[PATCH v2 20/26] btrfs: make extent_write_locked_range() to be subpage compatible

Qu Wenruo
2021-08-29T05:25:29Z

There are two sites are not subpage compatible yet for
extent_write_locked_range():

- How @nr_pages are calculated
For subpage we can have the following range with 64K page size:

0 32K 64K 96K 128K
| |////|/////| |

In that case, although 96K - 32K == 64K, thus it looks like one page
is enough, but the range spans across two pages, not one.

Fix it by doing proper round_up() and round_down() to calculate
@nr_pages.

Also add some extra ASSERT()s to ensure the range passed in is already
aligned.

- How the page end is calculated
Currently we just use cur + PAGE_SIZE - 1 to calculate the page end.

Which can't handle above range layout, and will trigger ASSERT() in
btrfs_writepage_endio_finish_ordered(), as the range is no longer
covered by the page range.

Fix it by take page end into consideration.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
fs/btrfs/extent_io.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f6f4c069cf06..077856bf15d0 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5096,15 +5096,14 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
struct address_space *mapping = inode->i_mapping;
struct page *page;
u64 cur = start;
- unsigned long nr_pages = (end - start + PAGE_SIZE) >>
- PAGE_SHIFT;
+ unsigned long nr_pages;
+ const u32 sectorsize = btrfs_sb(inode->i_sb)->sectorsize;
struct extent_page_data epd = {
.bio_ctrl = { 0 },
.extent_locked = 1,
.sync_io = 1,
};
struct writeback_control wbc_writepages = {
- .nr_to_write = nr_pages * 2,
.sync_mode = WB_SYNC_ALL,
.range_start = start,
.range_end = end + 1,
@@ -5113,14 +5112,24 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
.no_cgroup_owner = 1,
};

+ ASSERT(IS_ALIGNED(start, sectorsize) &&
+ IS_ALIGNED(end + 1, sectorsize));
+ nr_pages = (round_up(end, PAGE_SIZE) - round_down(start, PAGE_SIZE)) >>
+ PAGE_SHIFT;
+ wbc_writepages.nr_to_write = nr_pages * 2;
+
wbc_attach_fdatawrite_inode(&wbc_writepages, inode);
while (cur <= end) {
+ u64 cur_end = min(round_down(cur, PAGE_SIZE) + PAGE_SIZE - 1,
+ end);
+
page = find_get_page(mapping, cur >> PAGE_SHIFT);
/*
* All pages in the range are locked since
* btrfs_run_delalloc_range(), thus there is no way to clear
* the page dirty flag.
*/
+ ASSERT(PageLocked(page));
ASSERT(PageDirty(page));
clear_page_dirty_for_io(page);
ret = __extent_writepage(page, &wbc_writepages, &epd);
@@ -5130,7 +5139,7 @@ int extent_write_locked_range(struct inode *inode, u64 start, u64 end)
first_error = ret;
}
put_page(page);
- cur += PAGE_SIZE;
+ cur = cur_end + 1;
}

if (!found_error)
--
2.32.0