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    Subject[PATCH 3.12 005/142] ext4: fix BUG_ON in mb_free_blocks()
    Date
    From: Theodore Ts'o <tytso@mit.edu>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    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>
    Cc: stable@vger.kernel.org
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    ---
    fs/ext4/mballoc.c | 5 +++++
    1 file changed, 5 insertions(+)

    diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
    index 795d5afc1479..242226a87be7 100644
    --- a/fs/ext4/mballoc.c
    +++ b/fs/ext4/mballoc.c
    @@ -1398,6 +1398,8 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
    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. */
    @@ -3200,6 +3202,8 @@ static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
    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) {
    /*
    @@ -3214,6 +3218,7 @@ static void ext4_discard_allocated_blocks(struct ext4_allocation_context *ac)
    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)
    --
    2.1.0


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