This is a note to let you know that I've just added the patch titled
btrfs: mark all dirty sectors as locked inside writepage_delalloc()
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-mark-all-dirty-sectors-as-locked-inside-writep.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 182a65d6168ea39c695e59c044242a703263b0ed
Author: Qu Wenruo <wqu@xxxxxxxx>
Date: Mon Sep 16 08:12:40 2024 +0930
btrfs: mark all dirty sectors as locked inside writepage_delalloc()
[ Upstream commit c96d0e3921419bd3e5d8a1f355970c8ae3047ef4 ]
Currently we only mark sectors as locked if there is a *NEW* delalloc
range for it.
But NEW delalloc range is not the same as dirty sectors we want to
submit, e.g:
0 32K 64K 96K 128K
| |////////||///////| |////|
120K
For above 64K page size case, writepage_delalloc() for page 0 will find
and lock the delalloc range [32K, 96K), which is beyond the page
boundary.
Then when writepage_delalloc() is called for the page 64K, since [64K,
96K) is already locked, only [120K, 128K) will be locked.
This means, although range [64K, 96K) is dirty and will be submitted
later by extent_writepage_io(), it will not be marked as locked.
This is fine for now, as we call btrfs_folio_end_writer_lock_bitmap() to
free every non-compressed sector, and compression is only allowed for
full page range.
But this is not safe for future sector perfect compression support, as
this can lead to double folio unlock:
Thread A | Thread B
---------------------------------------+--------------------------------
| submit_one_async_extent()
| |- extent_clear_unlock_delalloc()
extent_writepage() | |- btrfs_folio_end_writer_lock()
|- btrfs_folio_end_writer_lock_bitmap()| |- btrfs_subpage_end_and_test_writer()
| | | |- atomic_sub_and_test()
| | | /* Now the atomic value is 0 */
|- if (atomic_read() == 0) | |
|- folio_unlock() | |- folio_unlock()
The root cause is the above range [64K, 96K) is dirtied and should also
be locked but it isn't.
So to make everything more consistent and prepare for the incoming
sector perfect compression, mark all dirty sectors as locked.
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Stable-dep-of: 8bf334beb349 ("btrfs: fix double accounting race when extent_writepage_io() failed")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index ba34b92d48c2f..8222ae6f29af5 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1174,6 +1174,7 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
u64 delalloc_end = page_end;
u64 delalloc_to_write = 0;
int ret = 0;
+ int bit;
/* Save the dirty bitmap as our submission bitmap will be a subset of it. */
if (btrfs_is_subpage(fs_info, inode->vfs_inode.i_mapping)) {
@@ -1183,6 +1184,12 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
bio_ctrl->submit_bitmap = 1;
}
+ for_each_set_bit(bit, &bio_ctrl->submit_bitmap, fs_info->sectors_per_page) {
+ u64 start = page_start + (bit << fs_info->sectorsize_bits);
+
+ btrfs_folio_set_writer_lock(fs_info, folio, start, fs_info->sectorsize);
+ }
+
/* Lock all (subpage) delalloc ranges inside the folio first. */
while (delalloc_start < page_end) {
delalloc_end = page_end;
@@ -1193,9 +1200,6 @@ static noinline_for_stack int writepage_delalloc(struct btrfs_inode *inode,
}
set_delalloc_bitmap(folio, &delalloc_bitmap, delalloc_start,
min(delalloc_end, page_end) + 1 - delalloc_start);
- btrfs_folio_set_writer_lock(fs_info, folio, delalloc_start,
- min(delalloc_end, page_end) + 1 -
- delalloc_start);
last_delalloc_end = delalloc_end;
delalloc_start = delalloc_end + 1;
}
