On Wed, Apr 22, 2015 at 04:06:16PM +0200, Lukas Czerner wrote: > Currently it is possible to lose whole file system block worth of data > when we hit the specific interaction with unwritten and delayed extents > in status extent tree. > > The problem is that when we insert delayed extent into extent status > tree the only way to get rid of it is when we write out delayed buffer. > However there is a limitation in the extent status tree implementation > so that when inserting unwritten extent should there be even a single > delayed block the whole unwritten extent would be marked as delayed. > > At this point, there is no way to get rid of the delayed extents, > because there are no delayed buffers to write out. So when a we write > into said unwritten extent we will convert it to written, but it still > remains delayed. > > When we try to write into that block later ext4_da_map_blocks() will set > the buffer new and delayed and map it to invalid block which causes > the rest of the block to be zeroed loosing already written data. > > For now we can fix this by simply not allowing to set delayed status on > written extent in the extent status tree. Also add WARN_ON() to make > sure that we notice if this happens in the future. > > This problem can be easily reproduced by running the following xfs_io. > > xfs_io -f -c "pwrite -S 0xaa 4096 2048" \ > -c "falloc 0 131072" \ > -c "pwrite -S 0xbb 65536 2048" \ > -c "fsync" /mnt/test/fff > > echo 3 > /proc/sys/vm/drop_caches > xfs_io -c "pwrite -S 0xdd 67584 2048" /mnt/test/fff > > This can be theoretically also reproduced by at random by running fsx, > but it's not very reliable, though on machines with bigger page size > (like ppc) this can be seen more often (especially xfstest generic/127) > > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx 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
