ext4: fix reference counting bug on block allocation error

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>
Cc: stable@vger.kernel.org

1 files changed, 3 insertions, 14 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 77249e1f5c3a..11562161e24a 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2943,7 +2943,7 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
                 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);
@@ -2952,7 +2952,7 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
                 ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
                 err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
                 if (!err)
-                        err = -EAGAIN;
+                        err = -EFSCORRUPTED;
                 goto out_err;
         }
 
@@ -4517,18 +4517,7 @@ 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 {