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iomap: support partial page discard on writeback block mapping failure

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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 <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Brian Foster
2020-10-29 14:30:48 -07:00
committed by Darrick J. Wong
parent 869ae85dae
commit 763e4cdc0f
3 changed files with 17 additions and 14 deletions
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14
fs/xfs/xfs_aops.c
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@@ -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 = {