From: Qu Wenruo Date: Mon, 26 Jul 2021 06:34:58 +0000 (+0800) Subject: btrfs: subpage: fix writeback which does not have ordered extent X-Git-Tag: accepted/tizen/unified/20230118.172025~6109^2~92 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=cc1d0d93d55ac12e7faee9acfcd7c28c8b86cf89;p=platform%2Fkernel%2Flinux-rpi.git btrfs: subpage: fix writeback which does not have ordered extent [BUG] When running fsstress with subpage RW support, there are random BUG_ON()s triggered with the following trace: kernel BUG at fs/btrfs/file-item.c:667! Internal error: Oops - BUG: 0 [#1] SMP CPU: 1 PID: 3486 Comm: kworker/u13:2 5.11.0-rc4-custom+ #43 Hardware name: Radxa ROCK Pi 4B (DT) Workqueue: btrfs-worker-high btrfs_work_helper [btrfs] pstate: 60000005 (nZCv daif -PAN -UAO -TCO BTYPE=--) pc : btrfs_csum_one_bio+0x420/0x4e0 [btrfs] lr : btrfs_csum_one_bio+0x400/0x4e0 [btrfs] Call trace: btrfs_csum_one_bio+0x420/0x4e0 [btrfs] btrfs_submit_bio_start+0x20/0x30 [btrfs] run_one_async_start+0x28/0x44 [btrfs] btrfs_work_helper+0x128/0x1b4 [btrfs] process_one_work+0x22c/0x430 worker_thread+0x70/0x3a0 kthread+0x13c/0x140 ret_from_fork+0x10/0x30 [CAUSE] Above BUG_ON() means there is some bio range which doesn't have ordered extent, which indeed is worth a BUG_ON(). Unlike regular sectorsize == PAGE_SIZE case, in subpage we have extra subpage dirty bitmap to record which range is dirty and should be written back. This means, if we submit bio for a subpage range, we do not only need to clear page dirty, but also need to clear subpage dirty bits. In __extent_writepage_io(), we will call btrfs_page_clear_dirty() for any range we submit a bio. But there is loophole, if we hit a range which is beyond i_size, we just call btrfs_writepage_endio_finish_ordered() to finish the ordered io, then break out, without clearing the subpage dirty. This means, if we hit above branch, the subpage dirty bits are still there, if other range of the page get dirtied and we need to writeback that page again, we will submit bio for the old range, leaving a wild bio range which doesn't have ordered extent. [FIX] Fix it by always calling btrfs_page_clear_dirty() in __extent_writepage_io(). Also to avoid such problem from happening again, add a new assert, btrfs_page_assert_not_dirty(), to make sure both page dirty and subpage dirty bits are cleared before exiting __extent_writepage_io(). Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 4ee1066..e1a464f 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -3864,6 +3864,15 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, if (cur >= i_size) { btrfs_writepage_endio_finish_ordered(inode, page, cur, end, true); + /* + * This range is beyond i_size, thus we don't need to + * bother writing back. + * But we still need to clear the dirty subpage bit, or + * the next time the page gets dirtied, we will try to + * writeback the sectors with subpage dirty bits, + * causing writeback without ordered extent. + */ + btrfs_page_clear_dirty(fs_info, page, cur, end + 1 - cur); break; } @@ -3914,6 +3923,7 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, else btrfs_writepage_endio_finish_ordered(inode, page, cur, cur + iosize - 1, true); + btrfs_page_clear_dirty(fs_info, page, cur, iosize); cur += iosize; continue; } @@ -3949,6 +3959,12 @@ static noinline_for_stack int __extent_writepage_io(struct btrfs_inode *inode, cur += iosize; nr++; } + /* + * If we finish without problem, we should not only clear page dirty, + * but also empty subpage dirty bits + */ + if (!ret) + btrfs_page_assert_not_dirty(fs_info, page); *nr_ret = nr; return ret; } diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c index 640bcd2..3c31184 100644 --- a/fs/btrfs/subpage.c +++ b/fs/btrfs/subpage.c @@ -559,3 +559,23 @@ IMPLEMENT_BTRFS_PAGE_OPS(writeback, set_page_writeback, end_page_writeback, PageWriteback); IMPLEMENT_BTRFS_PAGE_OPS(ordered, SetPageOrdered, ClearPageOrdered, PageOrdered); + +/* + * Make sure not only the page dirty bit is cleared, but also subpage dirty bit + * is cleared. + */ +void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info, + struct page *page) +{ + struct btrfs_subpage *subpage = (struct btrfs_subpage *)page->private; + + if (!IS_ENABLED(CONFIG_BTRFS_ASSERT)) + return; + + ASSERT(!PageDirty(page)); + if (fs_info->sectorsize == PAGE_SIZE) + return; + + ASSERT(PagePrivate(page) && page->private); + ASSERT(subpage->dirty_bitmap == 0); +} diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h index 4d7aca8..0120948 100644 --- a/fs/btrfs/subpage.h +++ b/fs/btrfs/subpage.h @@ -126,4 +126,7 @@ DECLARE_BTRFS_SUBPAGE_OPS(ordered); bool btrfs_subpage_clear_and_test_dirty(const struct btrfs_fs_info *fs_info, struct page *page, u64 start, u32 len); +void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info, + struct page *page); + #endif