btrfs: subpage: make extent_write_locked_range() compatible

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 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 the 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 taking page end into consideration.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a010a40..655e78a 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5086,15 +5086,14 @@ 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,
@@ -5103,14 +5102,22 @@ 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);
@@ -5120,7 +5127,7 @@ 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)