From a13467ee7ae3742f23f0bef0cafa168312a94cb4 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Fri, 11 Mar 2022 15:38:49 +0800 Subject: [PATCH] btrfs: scrub: move scrub_remap_extent() call into scrub_extent() [SUSPICIOUS CODE] When refactoring scrub code, I noticed a very strange behavior around scrub_remap_extent(): if (sctx->is_dev_replace) scrub_remap_extent(fs_info, cur_logical, scrub_len, &cur_physical, &target_dev, &cur_mirror); As replace target is a 1:1 copy of the source device, thus physical offset inside the target should be the same as physical inside source, thus this remap call makes no sense to me. [REAL FUNCTIONALITY] After more investigation, the function name scrub_remap_extent() doesn't tell anything of the truth, nor does its if () condition. The real story behind this function is that, for scrub_pages() we never expect missing device, even for replacing missing device. What scrub_remap_extent() is really doing is to find a live mirror, and make later scrub_pages() to read data from the good copy, other than from the missing device and increase error counters unnecessarily. [IMPROVEMENT] We have no need to bother scrub_remap_extent() in scrub_simple_mirror() at all, we only need to call it before we call scrub_pages(). And rename the function to scrub_find_live_copy(), add extra comments on them. By this we can remove one parameter from scrub_extent(), and reduce the unnecessary calls to scrub_remap_extent() for regular replace. Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- fs/btrfs/scrub.c | 62 +++++++++++++++++++++++++++--------------------- 1 file changed, 35 insertions(+), 27 deletions(-) diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index 9767d77e2493..e7b0323e6efd 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -233,11 +233,11 @@ static int scrub_sectors(struct scrub_ctx *sctx, u64 logical, u32 len, static void scrub_bio_end_io(struct bio *bio); static void scrub_bio_end_io_worker(struct work_struct *work); static void scrub_block_complete(struct scrub_block *sblock); -static void scrub_remap_extent(struct btrfs_fs_info *fs_info, - u64 extent_logical, u32 extent_len, - u64 *extent_physical, - struct btrfs_device **extent_dev, - int *extent_mirror_num); +static void scrub_find_good_copy(struct btrfs_fs_info *fs_info, + u64 extent_logical, u32 extent_len, + u64 *extent_physical, + struct btrfs_device **extent_dev, + int *extent_mirror_num); static int scrub_add_sector_to_wr_bio(struct scrub_ctx *sctx, struct scrub_sector *sector); static void scrub_wr_submit(struct scrub_ctx *sctx); @@ -2187,7 +2187,7 @@ static void scrub_missing_raid56_pages(struct scrub_block *sblock) * We shouldn't be scrubbing a missing device. Even for dev * replace, we should only get here for RAID 5/6. We either * managed to mount something with no mirrors remaining or - * there's a bug in scrub_remap_extent()/btrfs_map_block(). + * there's a bug in scrub_find_good_copy()/btrfs_map_block(). */ goto bioc_out; } @@ -2510,8 +2510,11 @@ static int scrub_find_csum(struct scrub_ctx *sctx, u64 logical, u8 *csum) static int scrub_extent(struct scrub_ctx *sctx, struct map_lookup *map, u64 logical, u32 len, u64 physical, struct btrfs_device *dev, u64 flags, - u64 gen, int mirror_num, u64 physical_for_dev_replace) + u64 gen, int mirror_num) { + struct btrfs_device *src_dev = dev; + u64 src_physical = physical; + int src_mirror = mirror_num; int ret; u8 csum[BTRFS_CSUM_SIZE]; u32 blocksize; @@ -2539,6 +2542,18 @@ static int scrub_extent(struct scrub_ctx *sctx, struct map_lookup *map, WARN_ON(1); } + /* + * For dev-replace case, we can have @dev being a missing device. + * Regular scrub will avoid its execution on missing device at all, + * as that would trigger tons of read error. + * + * Reading from missing device will cause read error counts to + * increase unnecessarily. + * So here we change the read source to a good mirror. + */ + if (sctx->is_dev_replace && !dev->bdev) + scrub_find_good_copy(sctx->fs_info, logical, len, &src_physical, + &src_dev, &src_mirror); while (len) { u32 l = min(len, blocksize); int have_csum = 0; @@ -2549,15 +2564,15 @@ static int scrub_extent(struct scrub_ctx *sctx, struct map_lookup *map, if (have_csum == 0) ++sctx->stat.no_csum; } - ret = scrub_sectors(sctx, logical, l, physical, dev, flags, gen, - mirror_num, have_csum ? csum : NULL, - physical_for_dev_replace); + ret = scrub_sectors(sctx, logical, l, src_physical, src_dev, + flags, gen, src_mirror, + have_csum ? csum : NULL, physical); if (ret) return ret; len -= l; logical += l; physical += l; - physical_for_dev_replace += l; + src_physical += l; } return 0; } @@ -3244,14 +3259,11 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx, path.skip_locking = 1; /* Go through each extent items inside the logical range */ while (cur_logical < logical_end) { - int cur_mirror = mirror_num; - struct btrfs_device *target_dev = device; u64 extent_start; u64 extent_len; u64 extent_flags; u64 extent_gen; u64 scrub_len; - u64 cur_physical; /* Canceled? */ if (atomic_read(&fs_info->scrub_cancel_req) || @@ -3307,11 +3319,7 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx, scrub_len = min(min(extent_start + extent_len, logical_end), cur_logical + max_length) - cur_logical; - cur_physical = cur_logical - logical_start + physical; - if (sctx->is_dev_replace) - scrub_remap_extent(fs_info, cur_logical, scrub_len, - &cur_physical, &target_dev, &cur_mirror); if (extent_flags & BTRFS_EXTENT_FLAG_DATA) { ret = btrfs_lookup_csums_range(csum_root, cur_logical, cur_logical + scrub_len - 1, @@ -3331,10 +3339,10 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx, cur_logical += scrub_len; continue; } - ret = scrub_extent(sctx, map, cur_logical, scrub_len, cur_physical, - target_dev, extent_flags, extent_gen, - cur_mirror, cur_logical - logical_start + - physical); + ret = scrub_extent(sctx, map, cur_logical, scrub_len, + cur_logical - logical_start + physical, + device, extent_flags, extent_gen, + mirror_num); scrub_free_csums(sctx); if (ret) break; @@ -4342,11 +4350,11 @@ int btrfs_scrub_progress(struct btrfs_fs_info *fs_info, u64 devid, return dev ? (sctx ? 0 : -ENOTCONN) : -ENODEV; } -static void scrub_remap_extent(struct btrfs_fs_info *fs_info, - u64 extent_logical, u32 extent_len, - u64 *extent_physical, - struct btrfs_device **extent_dev, - int *extent_mirror_num) +static void scrub_find_good_copy(struct btrfs_fs_info *fs_info, + u64 extent_logical, u32 extent_len, + u64 *extent_physical, + struct btrfs_device **extent_dev, + int *extent_mirror_num) { u64 mapped_length; struct btrfs_io_context *bioc = NULL; -- GitLab