[PATCH AUTOSEL 4.19 041/244] btrfs: fix panic during relocation after ENOSPC before writeback happens

Sasha Levin
2019-05-22T19:45:07Z

From: Josef Bacik <josef@toxicpanda.com>

[ Upstream commit ff612ba7849964b1898fd3ccd1f56941129c6aab ]

We've been seeing the following sporadically throughout our fleet

panic: kernel BUG at fs/btrfs/relocation.c:4584!
netversion: 5.0-0
Backtrace:
#0 [ffffc90003adb880] machine_kexec at ffffffff81041da8
#1 [ffffc90003adb8c8] __crash_kexec at ffffffff8110396c
#2 [ffffc90003adb988] crash_kexec at ffffffff811048ad
#3 [ffffc90003adb9a0] oops_end at ffffffff8101c19a
#4 [ffffc90003adb9c0] do_trap at ffffffff81019114
#5 [ffffc90003adba00] do_error_trap at ffffffff810195d0
#6 [ffffc90003adbab0] invalid_op at ffffffff81a00a9b
[exception RIP: btrfs_reloc_cow_block+692]
RIP: ffffffff8143b614 RSP: ffffc90003adbb68 RFLAGS: 00010246
RAX: fffffffffffffff7 RBX: ffff8806b9c32000 RCX: ffff8806aad00690
RDX: ffff880850b295e0 RSI: ffff8806b9c32000 RDI: ffff88084f205bd0
RBP: ffff880849415000 R8: ffffc90003adbbe0 R9: ffff88085ac90000
R10: ffff8805f7369140 R11: 0000000000000000 R12: ffff880850b295e0
R13: ffff88084f205bd0 R14: 0000000000000000 R15: 0000000000000000
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#7 [ffffc90003adbbb0] __btrfs_cow_block at ffffffff813bf1cd
#8 [ffffc90003adbc28] btrfs_cow_block at ffffffff813bf4b3
#9 [ffffc90003adbc78] btrfs_search_slot at ffffffff813c2e6c

The way relocation moves data extents is by creating a reloc inode and
preallocating extents in this inode and then copying the data into these
preallocated extents. Once we've done this for all of our extents,
we'll write out these dirty pages, which marks the extent written, and
goes into btrfs_reloc_cow_block(). From here we get our current
reloc_control, which _should_ match the reloc_control for the current
block group we're relocating.

However if we get an ENOSPC in this path at some point we'll bail out,
never initiating writeback on this inode. Not a huge deal, unless we
happen to be doing relocation on a different block group, and this block
group is now rc->stage == UPDATE_DATA_PTRS. This trips the BUG_ON() in
btrfs_reloc_cow_block(), because we expect to be done modifying the data
inode. We are in fact done modifying the metadata for the data inode
we're currently using, but not the one from the failed block group, and
thus we BUG_ON().

(This happens when writeback finishes for extents from the previous
group, when we are at btrfs_finish_ordered_io() which updates the data
reloc tree (inode item, drops/adds extent items, etc).)

Fix this by writing out the reloc data inode always, and then breaking
out of the loop after that point to keep from tripping this BUG_ON()
later.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
[ add note from Filipe ]
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/relocation.c | 31 ++++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 0526b6c473c79..5d57ed6293455 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -4289,27 +4289,36 @@ int btrfs_relocate_block_group(struct btrfs_fs_info *fs_info, u64 group_start)
mutex_lock(&fs_info->cleaner_mutex);
ret = relocate_block_group(rc);
mutex_unlock(&fs_info->cleaner_mutex);
- if (ret < 0) {
+ if (ret < 0)
err = ret;
- goto out;
- }
-
- if (rc->extents_found == 0)
- break;
-
- btrfs_info(fs_info, "found %llu extents", rc->extents_found);

+ /*
+ * We may have gotten ENOSPC after we already dirtied some
+ * extents. If writeout happens while we're relocating a
+ * different block group we could end up hitting the
+ * BUG_ON(rc->stage == UPDATE_DATA_PTRS) in
+ * btrfs_reloc_cow_block. Make sure we write everything out
+ * properly so we don't trip over this problem, and then break
+ * out of the loop if we hit an error.
+ */
if (rc->stage == MOVE_DATA_EXTENTS && rc->found_file_extent) {
ret = btrfs_wait_ordered_range(rc->data_inode, 0,
(u64)-1);
- if (ret) {
+ if (ret)
err = ret;
- goto out;
- }
invalidate_mapping_pages(rc->data_inode->i_mapping,
0, -1);
rc->stage = UPDATE_DATA_PTRS;
}
+
+ if (err < 0)
+ goto out;
+
+ if (rc->extents_found == 0)
+ break;
+
+ btrfs_info(fs_info, "found %llu extents", rc->extents_found);
+
}

WARN_ON(rc->block_group->pinned > 0);
--
2.20.1