From: Josef Bacik josef@toxicpanda.com
commit c962098ca4af146f2625ed64399926a098752c9c upstream.
In production we were seeing a variety of WARN_ON()'s in the extent_map code, specifically in btrfs_drop_extent_map_range() when we have to call add_extent_mapping() for our second split.
Consider the following extent map layout
PINNED [0 16K) [32K, 48K)
and then we call btrfs_drop_extent_map_range for [0, 36K), with skip_pinned == true. The initial loop will have
start = 0 end = 36K len = 36K
we will find the [0, 16k) extent, but since we are pinned we will skip it, which has this code
start = em_end; if (end != (u64)-1) len = start + len - em_end;
em_end here is 16K, so now the values are
start = 16K len = 16K + 36K - 16K = 36K
len should instead be 20K. This is a problem when we find the next extent at [32K, 48K), we need to split this extent to leave [36K, 48k), however the code for the split looks like this
split->start = start + len; split->len = em_end - (start + len);
In this case we have
em_end = 48K split->start = 16K + 36K // this should be 16K + 20K split->len = 48K - (16K + 36K) // this overflows as 16K + 36K is 52K
and now we have an invalid extent_map in the tree that potentially overlaps other entries in the extent map. Even in the non-overlapping case we will have split->start set improperly, which will cause problems with any block related calculations.
We don't actually need len in this loop, we can simply use end as our end point, and only adjust start up when we find a pinned extent we need to skip.
Adjust the logic to do this, which keeps us from inserting an invalid extent map.
We only skip_pinned in the relocation case, so this is relatively rare, except in the case where you are running relocation a lot, which can happen with auto relocation on.
Fixes: 55ef68990029 ("Btrfs: Fix btrfs_drop_extent_cache for skip pinned case") CC: stable@vger.kernel.org # 4.14+ Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Josef Bacik josef@toxicpanda.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/extent_map.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
--- a/fs/btrfs/extent_map.c +++ b/fs/btrfs/extent_map.c @@ -758,8 +758,6 @@ void btrfs_drop_extent_map_range(struct
if (skip_pinned && test_bit(EXTENT_FLAG_PINNED, &em->flags)) { start = em_end; - if (end != (u64)-1) - len = start + len - em_end; goto next; }
@@ -827,8 +825,8 @@ void btrfs_drop_extent_map_range(struct if (!split) goto remove_em; } - split->start = start + len; - split->len = em_end - (start + len); + split->start = end; + split->len = em_end - end; split->block_start = em->block_start; split->flags = flags; split->compress_type = em->compress_type;