There is a small window where an eb can have no IO bits set on it, which could potentially result in extent_buffer_under_io() returning false when we want it to return true, which could result in not fun things happening. So in order to protect this case we need to hold the refs_lock when we make this transition to make sure we get reliable results out of extent_buffer_udner_io(). Thanks, Btrfs: lock the transition from dirty to writeback for an eb
There is a small window where an eb can have no IO bits set on it, which could potentially result in extent_buffer_under_io() returning false when we want it to return true, which could result in not fun things happening. So in order to protect this case we need to hold the refs_lock when we make this transition to make sure we get reliable results out of extent_buffer_udner_io(). Thanks, Signed-off-by: Josef Bacik <[email protected]> --- fs/btrfs/extent_io.c | 9 +++++++++ 1 files changed, 9 insertions(+), 0 deletions(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 20440ea..669219b 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3077,8 +3077,15 @@ static int lock_extent_buffer_for_io(struct extent_buffer *eb, } } + /* + * We need to do this to prevent races in people who check if the eb is + * under IO since we can end up having no IO bits set for a short period + * of time. + */ + spin_lock(&eb->refs_lock); if (test_and_clear_bit(EXTENT_BUFFER_DIRTY, &eb->bflags)) { set_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags); + spin_unlock(&eb->refs_lock); btrfs_set_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN); spin_lock(&fs_info->delalloc_lock); if (fs_info->dirty_metadata_bytes >= eb->len) @@ -3087,6 +3094,8 @@ static int lock_extent_buffer_for_io(struct extent_buffer *eb, WARN_ON(1); spin_unlock(&fs_info->delalloc_lock); ret = 1; + } else { + spin_unlock(&eb->refs_lock); } btrfs_tree_unlock(eb); -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
