On Wed, Mar 30, 2016 at 06:19:24PM +0200, Jan Kara wrote: > Huang has reported that in his powerfail testing he is seeing stale > block contents in some of recently allocated blocks although he mounts > ext4 in data=ordered mode. After some investigation I have found out > that indeed when delayed allocation is used, we don't add inode to > transaction's list of inodes needing flushing before commit. Originally > we were doing that but commit f3b59291a69d removed the logic with a > flawed argument that it is not needed. > > The problem is that although for delayed allocated blocks we write their > contents immediately after allocating them, there is no guarantee that > the IO scheduler or device doesn't reorder things and thus transaction > allocating blocks and attaching them to inode can reach stable storage > before actual block contents. Actually whenever we attach freshly > allocated blocks to inode using a written extent, we should add inode to > transaction's ordered inode list to make sure we properly wait for block > contents to be written before committing the transaction. So that is > what we do in this patch. This also handles other cases where stale data > exposure was possible - like filling hole via mmap in > data=ordered,nodelalloc mode. > > The only exception to the above rule are extending direct IO writes where > blkdev_direct_IO() waits for IO to complete before increasing i_size and > thus stale data exposure is not possible. For now we don't complicate > the code with optimizing this special case since the overhead is pretty > low. In case this is observed to be a performance problem we can always > handle it using a special flag to ext4_map_blocks(). > > CC: stable@xxxxxxxxxxxxxxx > Fixes: f3b59291a69d0b734be1fc8be489fef2dd846d3d > Reported-by: "HUANG Weller (CM/ESW12-CN)" <Weller.Huang@xxxxxxxxxxxx> > Tested-by: "HUANG Weller (CM/ESW12-CN)" <Weller.Huang@xxxxxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> Applied, thanks. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
