From e55a0de185726ca43e8a31d363ad73c4f0a6770b Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Mon, 27 Sep 2021 15:22:05 +0800 Subject: [PATCH] btrfs: rework page locking in __extent_writepage() Pages passed to __extent_writepage() are always locked, but they may be locked by different functions. There are two types of locked page for __extent_writepage(): - Page locked by plain lock_page() It should not have any subpage::writers count. Can be unlocked by unlock_page(). This is the most common locked page for __extent_writepage() called inside extent_write_cache_pages() or extent_write_full_page(). Rarer cases include the @locked_page from extent_write_locked_range(). - Page locked by lock_delalloc_pages() There is only one caller, all pages except @locked_page for extent_write_locked_range(). In this case, we have to call subpage helper to handle the case. So here we introduce a helper, btrfs_page_unlock_writer(), to allow __extent_writepage() to unlock different locked pages. And since for all other callers of __extent_writepage() their pages are ensured to be locked by lock_page(), also add an extra check for epd::extent_locked to unlock such pages directly. Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 15 ++++++++++++++- fs/btrfs/subpage.c | 43 +++++++++++++++++++++++++++++++++++++++++++ fs/btrfs/subpage.h | 2 ++ 3 files changed, 59 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 655e78ae376e..18ef234fe3dc 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4051,6 +4051,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, struct extent_page_data *epd) { struct inode *inode = page->mapping->host; + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); const u64 page_start = page_offset(page); const u64 page_end = page_start + PAGE_SIZE - 1; int ret; @@ -4138,7 +4139,19 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc, */ if (PageError(page)) end_extent_writepage(page, ret, page_start, page_end); - unlock_page(page); + if (epd->extent_locked) { + /* + * If epd->extent_locked, it's from extent_write_locked_range(), + * the page can either be locked by lock_page() or + * process_one_page(). + * Let btrfs_page_unlock_writer() handle both cases. + */ + ASSERT(wbc); + btrfs_page_unlock_writer(fs_info, page, wbc->range_start, + wbc->range_end + 1 - wbc->range_start); + } else { + unlock_page(page); + } ASSERT(ret <= 0); return ret; } diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c index ed9936cdd267..265b6aa1c662 100644 --- a/fs/btrfs/subpage.c +++ b/fs/btrfs/subpage.c @@ -690,3 +690,46 @@ void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info, ASSERT(PagePrivate(page) && page->private); ASSERT(subpage_test_bitmap_all_zero(fs_info, subpage, dirty)); } + +/* + * Handle different locked pages with different page sizes: + * + * - Page locked by plain lock_page() + * It should not have any subpage::writers count. + * Can be unlocked by unlock_page(). + * This is the most common locked page for __extent_writepage() called + * inside extent_write_cache_pages() or extent_write_full_page(). + * Rarer cases include the @locked_page from extent_write_locked_range(). + * + * - Page locked by lock_delalloc_pages() + * There is only one caller, all pages except @locked_page for + * extent_write_locked_range(). + * In this case, we have to call subpage helper to handle the case. + */ +void btrfs_page_unlock_writer(struct btrfs_fs_info *fs_info, struct page *page, + u64 start, u32 len) +{ + struct btrfs_subpage *subpage; + + ASSERT(PageLocked(page)); + /* For regular page size case, we just unlock the page */ + if (fs_info->sectorsize == PAGE_SIZE) + return unlock_page(page); + + ASSERT(PagePrivate(page) && page->private); + subpage = (struct btrfs_subpage *)page->private; + + /* + * For subpage case, there are two types of locked page. With or + * without writers number. + * + * Since we own the page lock, no one else could touch subpage::writers + * and we are safe to do several atomic operations without spinlock. + */ + if (atomic_read(&subpage->writers)) + /* No writers, locked by plain lock_page() */ + return unlock_page(page); + + /* Have writers, use proper subpage helper to end it */ + btrfs_page_end_writer_lock(fs_info, page, start, len); +} diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h index 46224f959c34..7accb5c40d33 100644 --- a/fs/btrfs/subpage.h +++ b/fs/btrfs/subpage.h @@ -150,5 +150,7 @@ bool btrfs_subpage_clear_and_test_dirty(const struct btrfs_fs_info *fs_info, void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info, struct page *page); +void btrfs_page_unlock_writer(struct btrfs_fs_info *fs_info, struct page *page, + u64 start, u32 len); #endif -- GitLab