From: Filipe Manana Date: Mon, 13 Oct 2014 11:28:37 +0000 (+0100) Subject: Btrfs: deal with convert_extent_bit errors to avoid fs corruption X-Git-Tag: omap-for-v3.19/fixes-rc1~111^2~34 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=663dfbb07774e0fe1049e8db3054a08500122f18;p=pandora-kernel.git Btrfs: deal with convert_extent_bit errors to avoid fs corruption When committing a transaction or a log, we look for btree extents that need to be durably persisted by searching for ranges in a io tree that have some bits set (EXTENT_DIRTY or EXTENT_NEW). We then attempt to clear those bits and set the EXTENT_NEED_WAIT bit, with calls to the function convert_extent_bit, and then start writeback for the extents. That function however can return an error (at the moment only -ENOMEM is possible, specially when it does GFP_ATOMIC allocation requests through alloc_extent_state_atomic) - that means the ranges didn't got the EXTENT_NEED_WAIT bit set (or at least not for the whole range), which in turn means a call to btrfs_wait_marked_extents() won't find those ranges for which we started writeback, causing a transaction commit or a log commit to persist a new superblock without waiting for the writeback of extents in that range to finish first. Therefore if a crash happens after persisting the new superblock and before writeback finishes, we have a superblock pointing to roots that weren't fully persisted or roots that point to nodes or leafs that weren't fully persisted, causing all sorts of unexpected/bad behaviour as we endup reading garbage from disk or the content of some node/leaf from a past generation that got cowed or deleted and is no longer valid (for this later case we end up getting error messages like "parent transid verify failed on X wanted Y found Z" when reading btree nodes/leafs from disk). Signed-off-by: Filipe Manana Signed-off-by: Chris Mason --- Reading git-diff-tree failed