tree 710a6440afd5503acc5234802b7f4369ec8d4600
parent 1d3c61c2eb3fe4f96d3192212f1bdcee49ea55aa
author Filipe Manana <fdmanana@suse.com> 1430835687 +0100
committer Chris Mason <clm@fb.com> 1431356350 -0700

Btrfs: fix crash after inode cache writeback failure

If the writeback of an inode cache failed we were unnecessarilly
attempting to release again the delalloc metadata that we previously
reserved. However attempting to do this a second time triggers an
assertion at drop_outstanding_extent() because we have no more
outstanding extents for our inode cache's inode. If we were able
to start writeback of the cache the reserved metadata space is
released at btrfs_finished_ordered_io(), even if an error happens
during writeback.

So make sure we don't repeat the metadata space release if writeback
started for our inode cache.

This issue was trivial to reproduce by running the fstest btrfs/088
with "-o inode_cache", which triggered the assertion leading to a
BUG() call and requiring a reboot in order to run the remaining
fstests. Trace produced by btrfs/088:

[255289.385904] BTRFS: assertion failed: BTRFS_I(inode)->outstanding_extents >= num_extents, file: fs/btrfs/extent-tree.c, line: 5276
[255289.388094] ------------[ cut here ]------------
[255289.389184] kernel BUG at fs/btrfs/ctree.h:4057!
[255289.390125] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
(...)
[255289.392068] Call Trace:
[255289.392068]  [<ffffffffa035e774>] drop_outstanding_extent+0x3d/0x6d [btrfs]
[255289.392068]  [<ffffffffa0364988>] btrfs_delalloc_release_metadata+0x54/0xe3 [btrfs]
[255289.392068]  [<ffffffffa03b4174>] btrfs_write_out_ino_cache+0x95/0xad [btrfs]
[255289.392068]  [<ffffffffa036f5c4>] btrfs_save_ino_cache+0x275/0x2dc [btrfs]
[255289.392068]  [<ffffffffa03e2d83>] commit_fs_roots.isra.12+0xaa/0x137 [btrfs]
[255289.392068]  [<ffffffff8107d33d>] ? trace_hardirqs_on+0xd/0xf
[255289.392068]  [<ffffffffa037841f>] ? btrfs_commit_transaction+0x4b1/0x9c9 [btrfs]
[255289.392068]  [<ffffffff814351a4>] ? _raw_spin_unlock+0x32/0x46
[255289.392068]  [<ffffffffa037842e>] btrfs_commit_transaction+0x4c0/0x9c9 [btrfs]
(...)

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>