix BUG_ON in mb_free_blocks()

Greg Kroah-Hartman
2014-09-03T23:08:15Z

From: Theodore Ts'o <tytso@mit.edu>

commit c99d1e6e83b06744c75d9f5e491ed495a7086b7b upstream.

If we suffer a block allocation failure (for example due to a memory
allocation failure), it's possible that we will call
ext4_discard_allocated_blocks() before we've actually allocated any
blocks. In that case, fe_len and fe_start in ac->ac_f_ex will still
be zero, and this will result in mb_free_blocks(inode, e4b, 0, 0)
triggering the BUG_ON on mb_free_blocks():

BUG_ON(last >= (sb->s_blocksize << 3));

Fix this by bailing out of ext4_discard_allocated_blocks() if fs_len
is zero.

Also fix a missing ext4_mb_unload_buddy() call in
ext4_discard_allocated_blocks().

Google-Bug-Id: 16844242

Fixes: 86f0afd463215fc3e58020493482faa4ac3a4d69
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext4/mballoc.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1412,6 +1412,8 @@ static void mb_free_blocks(struct inode
int last = first + count - 1;
struct super_block *sb = e4b->bd_sb;

+ if (WARN_ON(count == 0))
+ return;
BUG_ON(last >= (sb->s_blocksize << 3));
assert_spin_locked(ext4_group_lock_ptr(sb, e4b->bd_group));
/* Don't bother if the block group is corrupt. */
@@ -3220,6 +3222,8 @@ static void ext4_discard_allocated_block
int err;

if (pa == NULL) {
+ if (ac->ac_f_ex.fe_len == 0)
+ return;
err = ext4_mb_load_buddy(ac->ac_sb, ac->ac_f_ex.fe_group, &e4b);
if (err) {
/*
@@ -3234,6 +3238,7 @@ static void ext4_discard_allocated_block
mb_free_blocks(ac->ac_inode, &e4b, ac->ac_f_ex.fe_start,
ac->ac_f_ex.fe_len);
ext4_unlock_group(ac->ac_sb, ac->ac_f_ex.fe_group);
+ ext4_mb_unload_buddy(&e4b);
return;
}
if (pa->pa_type == MB_INODE_PA)