Commits
Liu Bo committed 48ec47364b6
Btrfs: fix a crash when running balance and defrag concurrently Running balance and defrag concurrently can end up with a crash: kernel BUG at fs/btrfs/relocation.c:4528! RIP: 0010:[<ffffffffa01ac33b>] [<ffffffffa01ac33b>] btrfs_reloc_cow_block+ 0x1eb/0x230 [btrfs] Call Trace: [<ffffffffa01398c1>] ? update_ref_for_cow+0x241/0x380 [btrfs] [<ffffffffa0180bad>] ? copy_extent_buffer+0xad/0x110 [btrfs] [<ffffffffa0139da1>] __btrfs_cow_block+0x3a1/0x520 [btrfs] [<ffffffffa013a0b6>] btrfs_cow_block+0x116/0x1b0 [btrfs] [<ffffffffa013ddad>] btrfs_search_slot+0x43d/0x970 [btrfs] [<ffffffffa0153c57>] btrfs_lookup_file_extent+0x37/0x40 [btrfs] [<ffffffffa0172a5e>] __btrfs_drop_extents+0x11e/0xae0 [btrfs] [<ffffffffa013b3fd>] ? generic_bin_search.constprop.39+0x8d/0x1a0 [btrfs] [<ffffffff8117d14a>] ? kmem_cache_alloc+0x1da/0x200 [<ffffffffa0138e7a>] ? btrfs_alloc_path+0x1a/0x20 [btrfs] [<ffffffffa0173ef0>] btrfs_drop_extents+0x60/0x90 [btrfs] [<ffffffffa016b24d>] relink_extent_backref+0x2ed/0x780 [btrfs] [<ffffffffa0162fe0>] ? btrfs_submit_bio_hook+0x1e0/0x1e0 [btrfs] [<ffffffffa01b8ed7>] ? iterate_inodes_from_logical+0x87/0xa0 [btrfs] [<ffffffffa016b909>] btrfs_finish_ordered_io+0x229/0xac0 [btrfs] [<ffffffffa016c3b5>] finish_ordered_fn+0x15/0x20 [btrfs] [<ffffffffa018cbe5>] worker_loop+0x125/0x4e0 [btrfs] [<ffffffffa018cac0>] ? btrfs_queue_worker+0x300/0x300 [btrfs] [<ffffffff81075ea0>] kthread+0xc0/0xd0 [<ffffffff81075de0>] ? insert_kthread_work+0x40/0x40 [<ffffffff8164796c>] ret_from_fork+0x7c/0xb0 [<ffffffff81075de0>] ? insert_kthread_work+0x40/0x40 ---------------------------------------------------------------------- It turns out to be that balance operation will bump root's @last_snapshot, which enables snapshot-aware defrag path, and backref walking stuff will find data reloc tree as refs' parent, and hit the BUG_ON() during COW. As data reloc tree's data is just for relocation purpose, and will be deleted right after relocation is done, it's unnecessary to walk those refs belonged to data reloc tree, it'd be better to skip them. Signed-off-by: Liu Bo <bo.li.liu@oracle.com> Signed-off-by: Josef Bacik <jbacik@fusionio.com> Signed-off-by: Chris Mason <chris.mason@fusionio.com>