[BUG]
With current subpage RW patchset, the following script can lead to
filesystem hang:
# mkfs.btrfs -f -s 4k $dev
# mount $dev -o nospace_cache $mnt
# fsstress -w -n 100 -p 1 -s 1608140256 -v -d $mnt
The file system will hang at wait_event() of
btrfs_start_ordered_extent().
[CAUSE]
The root cause is, btrfs_invalidatepage() is freeing page::private which
still has subpage dirty bit set.
The offending situation happens like this:
btrfs_fllocate()
|- btrfs_zero_range()
|- btrfs_punch_hole_lock_range()
|- truncate_pagecache_range()
|- btrfs_invalidatepage()
The involved range looks like:
0 32K 64K 96K 128K
|///////||//////|
| Range to drop |
For the [32K, 64K) range, since the offset is 32K, the page won't be
invalidated.
But for the [64K, 96K) range, the offset is 0, current
btrfs_invalidatepage() will call clear_page_extent_mapped() which will
detach page::private, making the subpage dirty bitmap being cleared.
This prevents later __extent_writepage_io() to locate any range to
write, thus no way to wake up the ordered extents.
[FIX]
To fix the problem this patch will:
- Only clear page status and detach page private when the full page
is invalidated
- Change how we handle unfinished ordered extent
If there is any ordered extent unfinished in the page range, we can't
call clear_extent_bit() with delete == true.
[REASON FOR RFC]
There is still uncertainty around the btrfs_releasepage() call.
1. Why we need btrfs_releasepage() call for non-full-page condition?
Other fs (aka. xfs) just exit without doing special handling if
invalidatepage() is called with part of the page.
Thus I didn't completely understand why btrfs_releasepage() here is
needed for non-full page call.
2. Why "if (offset)" is not causing problem for current code?
This existing if (offset) call can be skipped for cases like
offset == 0 length == 2K.
As MM layer can call invalidatepage() with unaligned offset/length,
for cases like truncate_inode_pages_range().
This will make btrfs_invalidatepage() to truncate the whole page when
we only need to zero part of the page.
Signed-off-by: Qu Wenruo <[email protected]>
---
fs/btrfs/inode.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index eb493fbb65f9..872c5309b4ca 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8180,7 +8180,7 @@ static void btrfs_invalidatepage(struct page *page,
unsigned int offset,
int inode_evicting = inode->vfs_inode.i_state & I_FREEING;
bool cleared_private2;
bool found_ordered = false;
- bool completed_ordered = false;
+ bool incompleted_ordered = false;
/*
* we have the page locked, so new writeback can't start,
@@ -8191,7 +8191,13 @@ static void btrfs_invalidatepage(struct page *page,
unsigned int offset,
*/
wait_on_page_writeback(page);
- if (offset) {
+ /*
+ * The range doesn't cover the full page, just let btrfs_releasepage()
to
+ * check if we can release the extent mapping.
+ * Any locked/pinned/logged extent map would prevent us freeing the
+ * extent mapping.
+ */
+ if (!(offset == 0 && length == PAGE_SIZE)) {
btrfs_releasepage(page, GFP_NOFS);
return;
}
@@ -8208,9 +8214,10 @@ static void btrfs_invalidatepage(struct page *page,
unsigned int offset,
end = min(page_end,
ordered->file_offset + ordered->num_bytes - 1);
/*
- * IO on this page will never be started, so we need to account
- * for any ordered extents now. Don't clear EXTENT_DELALLOC_NEW
- * here, must leave that up for the ordered extent completion.
+ * IO on this ordered extent will never be started, so we need
+ * to account for any ordered extents now. Don't clear
+ * EXTENT_DELALLOC_NEW here, must leave that up for the
+ * ordered extent completion.
*/
if (!inode_evicting)
clear_extent_bit(tree, start, end,
@@ -8234,7 +8241,8 @@ static void btrfs_invalidatepage(struct page *page,
unsigned int offset,
start,
end - start + 1, 1))
{
btrfs_finish_ordered_io(ordered);
- completed_ordered = true;
+ } else {
+ incompleted_ordered = true;
}
}
@@ -8276,7 +8284,7 @@ static void btrfs_invalidatepage(struct page *page,
unsigned int offset,
* is cleared if we don't delete, otherwise it can lead to
* corruptions if the i_size is extented later.
*/
- if (found_ordered && !completed_ordered)
+ if (found_ordered && incompleted_ordered)
delete = false;
clear_extent_bit(tree, page_start, page_end, EXTENT_LOCKED |
EXTENT_DELALLOC | EXTENT_UPTODATE |
@@ -8286,6 +8294,7 @@ static void btrfs_invalidatepage(struct page *page,
unsigned int offset,
__btrfs_releasepage(page, GFP_NOFS);
}
+ ClearPagePrivate2(page);
ClearPageChecked(page);
clear_page_extent_mapped(page);
}
--
2.29.2
