[PATCH v4 00/10] btrfs: error handling fixes

[PATCH v4 00/10] btrfs: error handling fixes

[Qu Wenruo]

[CHANGELOG]
v4:
- Rebased to the latest for-next branch
  This involves several minor conflicts due to the recent cleanup.

- Minor comment/commit message update

- Use btrfs_root_id() for error messages

- Fix the double accounting error reintroduced in the last patch
  Where the run_delalloc_nocow() function has a very weird handling for
  COW fallback, where @cur_offset can either be @cow_start or @cow_end
  depending on the fallback_to_cow() entrance.

v3:
- Add a new patch to move the ordered extent cleanup into
  cow_file_range() and run_delalloc_nocow()

- Update the comment of writepage_dealloc()
  To give a more detailed view on what should be done for all the 3
  return value patterns

- Rename the variable @last_finished to @last_finished_delalloc_end
  And enhance the comment of it.

- Add a comment on why we want submit_one_bio() after
  submit_one_sector() failed

- Add a comment explaining what cleanup_dirty_folios() does

- Update the ASCII graph to use @cur_offset other than @cur_start

v2:
- Fix the btrfs_cleanup_ordered_extents() call inside
  btrfs_run_delalloc_range()

  Since we no longer call btrfs_mark_ordered_io_finished() if
  btrfs_run_delalloc_range() failed, the existing
  btrfs_cleanup_ordered_extents() call with @locked_folio will cause the
  subpage range not to be properly cleaned up.

  This can lead to hanging ordered extents for subpage cases.

- Update the commit message of the first patch
  With more detailed analyse on how the double accounting happens.
  It's pretty complex and very lengthy, but is easier to understand (as
  least I hope so).

  The root cause is the btrfs_cleanup_ordered_extents()'s range split
  behavior, which is not subpage compatible and is cursed in the first
  place.

  So the fix is still the same, by removing the split OE handling
  completely.

- A new patch to cleanup the @locked_folio parameter of
  btrfs_cleanup_ordered_extents()

I believe there is a regression in the last 2 or 3 releases where
metadata/data space reservation code is no longer working properly,
result us to hit -ENOSPC during btrfs_run_delalloc_range().

One of the most common situation to hit such problem is during
generic/750, along with other long running generic tests.

Although I should start bisecting the space reservation bug, but I can
not help but fixing the exposed bugs first.

This exposed quite some long existing bugs, all in the error handling
paths, that can lead to the following crashes

- Double ordered extent accounting
  Triggers WARN_ON_OCE() inside can_finish_ordered_extent() then crash.

  This bug is fixed by the first 3 patches.
  The first patch is the most important one, since it's pretty easy to
  trigger in the real world, and very long existing.

  The second patch is just a precautious fix, not easy to happen in the
  real world.

  The third one is also possible in the real world, but only possible
  with the recently enabled subpage compression write support.

- Subpage ASSERT() triggered, where subpage folio bitmap differs from
  folio status
  This happens most likey in submit_uncompressed_range(), where it
  unlock the folio without updating the subpage bitmaps.

  This bug is fixed by the 3rd patch.

- WARN_ON() if out-of-tree patch "btrfs: reject out-of-band dirty folios
  during writeback" applied
  This is a more complex case, where error handling leaves some folios
  dirty, but with EXTENT_DELALLOC flag cleared from extent io tree.

  Such dirty folios are still possible to be written back later, but
  since there is no EXTENT_DELALLOC flag, it will be treat as
  out-of-band dirty flags and trigger COW fixup.

  This bug is fixed by the 4th and 5th patch

With so many existing bugs exposed, there is more than enough motivation
to make btrfs_run_delalloc_range() (and its delalloc range functions)
output extra error messages so that at least we know something is wrong.

And those error messages have already helped a lot during my
development.

Patches 6~8 are here to enhance the error messages.

Patch 9 is to cleanup the unnecessary @locked_folio parameter
of btrfs_cleanup_ordered_extents().

The final one is to make ordered extent cleanup to be more sane,
following the common reclaim-asap principle, other than delay the
cleanup until btrfs_run_delalloc_range().

With all these patches applied, at least fstests can finish reliably,
otherwise it frequently crashes in generic tests that I was unable to
finish even one full run since the space reservation regression.

Qu Wenruo (10):
  btrfs: fix double accounting race when btrfs_run_delalloc_range()
    failed
  btrfs: fix double accounting race when extent_writepage_io() failed
  btrfs: fix the error handling of submit_uncompressed_range()
  btrfs: do proper folio cleanup when cow_file_range() failed
  btrfs: do proper folio cleanup when run_delalloc_nocow() failed
  btrfs: subpage: fix the bitmap dump for the locked flags
  btrfs: subpage: dump the involved bitmap when ASSERT() failed
  btrfs: add extra error messages for delalloc range related errors
  btrfs: remove the unused @locked_folio parameter from
    btrfs_cleanup_ordered_extents()
  btrfs: move ordered extent cleanup to where they are allocated

 fs/btrfs/extent_io.c | 104 ++++++++++++----
 fs/btrfs/inode.c     | 279 ++++++++++++++++++++++++++-----------------
 fs/btrfs/subpage.c   |  47 ++++++--
 fs/btrfs/subpage.h   |  13 ++
 4 files changed, 300 insertions(+), 143 deletions(-)

-- 
2.47.1

[PATCH v4 01/10] btrfs: fix double accounting race when btrfs_run_delalloc_range() failed

[Qu Wenruo]

[BUG]
When running btrfs with block size (4K) smaller than page size (64K,
aarch64), there is a very high chance to crash the kernel at
generic/750, with the following messages:
(before the call traces, there are 3 extra debug messages added)

 BTRFS warning (device dm-3): read-write for sector size 4096 with page size 65536 is experimental
 BTRFS info (device dm-3): checking UUID tree
 hrtimer: interrupt took 5451385 ns
 BTRFS error (device dm-3): cow_file_range failed, root=4957 inode=257 start=1605632 len=69632: -28
 BTRFS error (device dm-3): run_delalloc_nocow failed, root=4957 inode=257 start=1605632 len=69632: -28
 BTRFS error (device dm-3): failed to run delalloc range, root=4957 ino=257 folio=1572864 submit_bitmap=8-15 start=1605632 len=69632: -28
 ------------[ cut here ]------------
 WARNING: CPU: 2 PID: 3020984 at ordered-data.c:360 can_finish_ordered_extent+0x370/0x3b8 [btrfs]
 CPU: 2 UID: 0 PID: 3020984 Comm: kworker/u24:1 Tainted: G           OE      6.13.0-rc1-custom+ #89
 Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
 Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
 Workqueue: events_unbound btrfs_async_reclaim_data_space [btrfs]
 pc : can_finish_ordered_extent+0x370/0x3b8 [btrfs]
 lr : can_finish_ordered_extent+0x1ec/0x3b8 [btrfs]
 Call trace:
  can_finish_ordered_extent+0x370/0x3b8 [btrfs] (P)
  can_finish_ordered_extent+0x1ec/0x3b8 [btrfs] (L)
  btrfs_mark_ordered_io_finished+0x130/0x2b8 [btrfs]
  extent_writepage+0x10c/0x3b8 [btrfs]
  extent_write_cache_pages+0x21c/0x4e8 [btrfs]
  btrfs_writepages+0x94/0x160 [btrfs]
  do_writepages+0x74/0x190
  filemap_fdatawrite_wbc+0x74/0xa0
  start_delalloc_inodes+0x17c/0x3b0 [btrfs]
  btrfs_start_delalloc_roots+0x17c/0x288 [btrfs]
  shrink_delalloc+0x11c/0x280 [btrfs]
  flush_space+0x288/0x328 [btrfs]
  btrfs_async_reclaim_data_space+0x180/0x228 [btrfs]
  process_one_work+0x228/0x680
  worker_thread+0x1bc/0x360
  kthread+0x100/0x118
  ret_from_fork+0x10/0x20
 ---[ end trace 0000000000000000 ]---
 BTRFS critical (device dm-3): bad ordered extent accounting, root=4957 ino=257 OE offset=1605632 OE len=16384 to_dec=16384 left=0
 BTRFS critical (device dm-3): bad ordered extent accounting, root=4957 ino=257 OE offset=1622016 OE len=12288 to_dec=12288 left=0
 Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
 BTRFS critical (device dm-3): bad ordered extent accounting, root=4957 ino=257 OE offset=1634304 OE len=8192 to_dec=4096 left=0
 CPU: 1 UID: 0 PID: 3286940 Comm: kworker/u24:3 Tainted: G        W  OE      6.13.0-rc1-custom+ #89
 Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
 Workqueue:  btrfs_work_helper [btrfs] (btrfs-endio-write)
 pstate: 404000c5 (nZcv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : process_one_work+0x110/0x680
 lr : worker_thread+0x1bc/0x360
 Call trace:
  process_one_work+0x110/0x680 (P)
  worker_thread+0x1bc/0x360 (L)
  worker_thread+0x1bc/0x360
  kthread+0x100/0x118
  ret_from_fork+0x10/0x20
 Code: f84086a1 f9000fe1 53041c21 b9003361 (f9400661)
 ---[ end trace 0000000000000000 ]---
 Kernel panic - not syncing: Oops: Fatal exception
 SMP: stopping secondary CPUs
 SMP: failed to stop secondary CPUs 2-3
 Dumping ftrace buffer:
    (ftrace buffer empty)
 Kernel Offset: 0x275bb9540000 from 0xffff800080000000
 PHYS_OFFSET: 0xffff8fbba0000000
 CPU features: 0x100,00000070,00801250,8201720b

[CAUSE]
The above warning is triggered immediately after the delalloc range
failure, this happens in the following sequence:

- Range [1568K, 1636K) is dirty

   1536K  1568K     1600K    1636K  1664K
   |      |/////////|////////|      |

  Where 1536K, 1600K and 1664K are page boundaries (64K page size)

- Enter extent_writepage() for page 1536K

- Enter run_delalloc_nocow() with locked page 1536K and range
  [1568K, 1636K)
  This is due to the inode has preallocated extents.

- Enter cow_file_range() with locked page 1536K and range
  [1568K, 1636K)

- btrfs_reserve_extent() only reserved two extents
  The main loop of cow_file_range() only reserved two data extents,

  Now we have:

   1536K  1568K        1600K    1636K  1664K
   |      |<-->|<--->|/|///////|      |
               1584K  1596K
  Range [1568K, 1596K) has ordered extent reserved.

- btrfs_reserve_extent() failed inside cow_file_range() for file offset
  1596K
  This is already a bug in our space reservation code, but for now let's
  focus on the error handling path.

  Now cow_file_range() returned -ENOSPC.

- btrfs_run_delalloc_range() do error cleanup <<< ROOT CAUSE
  Call btrfs_cleanup_ordered_extents() with locked folio 1536K and range
  [1568K, 1636K)

  Function btrfs_cleanup_ordered_extents() normally needs to skip the
  ranges inside the folio, as it will normally be cleaned up by
  extent_writepage().

  Such split error handling is already problematic in the first place.

  What's worse is the folio range skipping itself, which is not taking
  subpage cases into consideration at all, it will only skip the range
  if the page start >= the range start.
  In our case, the page start < the range start, since for subpage cases
  we can have delalloc ranges inside the folio but not covering the
  folio.

  So it doesn't skip the page range at all.
  This means all the ordered extents, both [1568K, 1584K) and
  [1584K, 1596K) will be marked as IOERR.

  And those two ordered extents have no more pending ios, it is marked
  finished, and *QUEUED* to be deleted from the io tree.

- extent_writepage() do error cleanup
  Call btrfs_mark_ordered_io_finished() for the range [1536K, 1600K).

  Although ranges [1568K, 1584K) and [1584K, 1596K) are finished, the
  deletion from io tree is async, it may or may not happen at this
  timing.

  If the ranges are not yet removed, we will do double cleaning on those
  ranges, triggers the above ordered extent warnings.

In theory there are other bugs, like the cleanup in extent_writepage()
can cause double accounting on ranges that are submitted async
(compression for example).

But that's much harder to trigger because normally we do not mix regular
and compression delalloc ranges.

[FIX]
The folio range split is already buggy and not subpage compatible, it's
introduced a long time ago where subpage support is not even considered.

So instead of splitting the ordered extents cleanup into the folio range
and out of folio range, do all the cleanup inside writepage_delalloc().

- Pass @NULL as locked_folio for btrfs_cleanup_ordered_extents() in
  btrfs_run_delalloc_range()

- Skip the btrfs_cleanup_ordered_extents() if writepage_delalloc()
  failed

  So all ordered extents are only cleaned up by
  btrfs_run_delalloc_range().

- Handle the ranges that already have ordered extents allocated
  If part of the folio already has ordered extent allocated, and
  btrfs_run_delalloc_range() failed, we also need to cleanup that range.

Now we have a concentrated error handling for ordered extents during
btrfs_run_delalloc_range().

Cc: stable@vger.kernel.org # 5.15+
Fixes: d1051d6ebf8e ("btrfs: Fix error handling in btrfs_cleanup_ordered_extents")
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 57 ++++++++++++++++++++++++++++++++++++--------
 fs/btrfs/inode.c     |  2 +-
 2 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index c068a442753c..7aa3d8c2b0c3 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1136,12 +1136,17 @@ static bool find_next_delalloc_bitmap(struct folio *folio,
 /*
  * helper for extent_writepage(), doing all of the delayed allocation setup.
  *
- * This returns 1 if btrfs_run_delalloc_range function did all the work required
- * to write the page (copy into inline extent).  In this case the IO has
- * been started and the page is already unlocked.
+ * Return >0 if all the dirty blocks are submitted async (compression) or inlined.
+ * The @folio should no longer be touched (treat it as already unlocked).
  *
- * This returns 0 if all went well (page still locked)
- * This returns < 0 if there were errors (page still locked)
+ * Return 0 if there is still dirty block that needs to be submitted through
+ * extent_writepage_io().
+ * bio_ctrl->submit_bitmap will indicate which blocks of the folio should be
+ * submitted, and @folio is still kept locked.
+ *
+ * Return <0 if there is any error hit.
+ * Any allocated ordered extent range covering this folio will be marked
+ * finished (IOERR), and @folio is still kept locked.
  */
 static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 						 struct folio *folio,
@@ -1159,6 +1164,16 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 	 * last delalloc end.
 	 */
 	u64 last_delalloc_end = 0;
+	/*
+	 * The range end (exclusive) of the last successfully finished delalloc
+	 * range.
+	 * Any range covered by ordered extent must either be manually marked
+	 * finished (error handling), or has IO submitted (and finish the
+	 * ordered extent normally).
+	 *
+	 * This records the end of ordered extent cleanup if we hit an error.
+	 */
+	u64 last_finished_delalloc_end = page_start;
 	u64 delalloc_start = page_start;
 	u64 delalloc_end = page_end;
 	u64 delalloc_to_write = 0;
@@ -1227,11 +1242,19 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 			found_len = last_delalloc_end + 1 - found_start;
 
 		if (ret >= 0) {
+			/*
+			 * Some delalloc range may be created by previous folios.
+			 * Thus we still need to clean those range up during error
+			 * handling.
+			 */
+			last_finished_delalloc_end = found_start;
 			/* No errors hit so far, run the current delalloc range. */
 			ret = btrfs_run_delalloc_range(inode, folio,
 						       found_start,
 						       found_start + found_len - 1,
 						       wbc);
+			if (ret >= 0)
+				last_finished_delalloc_end = found_start + found_len;
 		} else {
 			/*
 			 * We've hit an error during previous delalloc range,
@@ -1266,8 +1289,22 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 
 		delalloc_start = found_start + found_len;
 	}
-	if (ret < 0)
+	/*
+	 * It's possible we have some ordered extents created before we hit
+	 * an error, cleanup non-async successfully created delalloc ranges.
+	 */
+	if (unlikely(ret < 0)) {
+		unsigned int bitmap_size = min(
+			(last_finished_delalloc_end - page_start) >>
+			fs_info->sectorsize_bits,
+			fs_info->sectors_per_page);
+
+		for_each_set_bit(bit, &bio_ctrl->submit_bitmap, bitmap_size)
+			btrfs_mark_ordered_io_finished(inode, folio,
+				page_start + (bit << fs_info->sectorsize_bits),
+				fs_info->sectorsize, false);
 		return ret;
+	}
 out:
 	if (last_delalloc_end)
 		delalloc_end = last_delalloc_end;
@@ -1501,13 +1538,13 @@ static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl
 
 	bio_ctrl->wbc->nr_to_write--;
 
-done:
-	if (ret) {
+	if (ret)
 		btrfs_mark_ordered_io_finished(inode, folio,
 					       page_start, PAGE_SIZE, !ret);
-		mapping_set_error(folio->mapping, ret);
-	}
 
+done:
+	if (ret < 0)
+		mapping_set_error(folio->mapping, ret);
 	/*
 	 * Only unlock ranges that are submitted. As there can be some async
 	 * submitted ranges inside the folio.
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1546f341f9a4..85e36dbe1e1f 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2301,7 +2301,7 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct folio *locked_fol
 
 out:
 	if (ret < 0)
-		btrfs_cleanup_ordered_extents(inode, locked_folio, start,
+		btrfs_cleanup_ordered_extents(inode, NULL, start,
 					      end - start + 1);
 	return ret;
 }
-- 
2.47.1

[PATCH v4 02/10] btrfs: fix double accounting race when extent_writepage_io() failed

[Qu Wenruo]

[BUG]
If submit_one_sector() failed inside extent_writepage_io() for sector
size < page size cases (e.g. 4K sector size and 64K page size), then
we can hit double ordered extent accounting error.

This should be very rare, as submit_one_sector() only fails when we
failed to grab the extent map, and such extent map should exist inside
the memory and have been pinned.

[CAUSE]
For example we have the following folio layout:

    0  4K          32K    48K   60K 64K
    |//|           |//////|     |///|

Where |///| is the dirty range we need to writeback. The 3 different
dirty ranges are submitted for regular COW.

Now we hit the following sequence:

- submit_one_sector() returned 0 for [0, 4K)

- submit_one_sector() returned 0 for [32K, 48K)

- submit_one_sector() returned error for [60K, 64K)

- btrfs_mark_ordered_io_finished() called for the whole folio
  This will mark the following ranges as finished:
  * [0, 4K)
  * [32K, 48K)
    Both ranges have their IO already submitted, this cleanup will
    lead to double accounting.

  * [60K, 64K)
    That's the correct cleanup.

The only good news is, this error is only theoretical, as the target
extent map is always pinned, thus we should directly grab it from
memory, other than reading it from the disk.

[FIX]
Instead of calling btrfs_mark_ordered_io_finished() for the whole folio
range, which can touch ranges we should not touch, instead
move the error handling inside extent_writepage_io().

So that we can cleanup exact sectors that are ought to be submitted but
failed.

This provide much more accurate cleanup, avoiding the double accounting.

Cc: stable@vger.kernel.org # 5.15+
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 7aa3d8c2b0c3..f50e4fccd909 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1420,6 +1420,7 @@ static noinline_for_stack int extent_writepage_io(struct btrfs_inode *inode,
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
 	unsigned long range_bitmap = 0;
 	bool submitted_io = false;
+	bool error = false;
 	const u64 folio_start = folio_pos(folio);
 	u64 cur;
 	int bit;
@@ -1462,11 +1463,26 @@ static noinline_for_stack int extent_writepage_io(struct btrfs_inode *inode,
 			break;
 		}
 		ret = submit_one_sector(inode, folio, cur, bio_ctrl, i_size);
-		if (ret < 0)
-			goto out;
+		if (unlikely(ret < 0)) {
+			/*
+			 * bio_ctrl may contain a bio crossing several folios.
+			 * Submit it immediately so that the bio has a chance
+			 * to finish normally, other than marked as error.
+			 */
+			submit_one_bio(bio_ctrl);
+			/*
+			 * Failed to grab the extent map which should be very rare.
+			 * Since there is no bio submitted to finish the ordered
+			 * extent, we have to manually finish this sector.
+			 */
+			btrfs_mark_ordered_io_finished(inode, folio, cur,
+					fs_info->sectorsize, false);
+			error = true;
+			continue;
+		}
 		submitted_io = true;
 	}
-out:
+
 	/*
 	 * If we didn't submitted any sector (>= i_size), folio dirty get
 	 * cleared but PAGECACHE_TAG_DIRTY is not cleared (only cleared
@@ -1474,8 +1490,11 @@ static noinline_for_stack int extent_writepage_io(struct btrfs_inode *inode,
 	 *
 	 * Here we set writeback and clear for the range. If the full folio
 	 * is no longer dirty then we clear the PAGECACHE_TAG_DIRTY tag.
+	 *
+	 * If we hit any error, the corresponding sector will still be dirty
+	 * thus no need to clear PAGECACHE_TAG_DIRTY.
 	 */
-	if (!submitted_io) {
+	if (!submitted_io && !error) {
 		btrfs_folio_set_writeback(fs_info, folio, start, len);
 		btrfs_folio_clear_writeback(fs_info, folio, start, len);
 	}
@@ -1495,7 +1514,6 @@ static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl
 {
 	struct btrfs_inode *inode = BTRFS_I(folio->mapping->host);
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
-	const u64 page_start = folio_pos(folio);
 	int ret;
 	size_t pg_offset;
 	loff_t i_size = i_size_read(&inode->vfs_inode);
@@ -1538,10 +1556,6 @@ static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl
 
 	bio_ctrl->wbc->nr_to_write--;
 
-	if (ret)
-		btrfs_mark_ordered_io_finished(inode, folio,
-					       page_start, PAGE_SIZE, !ret);
-
 done:
 	if (ret < 0)
 		mapping_set_error(folio->mapping, ret);
@@ -2314,11 +2328,8 @@ void extent_write_locked_range(struct inode *inode, const struct folio *locked_f
 		if (ret == 1)
 			goto next_page;
 
-		if (ret) {
-			btrfs_mark_ordered_io_finished(BTRFS_I(inode), folio,
-						       cur, cur_len, !ret);
+		if (ret)
 			mapping_set_error(mapping, ret);
-		}
 		btrfs_folio_end_lock(fs_info, folio, cur, cur_len);
 		if (ret < 0)
 			found_error = true;
-- 
2.47.1

[PATCH v4 03/10] btrfs: fix the error handling of submit_uncompressed_range()

[Qu Wenruo]

[BUG]
If btrfs failed to compress the range, or can not reserve a large enough
data extent (e.g. too fragmented free space), btrfs will fall back to
submit_uncompressed_range().

But inside submit_uncompressed_range(), run_dealloc_cow() can also fail
due to -ENOSPC or whatever other errors.

In that case there are 3 bugs in the error handling:

1) Double freeing for the same ordered extent
   Which can lead to crash due to ordered extent double accounting

2) Start/end writeback without updating the subpage writeback bitmap

3) Unlock the folio without clear the subpage lock bitmap

Both bug 2) and 3) will crash the kernel if the btrfs block size is
smaller than folio size, as the next time the folio get writeback/lock
updates, subpage will find the bitmap already have the range set,
triggering an ASSERT().

[CAUSE]
Bug 1) happens in the following call chain:

  submit_uncompressed_range()
  |- run_dealloc_cow()
  |  |- cow_file_range()
  |     |- btrfs_reserve_extent()
  |        Failed with -ENOSPC or whatever error
  |
  |- btrfs_clean_up_ordered_extents()
  |  |- btrfs_mark_ordered_io_finished()
  |     Which cleans all the ordered extents in the async_extent range.
  |
  |- btrfs_mark_ordered_io_finished()
     Which cleans the folio range.

The finished ordered extents may not be immediately removed from the
ordered io tree, as they are removed inside a work queue.

So the second btrfs_mark_ordered_io_finished() may find the finished but
not-yet-removed ordered extents, and double free them.

Furthermore, the second btrfs_mark_ordered_io_finished() is not subpage
compatible, as it uses fixed folio_pos() with PAGE_SIZE, which can cover
other ordered extents.

Bug 2) and 3) are more straight forward, btrfs just calls folio_unlock(),
folio_start_writeback() and folio_end_writeback(), other than the helpers
which handle subpage cases.

[FIX]
For bug 1) since the first btrfs_cleanup_ordered_extents() call is
handling the whole range, we should not do the second
btrfs_mark_ordered_io_finished() call.

And for the first btrfs_cleanup_ordered_extents(), we no longer need to
pass the @locked_page parameter, as we are already in the async extent
context, thus will never rely on the error handling inside
btrfs_run_delalloc_range().

So just let the btrfs_clean_up_ordered_extents() to handle every folio
equally.

For bug 2) we should not even call
folio_start_writeback()/folio_end_writeback() anymore.
As the error handling protocol, cow_file_range() should clear
dirty flag and start/finish the writeback for the whole range passed in.

For bug 3) just change the folio_unlock() to btrfs_folio_end_lock()
helper.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c | 16 ++++------------
 1 file changed, 4 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 85e36dbe1e1f..c23993cb7bdc 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1128,19 +1128,11 @@ static void submit_uncompressed_range(struct btrfs_inode *inode,
 			       &wbc, false);
 	wbc_detach_inode(&wbc);
 	if (ret < 0) {
-		btrfs_cleanup_ordered_extents(inode, locked_folio,
+		btrfs_cleanup_ordered_extents(inode, NULL,
 					      start, end - start + 1);
-		if (locked_folio) {
-			const u64 page_start = folio_pos(locked_folio);
-
-			folio_start_writeback(locked_folio);
-			folio_end_writeback(locked_folio);
-			btrfs_mark_ordered_io_finished(inode, locked_folio,
-						       page_start, PAGE_SIZE,
-						       !ret);
-			mapping_set_error(locked_folio->mapping, ret);
-			folio_unlock(locked_folio);
-		}
+		if (locked_folio)
+			btrfs_folio_end_lock(inode->root->fs_info, locked_folio,
+					     start, async_extent->ram_size);
 	}
 }
 
-- 
2.47.1

[PATCH v4 04/10] btrfs: do proper folio cleanup when cow_file_range() failed

[Qu Wenruo]

[BUG]
When testing with COW fixup marked as BUG_ON() (this is involved with the
new pin_user_pages*() change, which should not result new out-of-band
dirty pages), I hit a crash triggered by the BUG_ON() from hitting COW
fixup path.

This BUG_ON() happens just after a failed btrfs_run_delalloc_range():

 BTRFS error (device dm-2): failed to run delalloc range, root 348 ino 405 folio 65536 submit_bitmap 6-15 start 90112 len 106496: -28
 ------------[ cut here ]------------
 kernel BUG at fs/btrfs/extent_io.c:1444!
 Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
 CPU: 0 UID: 0 PID: 434621 Comm: kworker/u24:8 Tainted: G           OE      6.12.0-rc7-custom+ #86
 Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
 Workqueue: events_unbound btrfs_async_reclaim_data_space [btrfs]
 pc : extent_writepage_io+0x2d4/0x308 [btrfs]
 lr : extent_writepage_io+0x2d4/0x308 [btrfs]
 Call trace:
  extent_writepage_io+0x2d4/0x308 [btrfs]
  extent_writepage+0x218/0x330 [btrfs]
  extent_write_cache_pages+0x1d4/0x4b0 [btrfs]
  btrfs_writepages+0x94/0x150 [btrfs]
  do_writepages+0x74/0x190
  filemap_fdatawrite_wbc+0x88/0xc8
  start_delalloc_inodes+0x180/0x3b0 [btrfs]
  btrfs_start_delalloc_roots+0x174/0x280 [btrfs]
  shrink_delalloc+0x114/0x280 [btrfs]
  flush_space+0x250/0x2f8 [btrfs]
  btrfs_async_reclaim_data_space+0x180/0x228 [btrfs]
  process_one_work+0x164/0x408
  worker_thread+0x25c/0x388
  kthread+0x100/0x118
  ret_from_fork+0x10/0x20
 Code: aa1403e1 9402f3ef aa1403e0 9402f36f (d4210000)
 ---[ end trace 0000000000000000 ]---

[CAUSE]
That failure is mostly from cow_file_range(), where we can hit -ENOSPC.

Although the -ENOSPC is already a bug related to our space reservation
code, let's just focus on the error handling.

For example, we have the following dirty range [0, 64K) of an inode,
with 4K sector size and 4K page size:

   0        16K        32K       48K       64K
   |///////////////////////////////////////|
   |#######################################|

Where |///| means page are still dirty, and |###| means the extent io
tree has EXTENT_DELALLOC flag.

- Enter extent_writepage() for page 0

- Enter btrfs_run_delalloc_range() for range [0, 64K)

- Enter cow_file_range() for range [0, 64K)

- Function btrfs_reserve_extent() only reserved one 16K extent
  So we created extent map and ordered extent for range [0, 16K)

   0        16K        32K       48K       64K
   |////////|//////////////////////////////|
   |<- OE ->|##############################|

   And range [0, 16K) has its delalloc flag cleared.
   But since we haven't yet submit any bio, involved 4 pages are still
   dirty.

- Function btrfs_reserve_extent() return with -ENOSPC
  Now we have to run error cleanup, which will clear all
  EXTENT_DELALLOC* flags and clear the dirty flags for the remaining
  ranges:

   0        16K        32K       48K       64K
   |////////|                              |
   |        |                              |

  Note that range [0, 16K) still has their pages dirty.

- Some time later, writeback are triggered again for the range [0, 16K)
  since the page range still have dirty flags.

- btrfs_run_delalloc_range() will do nothing because there is no
  EXTENT_DELALLOC flag.

- extent_writepage_io() find page 0 has no ordered flag
  Which falls into the COW fixup path, triggering the BUG_ON().

Unfortunately this error handling bug dates back to the introduction of btrfs.
Thankfully with the abuse of cow fixup, at least it won't crash the
kernel.

[FIX]
Instead of immediately unlock the extent and folios, we keep the extent
and folios locked until either erroring out or the whole delalloc range
finished.

When the whole delalloc range finished without error, we just unlock the
whole range with PAGE_SET_ORDERED (and PAGE_UNLOCK for !keep_locked
cases), with EXTENT_DELALLOC and EXTENT_LOCKED cleared.
And those involved folios will be properly submitted, with their dirty
flags cleared during submission.

For the error path, it will be a little more complex:

- The range with ordered extent allocated (range (1))
  We only clear the EXTENT_DELALLOC and EXTENT_LOCKED, as the remaining
  flags are cleaned up by
  btrfs_mark_ordered_io_finished()->btrfs_finish_one_ordered().

  For folios we finish the IO (clear dirty, start writeback and
  immediately finish the writeback) and unlock the folios.

- The range with reserved extent but no ordered extent (range(2))
- The range we never touched (range(3))
  For both range (2) and range(3) the behavior is not changed.

Now even if cow_file_range() failed halfway with some successfully
reserved extents/ordered extents, we will keep all folios clean, so
there will be no future writeback triggered on them.

Cc: stable@vger.kernel.org
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c | 65 ++++++++++++++++++++++++------------------------
 1 file changed, 32 insertions(+), 33 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c23993cb7bdc..b94c4abcda3a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1363,6 +1363,17 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 
 	alloc_hint = btrfs_get_extent_allocation_hint(inode, start, num_bytes);
 
+	/*
+	 * We're not doing compressed IO, don't unlock the first page
+	 * (which the caller expects to stay locked), don't clear any
+	 * dirty bits and don't set any writeback bits
+	 *
+	 * Do set the Ordered (Private2) bit so we know this page was
+	 * properly setup for writepage.
+	 */
+	page_ops = (keep_locked ? 0 : PAGE_UNLOCK);
+	page_ops |= PAGE_SET_ORDERED;
+
 	/*
 	 * Relocation relies on the relocated extents to have exactly the same
 	 * size as the original extents. Normally writeback for relocation data
@@ -1422,6 +1433,10 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 		file_extent.offset = 0;
 		file_extent.compression = BTRFS_COMPRESS_NONE;
 
+		/*
+		 * Locked range will be released either during error clean up or
+		 * after the whole range is finished.
+		 */
 		lock_extent(&inode->io_tree, start, start + cur_alloc_size - 1,
 			    &cached);
 
@@ -1467,21 +1482,6 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 
 		btrfs_dec_block_group_reservations(fs_info, ins.objectid);
 
-		/*
-		 * We're not doing compressed IO, don't unlock the first page
-		 * (which the caller expects to stay locked), don't clear any
-		 * dirty bits and don't set any writeback bits
-		 *
-		 * Do set the Ordered flag so we know this page was
-		 * properly setup for writepage.
-		 */
-		page_ops = (keep_locked ? 0 : PAGE_UNLOCK);
-		page_ops |= PAGE_SET_ORDERED;
-
-		extent_clear_unlock_delalloc(inode, start, start + cur_alloc_size - 1,
-					     locked_folio, &cached,
-					     EXTENT_LOCKED | EXTENT_DELALLOC,
-					     page_ops);
 		if (num_bytes < cur_alloc_size)
 			num_bytes = 0;
 		else
@@ -1498,6 +1498,9 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 		if (ret)
 			goto out_unlock;
 	}
+	extent_clear_unlock_delalloc(inode, orig_start, end, locked_folio, &cached,
+				     EXTENT_LOCKED | EXTENT_DELALLOC,
+				     page_ops);
 done:
 	if (done_offset)
 		*done_offset = end;
@@ -1518,35 +1521,31 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 	 * We process each region below.
 	 */
 
-	clear_bits = EXTENT_LOCKED | EXTENT_DELALLOC | EXTENT_DELALLOC_NEW |
-		EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV;
-	page_ops = PAGE_UNLOCK | PAGE_START_WRITEBACK | PAGE_END_WRITEBACK;
-
 	/*
 	 * For the range (1). We have already instantiated the ordered extents
 	 * for this region. They are cleaned up by
 	 * btrfs_cleanup_ordered_extents() in e.g,
-	 * btrfs_run_delalloc_range(). EXTENT_LOCKED | EXTENT_DELALLOC are
-	 * already cleared in the above loop. And, EXTENT_DELALLOC_NEW |
-	 * EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV are handled by the cleanup
-	 * function.
+	 * btrfs_run_delalloc_range().
+	 * EXTENT_DELALLOC_NEW | EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV
+	 * are also handled by the cleanup function.
 	 *
-	 * However, in case of @keep_locked, we still need to unlock the pages
-	 * (except @locked_folio) to ensure all the pages are unlocked.
+	 * So here we only clear EXTENT_LOCKED and EXTENT_DELALLOC flag,
+	 * and finish the writeback of the involved folios, which will be
+	 * never submitted.
 	 */
-	if (keep_locked && orig_start < start) {
+	if (orig_start < start) {
+		clear_bits = EXTENT_LOCKED | EXTENT_DELALLOC;
+		page_ops = PAGE_UNLOCK | PAGE_START_WRITEBACK | PAGE_END_WRITEBACK;
+
 		if (!locked_folio)
 			mapping_set_error(inode->vfs_inode.i_mapping, ret);
 		extent_clear_unlock_delalloc(inode, orig_start, start - 1,
-					     locked_folio, NULL, 0, page_ops);
+					     locked_folio, NULL, clear_bits, page_ops);
 	}
 
-	/*
-	 * At this point we're unlocked, we want to make sure we're only
-	 * clearing these flags under the extent lock, so lock the rest of the
-	 * range and clear everything up.
-	 */
-	lock_extent(&inode->io_tree, start, end, NULL);
+	clear_bits = EXTENT_LOCKED | EXTENT_DELALLOC | EXTENT_DELALLOC_NEW |
+		EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV;
+	page_ops = PAGE_UNLOCK | PAGE_START_WRITEBACK | PAGE_END_WRITEBACK;
 
 	/*
 	 * For the range (2). If we reserved an extent for our delalloc range
-- 
2.47.1

[PATCH v4 05/10] btrfs: do proper folio cleanup when run_delalloc_nocow() failed

[Qu Wenruo]

[BUG]
With CONFIG_DEBUG_VM set, test case generic/476 has some chance to crash
with the following VM_BUG_ON_FOLIO():

 BTRFS error (device dm-3): cow_file_range failed, start 1146880 end 1253375 len 106496 ret -28
 BTRFS error (device dm-3): run_delalloc_nocow failed, start 1146880 end 1253375 len 106496 ret -28
 page: refcount:4 mapcount:0 mapping:00000000592787cc index:0x12 pfn:0x10664
 aops:btrfs_aops [btrfs] ino:101 dentry name(?):"f1774"
 flags: 0x2fffff80004028(uptodate|lru|private|node=0|zone=2|lastcpupid=0xfffff)
 page dumped because: VM_BUG_ON_FOLIO(!folio_test_locked(folio))
 ------------[ cut here ]------------
 kernel BUG at mm/page-writeback.c:2992!
 Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
 CPU: 2 UID: 0 PID: 3943513 Comm: kworker/u24:15 Tainted: G           OE      6.12.0-rc7-custom+ #87
 Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
 Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
 Workqueue: events_unbound btrfs_async_reclaim_data_space [btrfs]
 pc : folio_clear_dirty_for_io+0x128/0x258
 lr : folio_clear_dirty_for_io+0x128/0x258
 Call trace:
  folio_clear_dirty_for_io+0x128/0x258
  btrfs_folio_clamp_clear_dirty+0x80/0xd0 [btrfs]
  __process_folios_contig+0x154/0x268 [btrfs]
  extent_clear_unlock_delalloc+0x5c/0x80 [btrfs]
  run_delalloc_nocow+0x5f8/0x760 [btrfs]
  btrfs_run_delalloc_range+0xa8/0x220 [btrfs]
  writepage_delalloc+0x230/0x4c8 [btrfs]
  extent_writepage+0xb8/0x358 [btrfs]
  extent_write_cache_pages+0x21c/0x4e8 [btrfs]
  btrfs_writepages+0x94/0x150 [btrfs]
  do_writepages+0x74/0x190
  filemap_fdatawrite_wbc+0x88/0xc8
  start_delalloc_inodes+0x178/0x3a8 [btrfs]
  btrfs_start_delalloc_roots+0x174/0x280 [btrfs]
  shrink_delalloc+0x114/0x280 [btrfs]
  flush_space+0x250/0x2f8 [btrfs]
  btrfs_async_reclaim_data_space+0x180/0x228 [btrfs]
  process_one_work+0x164/0x408
  worker_thread+0x25c/0x388
  kthread+0x100/0x118
  ret_from_fork+0x10/0x20
 Code: 910a8021 a90363f7 a9046bf9 94012379 (d4210000)
 ---[ end trace 0000000000000000 ]---

[CAUSE]
The first two lines of extra debug messages show the problem is caused
by the error handling of run_delalloc_nocow().

E.g. we have the following dirtied range (4K blocksize 4K page size):

    0                 16K                  32K
    |//////////////////////////////////////|
    |  Pre-allocated  |

And the range [0, 16K) has a preallocated extent.

- Enter run_delalloc_nocow() for range [0, 16K)
  Which found range [0, 16K) is preallocated, can do the proper NOCOW
  write.

- Enter fallback_to_fow() for range [16K, 32K)
  Since the range [16K, 32K) is not backed by preallocated extent, we
  have to go COW.

- cow_file_range() failed for range [16K, 32K)
  So cow_file_range() will do the clean up by clearing folio dirty,
  unlock the folios.

  Now the folios in range [16K, 32K) is unlocked.

- Enter extent_clear_unlock_delalloc() from run_delalloc_nocow()
  Which is called with PAGE_START_WRITEBACK to start page writeback.
  But folios can only be marked writeback when it's properly locked,
  thus this triggered the VM_BUG_ON_FOLIO().

Furthermore there is another hidden but common bug that
run_delalloc_nocow() is not clearing the folio dirty flags in its error
handling path.
This is the common bug shared between run_delalloc_nocow() and
cow_file_range().

[FIX]
- Clear folio dirty for range [@start, @cur_offset)
  Introduce a helper, cleanup_dirty_folios(), which
  will find and lock the folio in the range, clear the dirty flag and
  start/end the writeback, with the extra handling for the
  @locked_folio.

- Introduce a helper to clear folio dirty, start and end writeback

- Introduce a helper to record the last failed COW range end
  This is to trace which range we should skip, to avoid double
  unlocking.

- Skip the failed COW range for the error handling

Cc: stable@vger.kernel.org
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c   | 98 ++++++++++++++++++++++++++++++++++++++++++----
 fs/btrfs/subpage.h | 13 ++++++
 2 files changed, 104 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index b94c4abcda3a..73a6b88c6511 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1957,6 +1957,54 @@ static int can_nocow_file_extent(struct btrfs_path *path,
 	return ret < 0 ? ret : can_nocow;
 }
 
+/*
+ * To cleanup the dirty folios which will never be submitted due to
+ * error.
+ *
+ * When running a delalloc range, we may need to split the ranges (due to
+ * fragmentation or NOCOW limit). If we hit an error in the later part,
+ * we will error out and previously successfully executed range will never
+ * be submitted, thus we have to cleanup those folios by clear their
+ * dirty flag, start and finish the writeback.
+ */
+static void cleanup_dirty_folios(struct btrfs_inode *inode,
+				 struct folio *locked_folio,
+				 u64 start, u64 end, int error)
+{
+	struct btrfs_fs_info *fs_info = inode->root->fs_info;
+	struct address_space *mapping = inode->vfs_inode.i_mapping;
+	pgoff_t start_index = start >> PAGE_SHIFT;
+	pgoff_t end_index = end >> PAGE_SHIFT;
+	u32 len;
+
+	ASSERT(end + 1 - start < U32_MAX);
+	ASSERT(IS_ALIGNED(start, fs_info->sectorsize) &&
+	       IS_ALIGNED(end + 1, fs_info->sectorsize));
+	len = end + 1 - start;
+
+	/*
+	 * Handle the locked folio first.
+	 * btrfs_folio_clamp_*() helpers can handle range out of the folio case.
+	 */
+	btrfs_folio_clamp_finish_io(fs_info, locked_folio, start, len);
+
+	for (pgoff_t index = start_index; index <= end_index; index++) {
+		struct folio *folio;
+
+		/* Already handled at the beginning. */
+		if (index == locked_folio->index)
+			continue;
+		folio = __filemap_get_folio(mapping, index, FGP_LOCK, GFP_NOFS);
+		/* Cache already dropped, no need to do any cleanup. */
+		if (IS_ERR(folio))
+			continue;
+		btrfs_folio_clamp_finish_io(fs_info, locked_folio, start, len);
+		folio_unlock(folio);
+		folio_put(folio);
+	}
+	mapping_set_error(mapping, error);
+}
+
 /*
  * when nowcow writeback call back.  This checks for snapshots or COW copies
  * of the extents that exist in the file, and COWs the file as required.
@@ -1972,6 +2020,11 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 	struct btrfs_root *root = inode->root;
 	struct btrfs_path *path;
 	u64 cow_start = (u64)-1;
+	/*
+	 * If not 0, represents the inclusive end of the last fallback_to_cow()
+	 * range. Only for error handling.
+	 */
+	u64 cow_end = 0;
 	u64 cur_offset = start;
 	int ret;
 	bool check_prev = true;
@@ -2132,6 +2185,7 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 					      found_key.offset - 1);
 			cow_start = (u64)-1;
 			if (ret) {
+				cow_end = found_key.offset - 1;
 				btrfs_dec_nocow_writers(nocow_bg);
 				goto error;
 			}
@@ -2205,11 +2259,12 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 		cow_start = cur_offset;
 
 	if (cow_start != (u64)-1) {
-		cur_offset = end;
 		ret = fallback_to_cow(inode, locked_folio, cow_start, end);
 		cow_start = (u64)-1;
-		if (ret)
+		if (ret) {
+			cow_end = end;
 			goto error;
+		}
 	}
 
 	btrfs_free_path(path);
@@ -2217,12 +2272,41 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 
 error:
 	/*
-	 * If an error happened while a COW region is outstanding, cur_offset
-	 * needs to be reset to cow_start to ensure the COW region is unlocked
-	 * as well.
+	 * There are several error cases:
+	 *
+	 * 1) Failed without falling back to COW
+	 *    start         cur_offset             end
+	 *    |/////////////|                      |
+	 *
+	 *    For range [start, cur_offset) the folios are already unlocked (except
+	 *    @locked_folio), EXTENT_DELALLOC already removed.
+	 *    Only need to clear the dirty flag as they will never be submitted.
+	 *    Ordered extent and extent maps are handled by
+	 *    btrfs_mark_ordered_io_finished() inside run_delalloc_range().
+	 *
+	 * 2) Failed with error from fallback_to_cow()
+	 *    start         cur_offset  cow_end    end
+	 *    |/////////////|-----------|          |
+	 *
+	 *    For range [start, cur_offset) it's the same as case 1).
+	 *    But for range [cur_offset, cow_end), the folios have dirty flag
+	 *    cleared and unlocked, EXTENT_DEALLLOC cleared by cow_file_range().
+	 *
+	 *    Thus we should not call extent_clear_unlock_delalloc() on range
+	 *    [cur_offset, cow_end), as the folios are already unlocked.
+	 *
+	 * So clear the folio dirty flags for [start, cur_offset) first.
 	 */
-	if (cow_start != (u64)-1)
-		cur_offset = cow_start;
+	if (cur_offset > start)
+		cleanup_dirty_folios(inode, locked_folio, start, cur_offset - 1, ret);
+
+	/*
+	 * If an error happened while a COW region is outstanding, cur_offset
+	 * needs to be reset to @cow_end + 1 to skip the COW range, as
+	 * cow_file_range() will do the proper cleanup at error.
+	 */
+	if (cow_end)
+		cur_offset = cow_end + 1;
 
 	/*
 	 * We need to lock the extent here because we're clearing DELALLOC and
diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index 428fa9389fd4..44fff1f4eac4 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -137,6 +137,19 @@ DECLARE_BTRFS_SUBPAGE_OPS(writeback);
 DECLARE_BTRFS_SUBPAGE_OPS(ordered);
 DECLARE_BTRFS_SUBPAGE_OPS(checked);
 
+/*
+ * Helper for error cleanup, where a folio will have its dirty flag cleared,
+ * with writeback started and finished.
+ */
+static inline void btrfs_folio_clamp_finish_io(struct btrfs_fs_info *fs_info,
+					       struct folio *locked_folio,
+					       u64 start, u32 len)
+{
+	btrfs_folio_clamp_clear_dirty(fs_info, locked_folio, start, len);
+	btrfs_folio_clamp_set_writeback(fs_info, locked_folio, start, len);
+	btrfs_folio_clamp_clear_writeback(fs_info, locked_folio, start, len);
+}
+
 bool btrfs_subpage_clear_and_test_dirty(const struct btrfs_fs_info *fs_info,
 					struct folio *folio, u64 start, u32 len);
 
-- 
2.47.1

[PATCH v4 06/10] btrfs: subpage: fix the bitmap dump for the locked flags

[Qu Wenruo]

We're dumping the locked bitmap into the @checked_bitmap variable,
causing incorrect values during debug.

Thankfuklly even during my development I haven't hit a case where I need
to dump the locked bitmap.
But for the sake of consistency, fix it by dumpping the locked bitmap
into @locked_bitmap variable for output.

Fixes: 75258f20fb70 ("btrfs: subpage: dump extra subpage bitmaps for debug")
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/subpage.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index 8c68059ac1b0..03d7bfc042e2 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -716,6 +716,7 @@ void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
 	unsigned long writeback_bitmap;
 	unsigned long ordered_bitmap;
 	unsigned long checked_bitmap;
+	unsigned long locked_bitmap;
 	unsigned long flags;
 
 	ASSERT(folio_test_private(folio) && folio_get_private(folio));
@@ -728,15 +729,16 @@ void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
 	GET_SUBPAGE_BITMAP(subpage, fs_info, writeback, &writeback_bitmap);
 	GET_SUBPAGE_BITMAP(subpage, fs_info, ordered, &ordered_bitmap);
 	GET_SUBPAGE_BITMAP(subpage, fs_info, checked, &checked_bitmap);
-	GET_SUBPAGE_BITMAP(subpage, fs_info, locked, &checked_bitmap);
+	GET_SUBPAGE_BITMAP(subpage, fs_info, locked, &locked_bitmap);
 	spin_unlock_irqrestore(&subpage->lock, flags);
 
 	dump_page(folio_page(folio, 0), "btrfs subpage dump");
 	btrfs_warn(fs_info,
-"start=%llu len=%u page=%llu, bitmaps uptodate=%*pbl dirty=%*pbl writeback=%*pbl ordered=%*pbl checked=%*pbl",
+"start=%llu len=%u page=%llu, bitmaps uptodate=%*pbl dirty=%*pbl locked=%*pbl writeback=%*pbl ordered=%*pbl checked=%*pbl",
 		    start, len, folio_pos(folio),
 		    sectors_per_page, &uptodate_bitmap,
 		    sectors_per_page, &dirty_bitmap,
+		    sectors_per_page, &locked_bitmap,
 		    sectors_per_page, &writeback_bitmap,
 		    sectors_per_page, &ordered_bitmap,
 		    sectors_per_page, &checked_bitmap);
-- 
2.47.1

[PATCH v4 07/10] btrfs: subpage: dump the involved bitmap when ASSERT() failed

[Qu Wenruo]

For btrfs_folio_assert_not_dirty() and btrfs_folio_set_lock(), we call
bitmap_test_range_all_zero() to ensure the involved range has no
dirty/lock bit already set.

However with my recent enhanced delalloc range error handling, I was
hitting the ASSERT() inside btrfs_folio_set_lock(), and it turns out
that some error handling path is not properly update the folio flags.

So add some extra dumpping for the ASSERTs to dump the involved bitmap
to help debug.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/subpage.c | 41 ++++++++++++++++++++++++++++++-----------
 1 file changed, 30 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index 03d7bfc042e2..5d088f7d6184 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -635,6 +635,28 @@ IMPLEMENT_BTRFS_PAGE_OPS(ordered, folio_set_ordered, folio_clear_ordered,
 IMPLEMENT_BTRFS_PAGE_OPS(checked, folio_set_checked, folio_clear_checked,
 			 folio_test_checked);
 
+#define GET_SUBPAGE_BITMAP(subpage, fs_info, name, dst)			\
+{									\
+	const int sectors_per_page = fs_info->sectors_per_page;		\
+									\
+	ASSERT(sectors_per_page < BITS_PER_LONG);			\
+	*dst = bitmap_read(subpage->bitmaps,				\
+			   sectors_per_page * btrfs_bitmap_nr_##name,	\
+			   sectors_per_page);				\
+}
+
+#define subpage_dump_bitmap(fs_info, folio, name, start, len)		\
+{									\
+	struct btrfs_subpage *subpage = folio_get_private(folio);	\
+	unsigned long bitmap;						\
+									\
+	GET_SUBPAGE_BITMAP(subpage, fs_info, name, &bitmap);		\
+	btrfs_warn(fs_info,						\
+	"dumpping bitmap start=%llu len=%u folio=%llu " #name "_bitmap=%*pbl", \
+		   start, len, folio_pos(folio),			\
+		   fs_info->sectors_per_page, &bitmap);			\
+}
+
 /*
  * Make sure not only the page dirty bit is cleared, but also subpage dirty bit
  * is cleared.
@@ -660,6 +682,10 @@ void btrfs_folio_assert_not_dirty(const struct btrfs_fs_info *fs_info,
 	subpage = folio_get_private(folio);
 	ASSERT(subpage);
 	spin_lock_irqsave(&subpage->lock, flags);
+	if (unlikely(!bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits))) {
+		subpage_dump_bitmap(fs_info, folio, dirty, start, len);
+		ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
+	}
 	ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
 	spin_unlock_irqrestore(&subpage->lock, flags);
 }
@@ -689,23 +715,16 @@ void btrfs_folio_set_lock(const struct btrfs_fs_info *fs_info,
 	nbits = len >> fs_info->sectorsize_bits;
 	spin_lock_irqsave(&subpage->lock, flags);
 	/* Target range should not yet be locked. */
-	ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
+	if (unlikely(!bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits))) {
+		subpage_dump_bitmap(fs_info, folio, locked, start, len);
+		ASSERT(bitmap_test_range_all_zero(subpage->bitmaps, start_bit, nbits));
+	}
 	bitmap_set(subpage->bitmaps, start_bit, nbits);
 	ret = atomic_add_return(nbits, &subpage->nr_locked);
 	ASSERT(ret <= fs_info->sectors_per_page);
 	spin_unlock_irqrestore(&subpage->lock, flags);
 }
 
-#define GET_SUBPAGE_BITMAP(subpage, fs_info, name, dst)			\
-{									\
-	const int sectors_per_page = fs_info->sectors_per_page;		\
-									\
-	ASSERT(sectors_per_page < BITS_PER_LONG);			\
-	*dst = bitmap_read(subpage->bitmaps,				\
-			   sectors_per_page * btrfs_bitmap_nr_##name,	\
-			   sectors_per_page);				\
-}
-
 void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
 				      struct folio *folio, u64 start, u32 len)
 {
-- 
2.47.1

[PATCH v4 08/10] btrfs: add extra error messages for delalloc range related errors

[Qu Wenruo]

All the error handling bugs I hit so far are all -ENOSPC from either:

- cow_file_range()
- run_delalloc_nocow()
- submit_uncompressed_range()

Previously when those functions failed, there is no error message at
all, making the debugging much harder.

So here we introduce extra error messages for:

- cow_file_range()
- run_delalloc_nocow()
- submit_uncompressed_range()
- writepage_delalloc() when btrfs_run_delalloc_range() failed
- extent_writepage() when extent_writepage_io() failed

One example of the new debug error messages is the following one:

 run fstests generic/750 at 2024-12-08 12:41:41
 BTRFS: device fsid 461b25f5-e240-4543-8deb-e7c2bd01a6d3 devid 1 transid 8 /dev/mapper/test-scratch1 (253:4) scanned by mount (2436600)
 BTRFS info (device dm-4): first mount of filesystem 461b25f5-e240-4543-8deb-e7c2bd01a6d3
 BTRFS info (device dm-4): using crc32c (crc32c-arm64) checksum algorithm
 BTRFS info (device dm-4): forcing free space tree for sector size 4096 with page size 65536
 BTRFS info (device dm-4): using free-space-tree
 BTRFS warning (device dm-4): read-write for sector size 4096 with page size 65536 is experimental
 BTRFS info (device dm-4): checking UUID tree
 BTRFS error (device dm-4): cow_file_range failed, root=363 inode=412 start=503808 len=98304: -28
 BTRFS error (device dm-4): run_delalloc_nocow failed, root=363 inode=412 start=503808 len=98304: -28
 BTRFS error (device dm-4): failed to run delalloc range, root=363 ino=412 folio=458752 submit_bitmap=11-15 start=503808 len=98304: -28

Which shows an error from cow_file_range() which is called inside a
nocow write attempt, along with the extra bitmap from
writepage_delalloc().

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 16 ++++++++++++++++
 fs/btrfs/inode.c     | 12 ++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f50e4fccd909..72342663341c 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1255,6 +1255,15 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
 						       wbc);
 			if (ret >= 0)
 				last_finished_delalloc_end = found_start + found_len;
+			if (unlikely(ret < 0))
+				btrfs_err_rl(fs_info,
+"failed to run delalloc range, root=%lld ino=%llu folio=%llu submit_bitmap=%*pbl start=%llu len=%u: %d",
+					     btrfs_root_id(inode->root),
+					     btrfs_ino(inode),
+					     folio_pos(folio),
+					     fs_info->sectors_per_page,
+					     &bio_ctrl->submit_bitmap,
+					     found_start, found_len, ret);
 		} else {
 			/*
 			 * We've hit an error during previous delalloc range,
@@ -1553,6 +1562,13 @@ static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl
 				  PAGE_SIZE, bio_ctrl, i_size);
 	if (ret == 1)
 		return 0;
+	if (ret < 0)
+		btrfs_err_rl(fs_info,
+"failed to submit blocks, root=%lld inode=%llu folio=%llu submit_bitmap=%*pbl: %d",
+			     btrfs_root_id(inode->root),
+			     btrfs_ino(inode),
+			     folio_pos(folio), fs_info->sectors_per_page,
+			     &bio_ctrl->submit_bitmap, ret);
 
 	bio_ctrl->wbc->nr_to_write--;
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 73a6b88c6511..3409f1e02de0 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1133,6 +1133,10 @@ static void submit_uncompressed_range(struct btrfs_inode *inode,
 		if (locked_folio)
 			btrfs_folio_end_lock(inode->root->fs_info, locked_folio,
 					     start, async_extent->ram_size);
+		btrfs_err_rl(inode->root->fs_info,
+		"%s failed, root=%llu inode=%llu start=%llu len=%llu: %d",
+			     __func__, btrfs_root_id(inode->root),
+			     btrfs_ino(inode), start, async_extent->ram_size, ret);
 	}
 }
 
@@ -1579,6 +1583,10 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 		btrfs_qgroup_free_data(inode, NULL, start + cur_alloc_size,
 				       end - start - cur_alloc_size + 1, NULL);
 	}
+	btrfs_err_rl(fs_info,
+		     "%s failed, root=%llu inode=%llu start=%llu len=%llu: %d",
+		     __func__, btrfs_root_id(inode->root),
+		     btrfs_ino(inode), orig_start, end + 1 - orig_start, ret);
 	return ret;
 }
 
@@ -2326,6 +2334,10 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 		btrfs_qgroup_free_data(inode, NULL, cur_offset, end - cur_offset + 1, NULL);
 	}
 	btrfs_free_path(path);
+	btrfs_err_rl(fs_info,
+		     "%s failed, root=%llu inode=%llu start=%llu len=%llu: %d",
+		     __func__, btrfs_root_id(inode->root),
+		     btrfs_ino(inode), start, end + 1 - start, ret);
 	return ret;
 }
 
-- 
2.47.1

[PATCH v4 09/10] btrfs: remove the unused @locked_folio parameter from btrfs_cleanup_ordered_extents()

[Qu Wenruo]

The function btrfs_cleanup_ordered_extents() is only called in error
handling path, and the last caller with a @locked_folio parameter is
removed to fix a bug in the btrfs_run_delalloc_range() error handling.

There is no need to pass @locked_folio parameter anymore.

Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c | 44 ++------------------------------------------
 1 file changed, 2 insertions(+), 42 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 3409f1e02de0..130f0490b14f 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -393,34 +393,13 @@ void btrfs_inode_unlock(struct btrfs_inode *inode, unsigned int ilock_flags)
  * extent (btrfs_finish_ordered_io()).
  */
 static inline void btrfs_cleanup_ordered_extents(struct btrfs_inode *inode,
-						 struct folio *locked_folio,
 						 u64 offset, u64 bytes)
 {
 	unsigned long index = offset >> PAGE_SHIFT;
 	unsigned long end_index = (offset + bytes - 1) >> PAGE_SHIFT;
-	u64 page_start = 0, page_end = 0;
 	struct folio *folio;
 
-	if (locked_folio) {
-		page_start = folio_pos(locked_folio);
-		page_end = page_start + folio_size(locked_folio) - 1;
-	}
-
 	while (index <= end_index) {
-		/*
-		 * For locked page, we will call btrfs_mark_ordered_io_finished
-		 * through btrfs_mark_ordered_io_finished() on it
-		 * in run_delalloc_range() for the error handling, which will
-		 * clear page Ordered and run the ordered extent accounting.
-		 *
-		 * Here we can't just clear the Ordered bit, or
-		 * btrfs_mark_ordered_io_finished() would skip the accounting
-		 * for the page range, and the ordered extent will never finish.
-		 */
-		if (locked_folio && index == (page_start >> PAGE_SHIFT)) {
-			index++;
-			continue;
-		}
 		folio = filemap_get_folio(inode->vfs_inode.i_mapping, index);
 		index++;
 		if (IS_ERR(folio))
@@ -436,23 +415,6 @@ static inline void btrfs_cleanup_ordered_extents(struct btrfs_inode *inode,
 		folio_put(folio);
 	}
 
-	if (locked_folio) {
-		/* The locked page covers the full range, nothing needs to be done */
-		if (bytes + offset <= page_start + folio_size(locked_folio))
-			return;
-		/*
-		 * In case this page belongs to the delalloc range being
-		 * instantiated then skip it, since the first page of a range is
-		 * going to be properly cleaned up by the caller of
-		 * run_delalloc_range
-		 */
-		if (page_start >= offset && page_end <= (offset + bytes - 1)) {
-			bytes = offset + bytes - folio_pos(locked_folio) -
-				folio_size(locked_folio);
-			offset = folio_pos(locked_folio) + folio_size(locked_folio);
-		}
-	}
-
 	return btrfs_mark_ordered_io_finished(inode, NULL, offset, bytes, false);
 }
 
@@ -1128,8 +1090,7 @@ static void submit_uncompressed_range(struct btrfs_inode *inode,
 			       &wbc, false);
 	wbc_detach_inode(&wbc);
 	if (ret < 0) {
-		btrfs_cleanup_ordered_extents(inode, NULL,
-					      start, end - start + 1);
+		btrfs_cleanup_ordered_extents(inode, start, end - start + 1);
 		if (locked_folio)
 			btrfs_folio_end_lock(inode->root->fs_info, locked_folio,
 					     start, async_extent->ram_size);
@@ -2388,8 +2349,7 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct folio *locked_fol
 
 out:
 	if (ret < 0)
-		btrfs_cleanup_ordered_extents(inode, NULL, start,
-					      end - start + 1);
+		btrfs_cleanup_ordered_extents(inode, start, end - start + 1);
 	return ret;
 }
 
-- 
2.47.1

[PATCH v4 10/10] btrfs: move ordered extent cleanup to where they are allocated

[Qu Wenruo]

The ordered extent cleanup is hard to grasp because it doesn't follow
the common pattern that the cleanup happens where ordered extent get
allocated.

E.g. run_delalloc_nocow() and cow_file_range() allocate one or more
ordered extents, but if any error is hit, the cleanup is done inside
btrfs_run_delalloc_range().

To fix the existing delayed cleanup:

- Update the comment on error handling
  For @cow_start set case, @cur_offset can be assigned to either
  @cow_start or @cow_end.
  So for such case we can not trust @cur_offset but only @cow_start.

- Only reset @cow_start when fallback_to_cow() succeeded

- Add Extra ASSERT() when @cow_start is still set at error path

- Rewind @cur_offset when @cow_start is set
  When we fall back to COW, @cur_offset can be set to either @cow_start
  or @cow_end.
  We can not directly trust @cur_offset, or we will do double ordered
  extent accounting on range which is already cleaned up
  cow_file_range().

- Move btrfs_cleanup_ordered_extents() into run_delalloc_nocow() and
  cow_file_range()

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/inode.c | 58 +++++++++++++++++++++++++++++-------------------
 1 file changed, 35 insertions(+), 23 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 130f0490b14f..70ef7f59b692 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -1272,10 +1272,8 @@ u64 btrfs_get_extent_allocation_hint(struct btrfs_inode *inode, u64 start,
  * - Else all pages except for @locked_folio are unlocked.
  *
  * When a failure happens in the second or later iteration of the
- * while-loop, the ordered extents created in previous iterations are kept
- * intact. So, the caller must clean them up by calling
- * btrfs_cleanup_ordered_extents(). See btrfs_run_delalloc_range() for
- * example.
+ * while-loop, the ordered extents created in previous iterations are
+ * cleaned up, leaving no ordered extent in the range.
  */
 static noinline int cow_file_range(struct btrfs_inode *inode,
 				   struct folio *locked_folio, u64 start,
@@ -1488,9 +1486,7 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 
 	/*
 	 * For the range (1). We have already instantiated the ordered extents
-	 * for this region. They are cleaned up by
-	 * btrfs_cleanup_ordered_extents() in e.g,
-	 * btrfs_run_delalloc_range().
+	 * for this region, and need to clean them up.
 	 * EXTENT_DELALLOC_NEW | EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV
 	 * are also handled by the cleanup function.
 	 *
@@ -1504,6 +1500,8 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 
 		if (!locked_folio)
 			mapping_set_error(inode->vfs_inode.i_mapping, ret);
+
+		btrfs_cleanup_ordered_extents(inode, orig_start, start - orig_start);
 		extent_clear_unlock_delalloc(inode, orig_start, start - 1,
 					     locked_folio, NULL, clear_bits, page_ops);
 	}
@@ -1980,6 +1978,9 @@ static void cleanup_dirty_folios(struct btrfs_inode *inode,
  *
  * If no cow copies or snapshots exist, we write directly to the existing
  * blocks on disk
+ *
+ * If an error is hit, any ordered extent created inside the range is
+ * properly cleaned up.
  */
 static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 				       struct folio *locked_folio,
@@ -2152,12 +2153,12 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 		if (cow_start != (u64)-1) {
 			ret = fallback_to_cow(inode, locked_folio, cow_start,
 					      found_key.offset - 1);
-			cow_start = (u64)-1;
 			if (ret) {
 				cow_end = found_key.offset - 1;
 				btrfs_dec_nocow_writers(nocow_bg);
 				goto error;
 			}
+			cow_start = (u64)-1;
 		}
 
 		nocow_end = cur_offset + nocow_args.file_extent.num_bytes - 1;
@@ -2229,11 +2230,11 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 
 	if (cow_start != (u64)-1) {
 		ret = fallback_to_cow(inode, locked_folio, cow_start, end);
-		cow_start = (u64)-1;
 		if (ret) {
 			cow_end = end;
 			goto error;
 		}
+		cow_start = (u64)-1;
 	}
 
 	btrfs_free_path(path);
@@ -2249,25 +2250,40 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
 	 *
 	 *    For range [start, cur_offset) the folios are already unlocked (except
 	 *    @locked_folio), EXTENT_DELALLOC already removed.
-	 *    Only need to clear the dirty flag as they will never be submitted.
-	 *    Ordered extent and extent maps are handled by
-	 *    btrfs_mark_ordered_io_finished() inside run_delalloc_range().
+	 *    Need to finish the ordered extents and their extent maps, then
+	 *    clear the dirty flag as they will never to submitted.
 	 *
 	 * 2) Failed with error from fallback_to_cow()
-	 *    start         cur_offset  cow_end    end
+	 *    start         cow_start  cow_end    end
 	 *    |/////////////|-----------|          |
 	 *
-	 *    For range [start, cur_offset) it's the same as case 1).
-	 *    But for range [cur_offset, cow_end), the folios have dirty flag
+	 *    Special note for this case, @cur_offset may be set to either
+	 *    @cow_end or @cow_start.
+	 *    So for such fallback_to_cow() case, we should not trust @cur_offset
+	 *    but @cow_start.
+	 *    For range [start, cow_start) it's the same as case 1).
+	 *    But for range [cow_start, cow_end), the folios have dirty flag
 	 *    cleared and unlocked, EXTENT_DEALLLOC cleared by cow_file_range().
 	 *
 	 *    Thus we should not call extent_clear_unlock_delalloc() on range
-	 *    [cur_offset, cow_end), as the folios are already unlocked.
+	 *    [cow_start, cow_end), as the folios are already unlocked.
 	 *
-	 * So clear the folio dirty flags for [start, cur_offset) first.
+	 * So clear the folio dirty flags for [start, cur_offset) and finish
+	 * involved ordered extents.
+	 *
+	 * There is a special handling for COW case, where we advanced cur_offset to
+	 * the COW end already. For those cases we need to rewind the cur_offset to
+	 * the real correct location.
 	 */
-	if (cur_offset > start)
+	if (cow_start != (u64)-1) {
+		ASSERT(cow_end);
+		ASSERT(cur_offset >= cow_start);
+		cur_offset = cow_start;
+	}
+	if (cur_offset > start) {
+		btrfs_cleanup_ordered_extents(inode, start, cur_offset - start);
 		cleanup_dirty_folios(inode, locked_folio, start, cur_offset - 1, ret);
+	}
 
 	/*
 	 * If an error happened while a COW region is outstanding, cur_offset
@@ -2332,7 +2348,7 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct folio *locked_fol
 
 	if (should_nocow(inode, start, end)) {
 		ret = run_delalloc_nocow(inode, locked_folio, start, end);
-		goto out;
+		return ret;
 	}
 
 	if (btrfs_inode_can_compress(inode) &&
@@ -2346,10 +2362,6 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct folio *locked_fol
 	else
 		ret = cow_file_range(inode, locked_folio, start, end, NULL,
 				     false, false);
-
-out:
-	if (ret < 0)
-		btrfs_cleanup_ordered_extents(inode, start, end - start + 1);
 	return ret;
 }
 
-- 
2.47.1

Re: [PATCH v4 10/10] btrfs: move ordered extent cleanup to where they are allocated

[Qu Wenruo]

I'll drop this patch from the series.

The run_delalloc_nocow() is really a mess to fix.

It has too many weird error path that can screw up the ordered extent 
cleanup.
E.g. in must_cow: tag, we can set @cow_start, but without setting a 
proper @cow_end, causing us much harder to properly skip any COW range.

I'll need a dedicated patch to refactor run_delalloc_nocow() to make it 
more streamlined to handle nocow and COW fallback (other than the 
current cursed way).

Thanks,
Qu

在 2025/1/11 21:13, Qu Wenruo 写道:
> The ordered extent cleanup is hard to grasp because it doesn't follow
> the common pattern that the cleanup happens where ordered extent get
> allocated.
> 
> E.g. run_delalloc_nocow() and cow_file_range() allocate one or more
> ordered extents, but if any error is hit, the cleanup is done inside
> btrfs_run_delalloc_range().
> 
> To fix the existing delayed cleanup:
> 
> - Update the comment on error handling
>    For @cow_start set case, @cur_offset can be assigned to either
>    @cow_start or @cow_end.
>    So for such case we can not trust @cur_offset but only @cow_start.
> 
> - Only reset @cow_start when fallback_to_cow() succeeded
> 
> - Add Extra ASSERT() when @cow_start is still set at error path
> 
> - Rewind @cur_offset when @cow_start is set
>    When we fall back to COW, @cur_offset can be set to either @cow_start
>    or @cow_end.
>    We can not directly trust @cur_offset, or we will do double ordered
>    extent accounting on range which is already cleaned up
>    cow_file_range().
> 
> - Move btrfs_cleanup_ordered_extents() into run_delalloc_nocow() and
>    cow_file_range()
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/inode.c | 58 +++++++++++++++++++++++++++++-------------------
>   1 file changed, 35 insertions(+), 23 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 130f0490b14f..70ef7f59b692 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -1272,10 +1272,8 @@ u64 btrfs_get_extent_allocation_hint(struct btrfs_inode *inode, u64 start,
>    * - Else all pages except for @locked_folio are unlocked.
>    *
>    * When a failure happens in the second or later iteration of the
> - * while-loop, the ordered extents created in previous iterations are kept
> - * intact. So, the caller must clean them up by calling
> - * btrfs_cleanup_ordered_extents(). See btrfs_run_delalloc_range() for
> - * example.
> + * while-loop, the ordered extents created in previous iterations are
> + * cleaned up, leaving no ordered extent in the range.
>    */
>   static noinline int cow_file_range(struct btrfs_inode *inode,
>   				   struct folio *locked_folio, u64 start,
> @@ -1488,9 +1486,7 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
>   
>   	/*
>   	 * For the range (1). We have already instantiated the ordered extents
> -	 * for this region. They are cleaned up by
> -	 * btrfs_cleanup_ordered_extents() in e.g,
> -	 * btrfs_run_delalloc_range().
> +	 * for this region, and need to clean them up.
>   	 * EXTENT_DELALLOC_NEW | EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV
>   	 * are also handled by the cleanup function.
>   	 *
> @@ -1504,6 +1500,8 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
>   
>   		if (!locked_folio)
>   			mapping_set_error(inode->vfs_inode.i_mapping, ret);
> +
> +		btrfs_cleanup_ordered_extents(inode, orig_start, start - orig_start);
>   		extent_clear_unlock_delalloc(inode, orig_start, start - 1,
>   					     locked_folio, NULL, clear_bits, page_ops);
>   	}
> @@ -1980,6 +1978,9 @@ static void cleanup_dirty_folios(struct btrfs_inode *inode,
>    *
>    * If no cow copies or snapshots exist, we write directly to the existing
>    * blocks on disk
> + *
> + * If an error is hit, any ordered extent created inside the range is
> + * properly cleaned up.
>    */
>   static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
>   				       struct folio *locked_folio,
> @@ -2152,12 +2153,12 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
>   		if (cow_start != (u64)-1) {
>   			ret = fallback_to_cow(inode, locked_folio, cow_start,
>   					      found_key.offset - 1);
> -			cow_start = (u64)-1;
>   			if (ret) {
>   				cow_end = found_key.offset - 1;
>   				btrfs_dec_nocow_writers(nocow_bg);
>   				goto error;
>   			}
> +			cow_start = (u64)-1;
>   		}
>   
>   		nocow_end = cur_offset + nocow_args.file_extent.num_bytes - 1;
> @@ -2229,11 +2230,11 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
>   
>   	if (cow_start != (u64)-1) {
>   		ret = fallback_to_cow(inode, locked_folio, cow_start, end);
> -		cow_start = (u64)-1;
>   		if (ret) {
>   			cow_end = end;
>   			goto error;
>   		}
> +		cow_start = (u64)-1;
>   	}
>   
>   	btrfs_free_path(path);
> @@ -2249,25 +2250,40 @@ static noinline int run_delalloc_nocow(struct btrfs_inode *inode,
>   	 *
>   	 *    For range [start, cur_offset) the folios are already unlocked (except
>   	 *    @locked_folio), EXTENT_DELALLOC already removed.
> -	 *    Only need to clear the dirty flag as they will never be submitted.
> -	 *    Ordered extent and extent maps are handled by
> -	 *    btrfs_mark_ordered_io_finished() inside run_delalloc_range().
> +	 *    Need to finish the ordered extents and their extent maps, then
> +	 *    clear the dirty flag as they will never to submitted.
>   	 *
>   	 * 2) Failed with error from fallback_to_cow()
> -	 *    start         cur_offset  cow_end    end
> +	 *    start         cow_start  cow_end    end
>   	 *    |/////////////|-----------|          |
>   	 *
> -	 *    For range [start, cur_offset) it's the same as case 1).
> -	 *    But for range [cur_offset, cow_end), the folios have dirty flag
> +	 *    Special note for this case, @cur_offset may be set to either
> +	 *    @cow_end or @cow_start.
> +	 *    So for such fallback_to_cow() case, we should not trust @cur_offset
> +	 *    but @cow_start.
> +	 *    For range [start, cow_start) it's the same as case 1).
> +	 *    But for range [cow_start, cow_end), the folios have dirty flag
>   	 *    cleared and unlocked, EXTENT_DEALLLOC cleared by cow_file_range().
>   	 *
>   	 *    Thus we should not call extent_clear_unlock_delalloc() on range
> -	 *    [cur_offset, cow_end), as the folios are already unlocked.
> +	 *    [cow_start, cow_end), as the folios are already unlocked.
>   	 *
> -	 * So clear the folio dirty flags for [start, cur_offset) first.
> +	 * So clear the folio dirty flags for [start, cur_offset) and finish
> +	 * involved ordered extents.
> +	 *
> +	 * There is a special handling for COW case, where we advanced cur_offset to
> +	 * the COW end already. For those cases we need to rewind the cur_offset to
> +	 * the real correct location.
>   	 */
> -	if (cur_offset > start)
> +	if (cow_start != (u64)-1) {
> +		ASSERT(cow_end);
> +		ASSERT(cur_offset >= cow_start);
> +		cur_offset = cow_start;
> +	}
> +	if (cur_offset > start) {
> +		btrfs_cleanup_ordered_extents(inode, start, cur_offset - start);
>   		cleanup_dirty_folios(inode, locked_folio, start, cur_offset - 1, ret);
> +	}
>   
>   	/*
>   	 * If an error happened while a COW region is outstanding, cur_offset
> @@ -2332,7 +2348,7 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct folio *locked_fol
>   
>   	if (should_nocow(inode, start, end)) {
>   		ret = run_delalloc_nocow(inode, locked_folio, start, end);
> -		goto out;
> +		return ret;
>   	}
>   
>   	if (btrfs_inode_can_compress(inode) &&
> @@ -2346,10 +2362,6 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct folio *locked_fol
>   	else
>   		ret = cow_file_range(inode, locked_folio, start, end, NULL,
>   				     false, false);
> -
> -out:
> -	if (ret < 0)
> -		btrfs_cleanup_ordered_extents(inode, start, end - start + 1);
>   	return ret;
>   }
>