On 15.05.2018 10:36, Qu Wenruo wrote: > As btrfs(5) specified: > > Note > If nodatacow or nodatasum are enabled, compression is disabled. > > If NODATASUM or NODATACOW set, we should not compress the extent. > > Normally NODATACOW is detected properly in run_delalloc_range() so > compression won't happen for NODATACOW. > > However for NODATASUM we don't have any check, and it can cause > compressed extent without csum pretty easily, just by: > ------ > mkfs.btrfs -f $dev > mount $dev $mnt -o nodatasum > touch $mnt/foobar > mount -o remount,datasum,compress $mnt > xfs_io -f -c "pwrite 0 128K" $mnt/foobar > ------ > > And in fact, we have bug report about corrupted compressed extent > without proper data checksum so even RAID1 can't recover the corruption. > (https://bugzilla.kernel.org/show_bug.cgi?id=199707) > > Running compression without proper checksum could cause more damage when > corruption happens, so there is no need to allow compression for > NODATACSUM. > > Reported-by: James Harvey <jamespharvey20@xxxxxxxxx> > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> > --- > fs/btrfs/inode.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c > index d241285a0d2a..dbef3f404559 100644 > --- a/fs/btrfs/inode.c > +++ b/fs/btrfs/inode.c > @@ -396,6 +396,14 @@ static inline int inode_need_compress(struct inode *inode, u64 start, u64 end) > { > struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); > > + /* > + * Btrfs doesn't support compression without csum or CoW. > + * This should have the highest priority. > + */ > + if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW || > + BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM) > + return 0; > + How is this not buggy, given that if inode_need_compress as called from compress_file_range will return zero, meaning we jump to cont: label. Then in the case of an inline extent we can execute : ret = cow_file_range_inline(inode, start, end, total_compressed, compress_type, pages); where compress_type would have been set at the beginning of the function unconditionally to fs_info->compress_type. For non-inline extents I guess we are ok, given that will_compress will not be set. However, this code is rather messy and I'm not sure it's well defined what's going to happen in this case with inline extents. OTOH, I think there is something fundamentally wrong in calling inode_need_compress in compress_file_range. I.e they work at different abstractions. IMO compress_file_range should only be called if we know we have to compress the range. So looking around the code in run_delalloc_range (the only function which calls cow_file_range_async) we already have : } else if (!inode_need_compress(inode, start, end)) { ret = cow_file_range(inode, locked_page, start, end, end, page_started, nr_written, 1, NULL); and in the else branch we have the cow_file_range_async. So the code is sort of half-way there to actually decoupling compression checking from performing the actual compression. > /* force compress */ > if (btrfs_test_opt(fs_info, FORCE_COMPRESS)) > return 1; One more thing, in inode_need_compress shouldn't the inode specific checks come first something like : static inline int inode_need_compress(struct inode *inode, u64 start, u64 end) { struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); /* defrag ioctl */ if (BTRFS_I(inode)->defrag_compress) return 1; /* bad compression ratios */ if (BTRFS_I(inode)->flags & BTRFS_INODE_NOCOMPRESS) return 0; /* force compress */ if (btrfs_test_opt(fs_info, FORCE_COMPRESS)) return 1; if (btrfs_test_opt(fs_info, COMPRESS) || BTRFS_I(inode)->flags & BTRFS_INODE_COMPRESS || BTRFS_I(inode)->prop_compress) return btrfs_compress_heuristic(inode, start, end); return 0; } > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
