kernel/linux.git/fs/btrfs/raid56.c, branch linux-6.0.y

btrfs: raid56: properly handle the error when unable to find the missing stripe

2022-11-26T08:27:18+00:00

[ Upstream commit f15fb2cd979a07fbfc666e2f04b8b30ec9233b2a ] In raid56_alloc_missing_rbio(), if we can not determine where the missing device is inside the full stripe, we just BUG_ON(). This is not necessary especially the only caller inside scrub.c is already properly checking the return value, and will treat it as a memory allocation failure. Fix the error handling by: - Add an extra warning for the reason Although personally speaking it may be better to be an ASSERT(). - Properly free the allocated rbio Signed-off-by: Qu Wenruo Signed-off-by: David Sterba Signed-off-by: Sasha Levin

Merge tag 'for-5.20-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux

2022-08-03T21:54:52+00:00

Pull btrfs updates from David Sterba: "This brings some long awaited changes, the send protocol bump, otherwise lots of small improvements and fixes. The main core part is reworking bio handling, cleaning up the submission and endio and improving error handling. There are some changes outside of btrfs adding helpers or updating API, listed at the end of the changelog. Features: - sysfs: - export chunk size, in debug mode add tunable for setting its size - show zoned among features (was only in debug mode) - show commit stats (number, last/max/total duration) - send protocol updated to 2 - new commands: - ability write larger data chunks than 64K - send raw compressed extents (uses the encoded data ioctls), ie. no decompression on send side, no compression needed on receive side if supported - send 'otime' (inode creation time) among other timestamps - send file attributes (a.k.a file flags and xflags) - this is first version bump, backward compatibility on send and receive side is provided - there are still some known and wanted commands that will be implemented in the near future, another version bump will be needed, however we want to minimize that to avoid causing usability issues - print checksum type and implementation at mount time - don't print some messages at mount (mentioned as people asked about it), we want to print messages namely for new features so let's make some space for that - big metadata - this has been supported for a long time and is not a feature that's worth mentioning - skinny metadata - same reason, set by default by mkfs Performance improvements: - reduced amount of reserved metadata for delayed items - when inserted items can be batched into one leaf - when deleting batched directory index items - when deleting delayed items used for deletion - overall improved count of files/sec, decreased subvolume lock contention - metadata item access bounds checker micro-optimized, with a few percent of improved runtime for metadata-heavy operations - increase direct io limit for read to 256 sectors, improved throughput by 3x on sample workload Notable fixes: - raid56 - reduce parity writes, skip sectors of stripe when there are no data updates - restore reading from on-disk data instead of using stripe cache, this reduces chances to damage correct data due to RMW cycle - refuse to replay log with unknown incompat read-only feature bit set - zoned - fix page locking when COW fails in the middle of allocation - improved tracking of active zones, ZNS drives may limit the number and there are ENOSPC errors due to that limit and not actual lack of space - adjust maximum extent size for zone append so it does not cause late ENOSPC due to underreservation - mirror reading error messages show the mirror number - don't fallback to buffered IO for NOWAIT direct IO writes, we don't have the NOWAIT semantics for buffered io yet - send, fix sending link commands for existing file paths when there are deleted and created hardlinks for same files - repair all mirrors for profiles with more than 1 copy (raid1c34) - fix repair of compressed extents, unify where error detection and repair happen Core changes: - bio completion cleanups - don't double defer compression bios - simplify endio workqueues - add more data to btrfs_bio to avoid allocation for read requests - rework bio error handling so it's same what block layer does, the submission works and errors are consumed in endio - when asynchronous bio offload fails fall back to synchronous checksum calculation to avoid errors under writeback or memory pressure - new trace points - raid56 events - ordered extent operations - super block log_root_transid deprecated (never used) - mixed_backref and big_metadata sysfs feature files removed, they've been default for sufficiently long time, there are no known users and mixed_backref could be confused with mixed_groups Non-btrfs changes, API updates: - minor highmem API update to cover const arguments - switch all kmap/kmap_atomic to kmap_local - remove redundant flush_dcache_page() - address_space_operations::writepage callback removed - add bdev_max_segments() helper" * tag 'for-5.20-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux: (163 commits) btrfs: don't call btrfs_page_set_checked in finish_compressed_bio_read btrfs: fix repair of compressed extents btrfs: remove the start argument to check_data_csum and export btrfs: pass a btrfs_bio to btrfs_repair_one_sector btrfs: simplify the pending I/O counting in struct compressed_bio btrfs: repair all known bad mirrors btrfs: merge btrfs_dev_stat_print_on_error with its only caller btrfs: join running log transaction when logging new name btrfs: simplify error handling in btrfs_lookup_dentry btrfs: send: always use the rbtree based inode ref management infrastructure btrfs: send: fix sending link commands for existing file paths btrfs: send: introduce recorded_ref_alloc and recorded_ref_free btrfs: zoned: wait until zone is finished when allocation didn't progress btrfs: zoned: write out partially allocated region btrfs: zoned: activate necessary block group btrfs: zoned: activate metadata block group on flush_space btrfs: zoned: disable metadata overcommit for zoned btrfs: zoned: introduce space_info->active_total_bytes btrfs: zoned: finish least available block group on data bg allocation btrfs: let can_allocate_chunk return error ...

btrfs: raid56: transfer the bio counter reference to the raid submission helpers

2022-07-25T15:45:40+00:00

Transfer the bio counter reference acquired by btrfs_submit_bio to raid56_parity_write and raid56_parity_recovery together with the bio that the reference was acquired for instead of acquiring another reference in those helpers and dropping the original one in btrfs_submit_bio. Reviewed-by: Nikolay Borisov Tested-by: Nikolay Borisov Signed-off-by: Christoph Hellwig Signed-off-by: David Sterba

btrfs: do not return errors from raid56_parity_recover

2022-07-25T15:45:39+00:00

Always consume the bio and call the end_io handler on error instead of returning an error and letting the caller handle it. This matches what the block layer submission does and avoids any confusion on who needs to handle errors. Also use the proper bool type for the generic_io argument. Reviewed-by: Nikolay Borisov Tested-by: Nikolay Borisov Reviewed-by: Johannes Thumshirn Reviewed-by: Qu Wenruo Signed-off-by: Christoph Hellwig Signed-off-by: David Sterba

btrfs: do not return errors from raid56_parity_write

2022-07-25T15:45:39+00:00

Always consume the bio and call the end_io handler on error instead of returning an error and letting the caller handle it. This matches what the block layer submission does and avoids any confusion on who needs to handle errors. Reviewed-by: Nikolay Borisov Tested-by: Nikolay Borisov Reviewed-by: Qu Wenruo Reviewed-by: Johannes Thumshirn Signed-off-by: Christoph Hellwig Signed-off-by: David Sterba

btrfs: raid56: use fixed stripe length everywhere

2022-07-25T15:45:39+00:00

The raid56 code assumes a fixed stripe length BTRFS_STRIPE_LEN but there are functions passing it as arguments, this is not necessary. The fixed value has been used for a long time and though the stripe length should be configurable by super block member stripesize, this hasn't been implemented and would require more changes so we don't need to keep this code around until then. Partially based on a patch from Qu Wenruo. Reviewed-by: Nikolay Borisov Tested-by: Nikolay Borisov Reviewed-by: Johannes Thumshirn Reviewed-by: Qu Wenruo Signed-off-by: Christoph Hellwig [ update changelog ] Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: raid56: don't trust any cached sector in __raid56_parity_recover()

2022-07-25T15:45:37+00:00

[BUG] There is a small workload which will always fail with recent kernel: (A simplified version from btrfs/125 test case) mkfs.btrfs -f -m raid5 -d raid5 -b 1G $dev1 $dev2 $dev3 mount $dev1 $mnt xfs_io -f -c "pwrite -S 0xee 0 1M" $mnt/file1 sync umount $mnt btrfs dev scan -u $dev3 mount -o degraded $dev1 $mnt xfs_io -f -c "pwrite -S 0xff 0 128M" $mnt/file2 umount $mnt btrfs dev scan mount $dev1 $mnt btrfs balance start --full-balance $mnt umount $mnt The failure is always failed to read some tree blocks: BTRFS info (device dm-4): relocating block group 217710592 flags data|raid5 BTRFS error (device dm-4): parent transid verify failed on 38993920 wanted 9 found 7 BTRFS error (device dm-4): parent transid verify failed on 38993920 wanted 9 found 7 ... [CAUSE] With the recently added debug output, we can see all RAID56 operations related to full stripe 38928384: 56.1183: raid56_read_partial: full_stripe=38928384 devid=2 type=DATA1 offset=0 opf=0x0 physical=9502720 len=65536 56.1185: raid56_read_partial: full_stripe=38928384 devid=3 type=DATA2 offset=16384 opf=0x0 physical=9519104 len=16384 56.1185: raid56_read_partial: full_stripe=38928384 devid=3 type=DATA2 offset=49152 opf=0x0 physical=9551872 len=16384 56.1187: raid56_write_stripe: full_stripe=38928384 devid=3 type=DATA2 offset=0 opf=0x1 physical=9502720 len=16384 56.1188: raid56_write_stripe: full_stripe=38928384 devid=3 type=DATA2 offset=32768 opf=0x1 physical=9535488 len=16384 56.1188: raid56_write_stripe: full_stripe=38928384 devid=1 type=PQ1 offset=0 opf=0x1 physical=30474240 len=16384 56.1189: raid56_write_stripe: full_stripe=38928384 devid=1 type=PQ1 offset=32768 opf=0x1 physical=30507008 len=16384 56.1218: raid56_write_stripe: full_stripe=38928384 devid=3 type=DATA2 offset=49152 opf=0x1 physical=9551872 len=16384 56.1219: raid56_write_stripe: full_stripe=38928384 devid=1 type=PQ1 offset=49152 opf=0x1 physical=30523392 len=16384 56.2721: raid56_parity_recover: full stripe=38928384 eb=39010304 mirror=2 56.2723: raid56_parity_recover: full stripe=38928384 eb=39010304 mirror=2 56.2724: raid56_parity_recover: full stripe=38928384 eb=39010304 mirror=2 Before we enter raid56_parity_recover(), we have triggered some metadata write for the full stripe 38928384, this leads to us to read all the sectors from disk. Furthermore, btrfs raid56 write will cache its calculated P/Q sectors to avoid unnecessary read. This means, for that full stripe, after any partial write, we will have stale data, along with P/Q calculated using that stale data. Thankfully due to patch "btrfs: only write the sectors in the vertical stripe which has data stripes" we haven't submitted all the corrupted P/Q to disk. When we really need to recover certain range, aka in raid56_parity_recover(), we will use the cached rbio, along with its cached sectors (the full stripe is all cached). This explains why we have no event raid56_scrub_read_recover() triggered. Since we have the cached P/Q which is calculated using the stale data, the recovered one will just be stale. In our particular test case, it will always return the same incorrect metadata, thus causing the same error message "parent transid verify failed on 39010304 wanted 9 found 7" again and again. [BTRFS DESTRUCTIVE RMW PROBLEM] Test case btrfs/125 (and above workload) always has its trouble with the destructive read-modify-write (RMW) cycle: 0 32K 64K Data1: | Good | Good | Data2: | Bad | Bad | Parity: | Good | Good | In above case, if we trigger any write into Data1, we will use the bad data in Data2 to re-generate parity, killing the only chance to recovery Data2, thus Data2 is lost forever. This destructive RMW cycle is not specific to btrfs RAID56, but there are some btrfs specific behaviors making the case even worse: - Btrfs will cache sectors for unrelated vertical stripes. In above example, if we're only writing into 0~32K range, btrfs will still read data range (32K ~ 64K) of Data1, and (64K~128K) of Data2. This behavior is to cache sectors for later update. Incidentally commit d4e28d9b5f04 ("btrfs: raid56: make steal_rbio() subpage compatible") has a bug which makes RAID56 to never trust the cached sectors, thus slightly improve the situation for recovery. Unfortunately, follow up fix "btrfs: update stripe_sectors::uptodate in steal_rbio" will revert the behavior back to the old one. - Btrfs raid56 partial write will update all P/Q sectors and cache them This means, even if data at (64K ~ 96K) of Data2 is free space, and only (96K ~ 128K) of Data2 is really stale data. And we write into that (96K ~ 128K), we will update all the parity sectors for the full stripe. This unnecessary behavior will completely kill the chance of recovery. Thankfully, an unrelated optimization "btrfs: only write the sectors in the vertical stripe which has data stripes" will prevent submitting the write bio for untouched vertical sectors. That optimization will keep the on-disk P/Q untouched for a chance for later recovery. [FIX] Although we have no good way to completely fix the destructive RMW (unless we go full scrub for each partial write), we can still limit the damage. With patch "btrfs: only write the sectors in the vertical stripe which has data stripes" now we won't really submit the P/Q of unrelated vertical stripes, so the on-disk P/Q should still be fine. Now we really need to do is just drop all the cached sectors when doing recovery. By this, we have a chance to read the original P/Q from disk, and have a chance to recover the stale data, while still keep the cache to speed up regular write path. In fact, just dropping all the cache for recovery path is good enough to allow the test case btrfs/125 along with the small script to pass reliably. The lack of metadata write after the degraded mount, and forced metadata COW is saving us this time. So this patch will fix the behavior by not trust any cache in __raid56_parity_recover(), to solve the problem while still keep the cache useful. But please note that this test pass DOES NOT mean we have solved the destructive RMW problem, we just do better damage control a little better. Related patches: - btrfs: only write the sectors in the vertical stripe - d4e28d9b5f04 ("btrfs: raid56: make steal_rbio() subpage compatible") - btrfs: update stripe_sectors::uptodate in steal_rbio Signed-off-by: Qu Wenruo Signed-off-by: David Sterba

btrfs: use btrfs_raid_array to calculate number of parity stripes

2022-07-25T15:45:36+00:00

Use the raid table instead of hard coded values and rename the helper as it is exported. This could make later extension on RAID56 based profiles easier. Reviewed-by: Johannes Thumshirn Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: raid56: avoid double for loop inside raid56_parity_scrub_stripe()

2022-07-25T15:45:35+00:00

Originally it's iterating all the sectors which has dbitmap sector for the vertical stripe. It can be easily converted to sector bytenr iteration with an test_bit() call. Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: raid56: avoid double for loop inside raid56_rmw_stripe()

2022-07-25T15:45:35+00:00

This function doesn't even utilize full stripe skip, just iterate all the data sectors is definitely enough. Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba