[BUG]
With current subpage RW support, the following script can hang the fs on
with 64K page size.
# mkfs.btrfs -f -s 4k $dev
# mount $dev -o nospace_cache $mnt
# fsstress -w -n 50 -p 1 -s 1607749395 -d $mnt
The kernel will do an infinite loop in btrfs_punch_hole_lock_range().
[CAUSE]
In btrfs_punch_hole_lock_range() we:
- Truncate page cache range
- Lock extent io tree
- Wait any ordered extents in the range.
We exit the loop until we meet all the following conditions:
- No ordered extent in the lock range
- No page is in the lock range
The latter condition has a pitfall, it only works for sector size ==
PAGE_SIZE case.
While can't handle the following subpage case:
0 32K 64K 96K 128K
| |///////||//////| ||
lockstart=32K
lockend=96K - 1
In this case, although the range cross 2 pages,
truncate_pagecache_range() will invalidate no page at all, but only zero
the [32K, 96K) range of the two pages.
Thus filemap_range_has_page(32K, 96K-1) will always return true, thus we
will never meet the loop exit condition.
[FIX]
Fix the problem by doing page alignment for the lock range.
Function filemap_range_has_page() has already handled lend < lstart
case, we only need to round up @lockstart, and round_down @lockend for
truncate_pagecache_range().
This modification should not change any thing for sector size ==
PAGE_SIZE case, as in that case our range is already page aligned.
Signed-off-by: Qu Wenruo <w...@suse.com>
---
fs/btrfs/file.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 8f71699fdd18..45ec3f5ef839 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2471,6 +2471,16 @@ static int btrfs_punch_hole_lock_range(struct inode
*inode,
const u64 lockend,
struct extent_state **cached_state)
{
+ /*
+ * For subpage case, if the range is not at page boundary, we could
+ * have pages at the leading/tailing part of the range.
+ * This could lead to dead loop since filemap_range_has_page()
+ * will always return true.
+ * So here we need to do extra page alignment for
+ * filemap_range_has_page().
+ */
+ u64 page_lockstart = round_up(lockstart, PAGE_SIZE);
+ u64 page_lockend = round_down(lockend + 1, PAGE_SIZE) - 1;
while (1) {
struct btrfs_ordered_extent *ordered;
int ret;
@@ -2491,7 +2501,7 @@ static int btrfs_punch_hole_lock_range(struct inode
*inode,
(ordered->file_offset + ordered->num_bytes <= lockstart ||
ordered->file_offset > lockend)) &&
!filemap_range_has_page(inode->i_mapping,
- lockstart, lockend)) {
+ page_lockstart, page_lockend)) {
if (ordered)
btrfs_put_ordered_extent(ordered);
break;
--
2.31.1
