[BUG]
There are several double accounting case, where the WARN_ON_ONCE() is
triggered inside can_finish_ordered_extent().
And all such cases points back to the btrfs_mark_ordered_io_finished()
call inside extent_writepage() when it hits some error.
[CAUSE]
With extra debug patches to show where the error is from, it turns out
to be btrfs_run_delalloc_range() can fail with -ENOSPC.
Such failure itself is already a symptom of some bad data/metadata space
reservation, but here we need to focus on the error handling part.
For example, we have the following dirty page layout (4K sector size and
4K page size):
0 16K 32K
|/////|/////|/////|/////|/////|/////|/////|/////|
Where the range [0, 32K) is dirty and we need to write all the 8 pages
back.
When handling the first page 0, we go the following sequence:
- btrfs_run_delalloc_range() for range [0, 32k)
We enter cow_file_range() for [0, 32K)
- btrfs_reserve_extent() only returned a 16K data extent.
This can be caused by fragmentation, and it's already an indication
we're almost running of space.
Now we have the following layout:
0 16K 32K
|<----- Reserved ------>|/////|/////|/////|/////|
The range [0, 16K) has ordered extent allocated.
- btrfs_reserve_extent() returned -ENOSPC
We really run out of space. But since we have reserved space
for range [0, 16K) we need to clean them up.
But that cleanup for ordered extent only happens inside
btrfs_run_delalloc_range().
- btrfs_run_delalloc_range() cleanup the reserved ordered extent
By calling btrfs_mark_ordered_io_finished() for range [0, 32K).
It will locate the ordered extent [0, 16K) and mark it as IOERR.
Also since the ordered extent is only 16K, we're finishing the whole
ordered extent.
Thus we call btrfs_queue_ordered_fn() to queue to finish the ordered
extent.
But still, the ordered extent [0, 16K) is still in the
btrfs_inode::ordered_tree.
- extent_writepage() cleanup the ordered extent inside the folio
We call btrfs_mark_ordered_io_finished() for range [0, 4K).
Since the finished ordered extent [0, 16K) is not yet removed (racy,
depends on when btrfs_finish_one_ordered() is called), if
btrfs_mark_ordered_io_finished() is called before
btrfs_finish_one_ordered(), we will double account and trigger the
warning inside can_finish_ordered_extent().
So the root cause is, we're relying on btrfs_mark_ordered_io_finished()
to handle ranges which is already cleaned up.
Unfortunately the bug dates back to the early days when
btrfs_mark_ordered_io_finished() is introduced as a no-brain choice for
error paths, but such no-brain solution just hides all the race and make
us less cautious when handling errors.
[FIX]
Instead of relying on the btrfs_mark_ordered_io_finished() call to
cleanup the whole folio range, record the last successfully ran delalloc
range.
And combined with bio_ctrl->submit_bitmap to properly clean up any newly
created ordered extents.
Since we have cleaned up the ordered extents in range, we should not
rely on the btrfs_mark_ordered_io_finished() inside extent_writepage()
anymore.
By this, we ensure btrfs_mark_ordered_io_finished() is only called once
when writepage_delalloc() failed.
Cc: stable@xxxxxxxxxxxxxxx # 5.15+
Fixes: e65f152e4348 ("btrfs: refactor how we finish ordered extent io for endio functions")
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
fs/btrfs/extent_io.c | 37 ++++++++++++++++++++++++++++++++-----
1 file changed, 32 insertions(+), 5 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 9725ff7f274d..417c710c55ca 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1167,6 +1167,12 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
* last delalloc end.
*/
u64 last_delalloc_end = 0;
+ /*
+ * Save the last successfully ran delalloc range end (exclusive).
+ * This is for error handling to avoid ranges with ordered extent created
+ * but no IO will be submitted due to error.
+ */
+ u64 last_finished = page_start;
u64 delalloc_start = page_start;
u64 delalloc_end = page_end;
u64 delalloc_to_write = 0;
@@ -1235,11 +1241,19 @@ 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 = 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 = found_start + found_len;
} else {
/*
* We've hit an error during previous delalloc range,
@@ -1274,8 +1288,21 @@ 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 - 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;
@@ -1509,13 +1536,13 @@ 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(BTRFS_I(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.
--
2.47.1
