xfs: cancel dirty pages on invalidation (793d7dbe) · Commits · 戴 / test

Recently we've had warnings arise from the vm handing us pages without bufferheads attached to them. This should not ever occur in XFS, but we don't defend against it properly if it does. The only place where we remove bufferheads from a page is in xfs_vm_releasepage(), but we can't tell the difference here between "page is dirty so don't release" and "page is dirty but is being invalidated so release it". In some places that are invalidating pages ask for pages to be released and follow up afterward calling ->releasepage by checking whether the page was dirty and then aborting the invalidation. This is a possible vector for releasing buffers from a page but then leaving it in the mapping, so we really do need to avoid dirty pages in xfs_vm_releasepage(). To differentiate between invalidated pages and normal pages, we need to clear the page dirty flag when invalidating the pages. This can be done through xfs_vm_invalidatepage(), and will result xfs_vm_releasepage() seeing the page as clean which matches the bufferhead state on the page after calling block_invalidatepage(). Hence we can re-add the page dirty check in xfs_vm_releasepage to catch the case where we might be releasing a page that is actually dirty and so should not have the bufferheads on it removed. This will remove one possible vector of "dirty page with no bufferheads" and so help narrow down the search for the root cause of that problem. Signed-Off-By:

Dave Chinner <dchinner@redhat.com> Reviewed-by:

Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by:

Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_aops.c

+22 −12

Original line number	Diff line number	Diff line
		@@ -735,6 +735,14 @@ xfs_vm_invalidatepage(
		{
		trace_xfs_invalidatepage(page->mapping->host, page, offset,
		length);

		/*
		* If we are invalidating the entire page, clear the dirty state from it
		* so that we can check for attempts to release dirty cached pages in
		* xfs_vm_releasepage().
		*/
		if (offset == 0 && length >= PAGE_SIZE)
		cancel_dirty_page(page);
		block_invalidatepage(page, offset, length);
		}

		@@ -1190,25 +1198,27 @@ xfs_vm_releasepage(
		* mm accommodates an old ext3 case where clean pages might not have had
		* the dirty bit cleared. Thus, it can send actual dirty pages to
		* ->releasepage() via shrink_active_list(). Conversely,
		* block_invalidatepage() can send pages that are still marked dirty
		* but otherwise have invalidated buffers.
		* block_invalidatepage() can send pages that are still marked dirty but
		* otherwise have invalidated buffers.
		*
		* We want to release the latter to avoid unnecessary buildup of the
		* LRU, skip the former and warn if we've left any lingering
		* delalloc/unwritten buffers on clean pages. Skip pages with delalloc
		* or unwritten buffers and warn if the page is not dirty. Otherwise
		* try to release the buffers.
		* LRU, so xfs_vm_invalidatepage() clears the page dirty flag on pages
		* that are entirely invalidated and need to be released. Hence the
		* only time we should get dirty pages here is through
		* shrink_active_list() and so we can simply skip those now.
		*
		* warn if we've left any lingering delalloc/unwritten buffers on clean
		* or invalidated pages we are about to release.
		*/
		if (PageDirty(page))
		return 0;

		xfs_count_page_state(page, &delalloc, &unwritten);

		if (delalloc) {
		WARN_ON_ONCE(!PageDirty(page));
		if (WARN_ON_ONCE(delalloc))
		return 0;
		}
		if (unwritten) {
		WARN_ON_ONCE(!PageDirty(page));
		if (WARN_ON_ONCE(unwritten))
		return 0;
		}

		return try_to_free_buffers(page);
		}

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