4.9-stable review patch. If anyone has any objections, please let me know.
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From: Qu Wenruo wqu@suse.com
commit ac0b4145d662a3b9e34085dea460fb06ede9b69b upstream.
[BUG] Btrfs can create compressed extent without checksum (even though it shouldn't), and if we then try to replace device containing such extent, the result device will contain all the uncompressed data instead of the compressed one.
Test case already submitted to fstests: https://patchwork.kernel.org/patch/10442353/
[CAUSE] When handling compressed extent without checksum, device replace will goe into copy_nocow_pages() function.
In that function, btrfs will get all inodes referring to this data extents and then use find_or_create_page() to get pages direct from that inode.
The problem here is, pages directly from inode are always uncompressed. And for compressed data extent, they mismatch with on-disk data. Thus this leads to corrupted compressed data extent written to replace device.
[FIX] In this attempt, we could just remove the "optimization" branch, and let unified scrub_pages() to handle it.
Although scrub_pages() won't bother reusing page cache, it will be a little slower, but it does the correct csum checking and won't cause such data corruption caused by "optimization".
Note about the fix: this is the minimal fix that can be backported to older stable trees without conflicts. The whole callchain from copy_nocow_pages() can be deleted, and will be in followup patches.
Fixes: ff023aac3119 ("Btrfs: add code to scrub to copy read data to another disk") CC: stable@vger.kernel.org # 4.4+ Reported-by: James Harvey jamespharvey20@gmail.com Reviewed-by: James Harvey jamespharvey20@gmail.com Signed-off-by: Qu Wenruo wqu@suse.com [ remove code removal, add note why ] Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/scrub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -2519,7 +2519,7 @@ static int scrub_extent(struct scrub_ctx have_csum = scrub_find_csum(sctx, logical, csum); if (have_csum == 0) ++sctx->stat.no_csum; - if (sctx->is_dev_replace && !have_csum) { + if (0 && sctx->is_dev_replace && !have_csum) { ret = copy_nocow_pages(sctx, logical, l, mirror_num, physical_for_dev_replace);