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Commit 4a770891 authored by Omar Sandoval's avatar Omar Sandoval Committed by Chris Mason
Browse files

Btrfs: fix parity scrub of RAID 5/6 with missing device 



When testing the previous patch, Zhao Lei reported a similar bug when
attempting to scrub a degraded RAID 5/6 filesystem with a missing
device, leading to NULL pointer dereferences from the RAID 5/6 parity
scrubbing code.

The first cause was the same as in the previous patch: attempting to
call bio_add_page() on a missing block device. To fix this,
scrub_extent_for_parity() can just mark the sectors on the missing
device as errors instead of attempting to read from it.

Additionally, the code uses scrub_remap_extent() to map the extent of
the corresponding data stripe, but the extent wasn't already mapped. If
scrub_remap_extent() finds a missing block device, it doesn't initialize
extent_dev, so we're left with a NULL struct btrfs_device. The solution
is to use btrfs_map_block() directly.

Reported-by: default avatarZhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent 73ff61db

fs/btrfs/scrub.c

+22 −4
Original line number Diff line number Diff line
@@ -2696,6 +2696,11 @@ static int scrub_extent_for_parity(struct scrub_parity *sparity, 
	u8 csum[BTRFS_CSUM_SIZE];

	u32 blocksize;



	if (dev->missing) {

		scrub_parity_mark_sectors_error(sparity, logical, len);

		return 0;

	}



	if (flags & BTRFS_EXTENT_FLAG_DATA) {

		blocksize = sctx->sectorsize;

	} else if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
@@ -2905,6 +2910,7 @@ static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx, 
	struct btrfs_root *root = fs_info->extent_root;

	struct btrfs_root *csum_root = fs_info->csum_root;

	struct btrfs_extent_item *extent;

	struct btrfs_bio *bbio = NULL;

	u64 flags;

	int ret;

	int slot;
@@ -2914,6 +2920,7 @@ static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx, 
	u64 extent_logical;

	u64 extent_physical;

	u64 extent_len;

	u64 mapped_length;

	struct btrfs_device *extent_dev;

	struct scrub_parity *sparity;

	int nsectors;
@@ -3037,10 +3044,21 @@ static noinline_for_stack int scrub_raid56_parity(struct scrub_ctx *sctx, 
			scrub_parity_mark_sectors_data(sparity, extent_logical,

						       extent_len);



			scrub_remap_extent(fs_info, extent_logical,

					   extent_len, &extent_physical,

					   &extent_dev,

					   &extent_mirror_num);

			mapped_length = extent_len;

			ret = btrfs_map_block(fs_info, READ, extent_logical,

					      &mapped_length, &bbio, 0);

			if (!ret) {

				if (!bbio || mapped_length < extent_len)

					ret = -EIO;

			}

			if (ret) {

				btrfs_put_bbio(bbio);

				goto out;

			}

			extent_physical = bbio->stripes[0].physical;

			extent_mirror_num = bbio->mirror_num;

			extent_dev = bbio->stripes[0].dev;

			btrfs_put_bbio(bbio);



			ret = btrfs_lookup_csums_range(csum_root,

						extent_logical,