xfs: Don't reference the EFI after it is freed

Checking the EFI for whether it is being released from recovery
after we've already released the known active reference is a mistake
worthy of a brown paper bag. Fix the (now) obvious use after free
that it can cause.

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c
index c0f375087efc3256cf5196ff08cdd2068ce18834..452920a3f03fb2e4405ce52e34587e55acfb7abe 100644 (file)
--- a/fs/xfs/xfs_extfree_item.c
+++ b/fs/xfs/xfs_extfree_item.c
@@ -305,11 +305,12 @@ xfs_efi_release(xfs_efi_log_item_t        *efip,
 {
        ASSERT(atomic_read(&efip->efi_next_extent) >= nextents);
        if (atomic_sub_and_test(nextents, &efip->efi_next_extent)) {
-               __xfs_efi_release(efip);
-
                /* recovery needs us to drop the EFI reference, too */
                if (test_bit(XFS_EFI_RECOVERED, &efip->efi_flags))
                        __xfs_efi_release(efip);
+
+               __xfs_efi_release(efip);
+               /* efip may now have been freed, do not reference it again. */
        }
 }