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btrfs: fix double accounting of ordered extents during errors
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[BUG]
Btrfs will fail generic/750 randomly if its sector size is smaller than
page size.

One of the warning looks like this:

 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 90263 at fs/btrfs/ordered-data.c:360 can_finish_ordered_extent+0x33c/0x390 [btrfs]
 CPU: 1 UID: 0 PID: 90263 Comm: kworker/u18:1 Tainted: G           OE      6.12.0-rc3-custom+ torvalds#79
 Workqueue: events_unbound btrfs_async_reclaim_metadata_space [btrfs]
 pc : can_finish_ordered_extent+0x33c/0x390 [btrfs]
 lr : can_finish_ordered_extent+0xdc/0x390 [btrfs]
 Call trace:
  can_finish_ordered_extent+0x33c/0x390 [btrfs]
  btrfs_mark_ordered_io_finished+0x130/0x2b8 [btrfs]
  extent_writepage+0xfc/0x338 [btrfs]
  extent_write_cache_pages+0x1d4/0x4b8 [btrfs]
  btrfs_writepages+0x94/0x158 [btrfs]
  do_writepages+0x74/0x190
  filemap_fdatawrite_wbc+0x88/0xc8
  start_delalloc_inodes+0x180/0x3b0 [btrfs]
  btrfs_start_delalloc_roots+0x17c/0x288 [btrfs]
  shrink_delalloc+0x11c/0x280 [btrfs]
  flush_space+0x27c/0x310 [btrfs]
  btrfs_async_reclaim_metadata_space+0xcc/0x208 [btrfs]
  process_one_work+0x228/0x670
  worker_thread+0x1bc/0x360
  kthread+0x100/0x118
  ret_from_fork+0x10/0x20
 irq event stamp: 9784200
 hardirqs last  enabled at (9784199): [<ffffd21ec54dc01c>] _raw_spin_unlock_irqrestore+0x74/0x80
 hardirqs last disabled at (9784200): [<ffffd21ec54db374>] _raw_spin_lock_irqsave+0x8c/0xa0
 softirqs last  enabled at (9784148): [<ffffd21ec472ff44>] handle_softirqs+0x45c/0x4b0
 softirqs last disabled at (9784141): [<ffffd21ec46d01e4>] __do_softirq+0x1c/0x28
 ---[ end trace 0000000000000000 ]---
 BTRFS critical (device dm-2): bad ordered extent accounting, root=5 ino=1492 OE offset=1654784 OE len=57344 to_dec=49152 left=0

[CAUSE]
The function btrfs_mark_ordered_io_finished() is called for marking all
ordered extents in the page range as finished, for error handling.

But for sector size < page size cases, we can have multiple ordered
extents in one page.

If extent_writepage_io() failed (the only possible case is
submit_one_sector() failed to grab an extent map), then the call site
inside extent_writepage() will call btrfs_mark_ordered_io_finished() to
finish the created ordered extents.

However some range of the ordered extent may have been submitted already,
then btrfs_mark_ordered_io_finished() is called on the same range, causing
double accounting.

[FIX]
- Introduce a new member btrfs_bio_ctrl::last_submitted
  This will trace the last sector submitted through
  extent_writepage_io().

  So for the above extent_writepage() case, we will know exactly which
  sectors are submitted and should not do the ordered extent accounting.

- Introduce a helper cleanup_ordered_extents()
  This will do a sector-by-sector cleanup with
  btrfs_bio_ctrl::last_submitted and btrfs_bio_ctrl::submit_bitmap into
  consideartion.

  Using @last_submitted is to avoid double accounting on the submitted
  ranges.
  Meanwhile using @submit_bitmap is to avoid touching ranges going
  through compression.

Signed-off-by: Qu Wenruo <wqu@suse.com>
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adam900710 authored and intel-lab-lkp committed Oct 28, 2024
1 parent 34e6ef8 commit ccb56db
Showing 1 changed file with 37 additions and 4 deletions.
41 changes: 37 additions & 4 deletions fs/btrfs/extent_io.c
Original file line number Diff line number Diff line change
@@ -108,6 +108,14 @@ struct btrfs_bio_ctrl {
* This is to avoid touching ranges covered by compression/inline.
*/
unsigned long submit_bitmap;

/*
* The end (exclusive) of the last submitted range in the folio.
*
* This is for sector size < page size case where we may hit error
* half way.
*/
u64 last_submitted;
};

static void submit_one_bio(struct btrfs_bio_ctrl *bio_ctrl)
@@ -1436,6 +1444,7 @@ static noinline_for_stack int extent_writepage_io(struct btrfs_inode *inode,
ret = submit_one_sector(inode, folio, cur, bio_ctrl, i_size);
if (ret < 0)
goto out;
bio_ctrl->last_submitted = cur + fs_info->sectorsize;
submitted_io = true;
}
out:
@@ -1454,6 +1463,24 @@ static noinline_for_stack int extent_writepage_io(struct btrfs_inode *inode,
return ret;
}

static void cleanup_ordered_extents(struct btrfs_inode *inode,
struct folio *folio, u64 file_pos,
u64 num_bytes, unsigned long *bitmap)
{
struct btrfs_fs_info *fs_info = inode->root->fs_info;
unsigned int cur_bit = (file_pos - folio_pos(folio)) >> fs_info->sectorsize_bits;

for_each_set_bit_from(cur_bit, bitmap, fs_info->sectors_per_page) {
u64 cur_pos = folio_pos(folio) + (cur_bit << fs_info->sectorsize_bits);

if (cur_pos >= file_pos + num_bytes)
break;

btrfs_mark_ordered_io_finished(inode, folio, cur_pos,
fs_info->sectorsize, false);
}
}

/*
* the writepage semantics are similar to regular writepage. extent
* records are inserted to lock ranges in the tree, and as dirty areas
@@ -1493,6 +1520,7 @@ static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl
* The proper bitmap can only be initialized until writepage_delalloc().
*/
bio_ctrl->submit_bitmap = (unsigned long)-1;
bio_ctrl->last_submitted = page_start;
ret = set_folio_extent_mapped(folio);
if (ret < 0)
goto done;
@@ -1512,8 +1540,10 @@ static int extent_writepage(struct folio *folio, struct btrfs_bio_ctrl *bio_ctrl

done:
if (ret) {
btrfs_mark_ordered_io_finished(BTRFS_I(inode), folio,
page_start, PAGE_SIZE, !ret);
cleanup_ordered_extents(BTRFS_I(inode), folio,
bio_ctrl->last_submitted,
page_start + PAGE_SIZE - bio_ctrl->last_submitted,
&bio_ctrl->submit_bitmap);
mapping_set_error(folio->mapping, ret);
}

@@ -2289,14 +2319,17 @@ void extent_write_locked_range(struct inode *inode, const struct folio *locked_f
* extent_writepage_io() will do the truncation correctly.
*/
bio_ctrl.submit_bitmap = (unsigned long)-1;
bio_ctrl.last_submitted = cur;
ret = extent_writepage_io(BTRFS_I(inode), folio, cur, cur_len,
&bio_ctrl, i_size);
if (ret == 1)
goto next_page;

if (ret) {
btrfs_mark_ordered_io_finished(BTRFS_I(inode), folio,
cur, cur_len, !ret);
cleanup_ordered_extents(BTRFS_I(inode), folio,
bio_ctrl.last_submitted,
cur_end + 1 - bio_ctrl.last_submitted,
&bio_ctrl.submit_bitmap);
mapping_set_error(mapping, ret);
}
btrfs_folio_end_lock(fs_info, folio, cur, cur_len);

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