From 763e4cdc0f6d5cea45c896fef67f7be4bdefcca7 Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Thu, 29 Oct 2020 14:30:48 -0700 Subject: iomap: support partial page discard on writeback block mapping failure iomap writeback mapping failure only calls into ->discard_page() if the current page has not been added to the ioend. Accordingly, the XFS callback assumes a full page discard and invalidation. This is problematic for sub-page block size filesystems where some portion of a page might have been mapped successfully before a failure to map a delalloc block occurs. ->discard_page() is not called in that error scenario and the bio is explicitly failed by iomap via the error return from ->prepare_ioend(). As a result, the filesystem leaks delalloc blocks and corrupts the filesystem block counters. Since XFS is the only user of ->discard_page(), tweak the semantics to invoke the callback unconditionally on mapping errors and provide the file offset that failed to map. Update xfs_discard_page() to discard the corresponding portion of the file and pass the range along to iomap_invalidatepage(). The latter already properly handles both full and sub-page scenarios by not changing any iomap or page state on sub-page invalidations. Signed-off-by: Brian Foster Reviewed-by: Christoph Hellwig Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong --- fs/xfs/xfs_aops.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) (limited to 'fs/xfs/xfs_aops.c') diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index 55d126d4e096..5bf37afae5e9 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -527,13 +527,15 @@ xfs_prepare_ioend( */ static void xfs_discard_page( - struct page *page) + struct page *page, + loff_t fileoff) { struct inode *inode = page->mapping->host; struct xfs_inode *ip = XFS_I(inode); struct xfs_mount *mp = ip->i_mount; - loff_t offset = page_offset(page); - xfs_fileoff_t start_fsb = XFS_B_TO_FSBT(mp, offset); + unsigned int pageoff = offset_in_page(fileoff); + xfs_fileoff_t start_fsb = XFS_B_TO_FSBT(mp, fileoff); + xfs_fileoff_t pageoff_fsb = XFS_B_TO_FSBT(mp, pageoff); int error; if (XFS_FORCED_SHUTDOWN(mp)) @@ -541,14 +543,14 @@ xfs_discard_page( xfs_alert_ratelimited(mp, "page discard on page "PTR_FMT", inode 0x%llx, offset %llu.", - page, ip->i_ino, offset); + page, ip->i_ino, fileoff); error = xfs_bmap_punch_delalloc_range(ip, start_fsb, - i_blocks_per_page(inode, page)); + i_blocks_per_page(inode, page) - pageoff_fsb); if (error && !XFS_FORCED_SHUTDOWN(mp)) xfs_alert(mp, "page discard unable to remove delalloc mapping."); out_invalidate: - iomap_invalidatepage(page, 0, PAGE_SIZE); + iomap_invalidatepage(page, pageoff, PAGE_SIZE - pageoff); } static const struct iomap_writeback_ops xfs_writeback_ops = { -- cgit From c2f09217a4305478c55adc9a98692488dd19cd32 Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Mon, 2 Nov 2020 17:14:06 -0800 Subject: xfs: fix missing CoW blocks writeback conversion retry In commit 7588cbeec6df, we tried to fix a race stemming from the lack of coordination between higher level code that wants to allocate and remap CoW fork extents into the data fork. Christoph cites as examples the always_cow mode, and a directio write completion racing with writeback. According to the comments before the goto retry, we want to restart the lookup to catch the extent in the data fork, but we don't actually reset whichfork or cow_fsb, which means the second try executes using stale information. Up until now I think we've gotten lucky that either there's something left in the CoW fork to cause cow_fsb to be reset, or either data/cow fork sequence numbers have advanced enough to force a fresh lookup from the data fork. However, if we reach the retry with an empty stable CoW fork and a stable data fork, neither of those things happens. The retry foolishly re-calls xfs_convert_blocks on the CoW fork which fails again. This time, we toss the write. I've recently been working on extending reflink to the realtime device. When the realtime extent size is larger than a single block, we have to force the page cache to CoW the entire rt extent if a write (or fallocate) are not aligned with the rt extent size. The strategy I've chosen to deal with this is derived from Dave's blocksize > pagesize series: dirtying around the write range, and ensuring that writeback always starts mapping on an rt extent boundary. This has brought this race front and center, since generic/522 blows up immediately. However, I'm pretty sure this is a bug outright, independent of that. Fixes: 7588cbeec6df ("xfs: retry COW fork delalloc conversion when no extent was found") Signed-off-by: Darrick J. Wong Reviewed-by: Christoph Hellwig --- fs/xfs/xfs_aops.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'fs/xfs/xfs_aops.c') diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index 5bf37afae5e9..4304c6416fbb 100644 --- a/fs/xfs/xfs_aops.c +++ b/fs/xfs/xfs_aops.c @@ -346,8 +346,8 @@ xfs_map_blocks( ssize_t count = i_blocksize(inode); xfs_fileoff_t offset_fsb = XFS_B_TO_FSBT(mp, offset); xfs_fileoff_t end_fsb = XFS_B_TO_FSB(mp, offset + count); - xfs_fileoff_t cow_fsb = NULLFILEOFF; - int whichfork = XFS_DATA_FORK; + xfs_fileoff_t cow_fsb; + int whichfork; struct xfs_bmbt_irec imap; struct xfs_iext_cursor icur; int retries = 0; @@ -381,6 +381,8 @@ xfs_map_blocks( * landed in a hole and we skip the block. */ retry: + cow_fsb = NULLFILEOFF; + whichfork = XFS_DATA_FORK; xfs_ilock(ip, XFS_ILOCK_SHARED); ASSERT(ip->i_df.if_format != XFS_DINODE_FMT_BTREE || (ip->i_df.if_flags & XFS_IFEXTENTS)); -- cgit