Re: Checking page_count(page) in invalidate_complete_page

Chuck Lever
2006-09-29T21:48:23Z

Andrew Morton wrote:
> buggerit, let's do this. It'll fix NFS, yes?

It looks right to me. I'll discuss a patch with Trond that adds a
warning in nfs_revalidate_mapping() and perhaps a performance counter to
see how many times we hit this in practice.

> From: Andrew Morton <akpm@osdl.org>
>
> The recent fix to invalidate_inode_pages() (git commit 016eb4a) managed to
> unfix invalidate_inode_pages2().
>
> The problem is that various bits of code in the kernel can take transient refs
> on pages: the page scanner will do this when inspecting a batch of pages, and
> the lru_cache_add() batching pagevecs also hold a ref.
>
> Net result is transient failures in invalidate_inode_pages2(). This affects
> NFS directory invalidation (observed) and presumably also block-backed
> direct-io (not yet reported).
>
> Fix it by reverting invalidate_inode_pages2() back to the old version which
> ignores the page refcounts.
>
> We may come up with something more clever later, but for now we need a 2.6.18
> fix for NFS.
>
> Cc: Chuck Lever <cel@citi.umich.edu>
> Cc: Nick Piggin <nickpiggin@yahoo.com.au>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: <stable@kernel.org>
> Signed-off-by: Andrew Morton <akpm@osdl.org>
> ---
>
> mm/truncate.c | 34 ++++++++++++++++++++++++++++++++--
> 1 files changed, 32 insertions(+), 2 deletions(-)
>
> diff -puN mm/truncate.c~invalidate_inode_pages2-ignore-page-refcounts mm/truncate.c
> --- a/mm/truncate.c~invalidate_inode_pages2-ignore-page-refcounts
> +++ a/mm/truncate.c
> @@ -261,9 +261,39 @@ unsigned long invalidate_inode_pages(str
> {
> return invalidate_mapping_pages(mapping, 0, ~0UL);
> }
> -
> EXPORT_SYMBOL(invalidate_inode_pages);
>
> +/*
> + * This is like invalidate_complete_page(), except it ignores the page's
> + * refcount. We do this because invalidate_indoe_pages2() needs stronger
> + * invalidation guarantees, and cannot afford to leave pages behind because
> + * shrink_list() has a temp ref on them, or because they're transiently sitting
> + * in the lru_cache_add() pagevecs.
> + */
> +static int
> +invalidate_complete_page2(struct address_space *mapping, struct page *page)
> +{
> + if (page->mapping != mapping)
> + return 0;
> +
> + if (PagePrivate(page) && !try_to_release_page(page, 0))
> + return 0;
> +
> + write_lock_irq(&mapping->tree_lock);
> + if (PageDirty(page))
> + goto failed;
> +
> + BUG_ON(PagePrivate(page));
> + __remove_from_page_cache(page);
> + write_unlock_irq(&mapping->tree_lock);
> + ClearPageUptodate(page);
> + page_cache_release(page); /* pagecache ref */
> + return 1;
> +failed:
> + write_unlock_irq(&mapping->tree_lock);
> + return 0;
> +}
> +
> /**
> * invalidate_inode_pages2_range - remove range of pages from an address_space
> * @mapping: the address_space
> @@ -330,7 +360,7 @@ int invalidate_inode_pages2_range(struct
> }
> }
> was_dirty = test_clear_page_dirty(page);
> - if (!invalidate_complete_page(mapping, page)) {
> + if (!invalidate_complete_page2(mapping, page)) {
> if (was_dirty)
> set_page_dirty(page);
> ret = -EIO;
> _