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    Subject[PATCH 3.16 074/346] ext4: fix reference counting bug on block allocation error
    3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Vegard Nossum <vegard.nossum@oracle.com>

    commit 554a5ccc4e4a20c5f3ec859de0842db4b4b9c77e upstream.

    If we hit this error when mounted with errors=continue or
    errors=remount-ro:

    EXT4-fs error (device loop0): ext4_mb_mark_diskspace_used:2940: comm ext4.exe: Allocating blocks 5090-6081 which overlap fs metadata

    then ext4_mb_new_blocks() will call ext4_mb_release_context() and try to
    continue. However, ext4_mb_release_context() is the wrong thing to call
    here since we are still actually using the allocation context.

    Instead, just error out. We could retry the allocation, but there is a
    possibility of getting stuck in an infinite loop instead, so this seems
    safer.

    [ Fixed up so we don't return EAGAIN to userspace. --tytso ]

    Fixes: 8556e8f3b6 ("ext4: Don't allow new groups to be added during block allocation")
    Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    [bwh: Backported to 3.16: use EIO instead of EFSCORRUPTED]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    fs/ext4/mballoc.c | 17 +++--------------
    1 file changed, 3 insertions(+), 14 deletions(-)

    --- a/fs/ext4/mballoc.c
    +++ b/fs/ext4/mballoc.c
    @@ -2911,7 +2911,7 @@ ext4_mb_mark_diskspace_used(struct ext4_
    ext4_error(sb, "Allocating blocks %llu-%llu which overlap "
    "fs metadata", block, block+len);
    /* File system mounted not to panic on error
    - * Fix the bitmap and repeat the block allocation
    + * Fix the bitmap and return EFSCORRUPTED
    * We leak some of the blocks here.
    */
    ext4_lock_group(sb, ac->ac_b_ex.fe_group);
    @@ -2920,7 +2920,7 @@ ext4_mb_mark_diskspace_used(struct ext4_
    ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
    err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
    if (!err)
    - err = -EAGAIN;
    + err = -EIO;
    goto out_err;
    }

    @@ -4489,18 +4489,7 @@ repeat:
    }
    if (likely(ac->ac_status == AC_STATUS_FOUND)) {
    *errp = ext4_mb_mark_diskspace_used(ac, handle, reserv_clstrs);
    - if (*errp == -EAGAIN) {
    - /*
    - * drop the reference that we took
    - * in ext4_mb_use_best_found
    - */
    - ext4_mb_release_context(ac);
    - ac->ac_b_ex.fe_group = 0;
    - ac->ac_b_ex.fe_start = 0;
    - ac->ac_b_ex.fe_len = 0;
    - ac->ac_status = AC_STATUS_CONTINUE;
    - goto repeat;
    - } else if (*errp) {
    + if (*errp) {
    ext4_discard_allocated_blocks(ac);
    goto errout;
    } else {
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