--- /dev/null
+From foo@baz Tue Aug 23 09:23:04 AM CEST 2022
+From: Qu Wenruo <wqu@suse.com>
+Date: Sat, 20 Aug 2022 14:34:59 +0800
+Subject: btrfs: only write the sectors in the vertical stripe which has data stripes
+To: linux-btrfs@vger.kernel.org, stable@vger.kernel.org
+Cc: David Sterba <dsterba@suse.com>
+Message-ID: <f6ece031721b8d8beeb3e37cc320b8c424935463.1660977189.git.wqu@suse.com>
+
+From: Qu Wenruo <wqu@suse.com>
+
+commit bd8f7e627703ca5707833d623efcd43f104c7b3f upstream.
+
+If we have only 8K partial write at the beginning of a full RAID56
+stripe, we will write the following contents:
+
+ 0 8K 32K 64K
+Disk 1 (data): |XX| | |
+Disk 2 (data): | | |
+Disk 3 (parity): |XXXXXXXXXXXXXXX|XXXXXXXXXXXXXXX|
+
+|X| means the sector will be written back to disk.
+
+Note that, although we won't write any sectors from disk 2, but we will
+write the full 64KiB of parity to disk.
+
+This behavior is fine for now, but not for the future (especially for
+RAID56J, as we waste quite some space to journal the unused parity
+stripes).
+
+So here we will also utilize the btrfs_raid_bio::dbitmap, anytime we
+queue a higher level bio into an rbio, we will update rbio::dbitmap to
+indicate which vertical stripes we need to writeback.
+
+And at finish_rmw(), we also check dbitmap to see if we need to write
+any sector in the vertical stripe.
+
+So after the patch, above example will only lead to the following
+writeback pattern:
+
+ 0 8K 32K 64K
+Disk 1 (data): |XX| | |
+Disk 2 (data): | | |
+Disk 3 (parity): |XX| | |
+
+Acked-by: David Sterba <dsterba@suse.com>
+Signed-off-by: Qu Wenruo <wqu@suse.com>
+Signed-off-by: David Sterba <dsterba@suse.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ fs/btrfs/raid56.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++----
+ 1 file changed, 51 insertions(+), 4 deletions(-)
+
+--- a/fs/btrfs/raid56.c
++++ b/fs/btrfs/raid56.c
+@@ -334,6 +334,9 @@ static void merge_rbio(struct btrfs_raid
+ {
+ bio_list_merge(&dest->bio_list, &victim->bio_list);
+ dest->bio_list_bytes += victim->bio_list_bytes;
++ /* Also inherit the bitmaps from @victim. */
++ bitmap_or(dest->dbitmap, victim->dbitmap, dest->dbitmap,
++ dest->stripe_npages);
+ dest->generic_bio_cnt += victim->generic_bio_cnt;
+ bio_list_init(&victim->bio_list);
+ }
+@@ -878,6 +881,12 @@ static void rbio_orig_end_io(struct btrf
+
+ if (rbio->generic_bio_cnt)
+ btrfs_bio_counter_sub(rbio->fs_info, rbio->generic_bio_cnt);
++ /*
++ * Clear the data bitmap, as the rbio may be cached for later usage.
++ * do this before before unlock_stripe() so there will be no new bio
++ * for this bio.
++ */
++ bitmap_clear(rbio->dbitmap, 0, rbio->stripe_npages);
+
+ /*
+ * At this moment, rbio->bio_list is empty, however since rbio does not
+@@ -1212,6 +1221,9 @@ static noinline void finish_rmw(struct b
+ else
+ BUG();
+
++ /* We should have at least one data sector. */
++ ASSERT(bitmap_weight(rbio->dbitmap, rbio->stripe_npages));
++
+ /* at this point we either have a full stripe,
+ * or we've read the full stripe from the drive.
+ * recalculate the parity and write the new results.
+@@ -1285,6 +1297,11 @@ static noinline void finish_rmw(struct b
+ for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
+ for (pagenr = 0; pagenr < rbio->stripe_npages; pagenr++) {
+ struct page *page;
++
++ /* This vertical stripe has no data, skip it. */
++ if (!test_bit(pagenr, rbio->dbitmap))
++ continue;
++
+ if (stripe < rbio->nr_data) {
+ page = page_in_rbio(rbio, stripe, pagenr, 1);
+ if (!page)
+@@ -1309,6 +1326,11 @@ static noinline void finish_rmw(struct b
+
+ for (pagenr = 0; pagenr < rbio->stripe_npages; pagenr++) {
+ struct page *page;
++
++ /* This vertical stripe has no data, skip it. */
++ if (!test_bit(pagenr, rbio->dbitmap))
++ continue;
++
+ if (stripe < rbio->nr_data) {
+ page = page_in_rbio(rbio, stripe, pagenr, 1);
+ if (!page)
+@@ -1748,6 +1770,33 @@ static void btrfs_raid_unplug(struct blk
+ run_plug(plug);
+ }
+
++/* Add the original bio into rbio->bio_list, and update rbio::dbitmap. */
++static void rbio_add_bio(struct btrfs_raid_bio *rbio, struct bio *orig_bio)
++{
++ const struct btrfs_fs_info *fs_info = rbio->fs_info;
++ const u64 orig_logical = orig_bio->bi_iter.bi_sector << SECTOR_SHIFT;
++ const u64 full_stripe_start = rbio->bbio->raid_map[0];
++ const u32 orig_len = orig_bio->bi_iter.bi_size;
++ const u32 sectorsize = fs_info->sectorsize;
++ u64 cur_logical;
++
++ ASSERT(orig_logical >= full_stripe_start &&
++ orig_logical + orig_len <= full_stripe_start +
++ rbio->nr_data * rbio->stripe_len);
++
++ bio_list_add(&rbio->bio_list, orig_bio);
++ rbio->bio_list_bytes += orig_bio->bi_iter.bi_size;
++
++ /* Update the dbitmap. */
++ for (cur_logical = orig_logical; cur_logical < orig_logical + orig_len;
++ cur_logical += sectorsize) {
++ int bit = ((u32)(cur_logical - full_stripe_start) >>
++ PAGE_SHIFT) % rbio->stripe_npages;
++
++ set_bit(bit, rbio->dbitmap);
++ }
++}
++
+ /*
+ * our main entry point for writes from the rest of the FS.
+ */
+@@ -1764,9 +1813,8 @@ int raid56_parity_write(struct btrfs_fs_
+ btrfs_put_bbio(bbio);
+ return PTR_ERR(rbio);
+ }
+- bio_list_add(&rbio->bio_list, bio);
+- rbio->bio_list_bytes = bio->bi_iter.bi_size;
+ rbio->operation = BTRFS_RBIO_WRITE;
++ rbio_add_bio(rbio, bio);
+
+ btrfs_bio_counter_inc_noblocked(fs_info);
+ rbio->generic_bio_cnt = 1;
+@@ -2170,8 +2218,7 @@ int raid56_parity_recover(struct btrfs_f
+ }
+
+ rbio->operation = BTRFS_RBIO_READ_REBUILD;
+- bio_list_add(&rbio->bio_list, bio);
+- rbio->bio_list_bytes = bio->bi_iter.bi_size;
++ rbio_add_bio(rbio, bio);
+
+ rbio->faila = find_logical_bio_stripe(rbio, bio);
+ if (rbio->faila == -1) {
--- /dev/null
+From foo@baz Tue Aug 23 09:23:04 AM CEST 2022
+From: Qu Wenruo <wqu@suse.com>
+Date: Sat, 20 Aug 2022 14:35:00 +0800
+Subject: btrfs: raid56: don't trust any cached sector in __raid56_parity_recover()
+To: linux-btrfs@vger.kernel.org, stable@vger.kernel.org
+Cc: David Sterba <dsterba@suse.com>
+Message-ID: <f681096966272baafb5ef89183a851ab506a064f.1660977189.git.wqu@suse.com>
+
+From: Qu Wenruo <wqu@suse.com>
+
+commit f6065f8edeb25f4a9dfe0b446030ad995a84a088 upstream.
+
+[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
+
+Acked-by: David Sterba <dsterba@suse.com>
+Signed-off-by: Qu Wenruo <wqu@suse.com>
+Signed-off-by: David Sterba <dsterba@suse.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ fs/btrfs/raid56.c | 19 ++++++-------------
+ 1 file changed, 6 insertions(+), 13 deletions(-)
+
+--- a/fs/btrfs/raid56.c
++++ b/fs/btrfs/raid56.c
+@@ -2116,9 +2116,12 @@ static int __raid56_parity_recover(struc
+ atomic_set(&rbio->error, 0);
+
+ /*
+- * read everything that hasn't failed. Thanks to the
+- * stripe cache, it is possible that some or all of these
+- * pages are going to be uptodate.
++ * Read everything that hasn't failed. However this time we will
++ * not trust any cached sector.
++ * As we may read out some stale data but higher layer is not reading
++ * that stale part.
++ *
++ * So here we always re-read everything in recovery path.
+ */
+ for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
+ if (rbio->faila == stripe || rbio->failb == stripe) {
+@@ -2127,16 +2130,6 @@ static int __raid56_parity_recover(struc
+ }
+
+ for (pagenr = 0; pagenr < rbio->stripe_npages; pagenr++) {
+- struct page *p;
+-
+- /*
+- * the rmw code may have already read this
+- * page in
+- */
+- p = rbio_stripe_page(rbio, stripe, pagenr);
+- if (PageUptodate(p))
+- continue;
+-
+ ret = rbio_add_io_page(rbio, &bio_list,
+ rbio_stripe_page(rbio, stripe, pagenr),
+ stripe, pagenr, rbio->stripe_len);
projects / thirdparty / kernel / stable-queue.git / commitdiff
