On Fri, Mar 25, 2022 at 04:14:28PM -0400, Rik van Riel wrote:
> In some cases it appears the invalidation of a hwpoisoned page
> fails because the page is still mapped in another process. This
> can cause a program to be continuously restarted and die when
> it page faults on the page that was not invalidated. Avoid that
> problem by unmapping the hwpoisoned page when we find it.
>
> Another issue is that sometimes we end up oopsing in finish_fault,
> if the code tries to do something with the now-NULL vmf->page.
> I did not hit this error when submitting the previous patch because
> there are several opportunities for alloc_set_pte to bail out before
> accessing vmf->page, and that apparently happened on those systems,
> and most of the time on other systems, too.
>
> However, across several million systems that error does occur a
> handful of times a day. It can be avoided by returning VM_FAULT_NOPAGE
> which will cause do_read_fault to return before calling finish_fault.
>
> Fixes: e53ac7374e64 ("mm: invalidate hwpoison page cache page in fault path")
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> mm/memory.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index be44d0b36b18..76e3af9639d9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3918,14 +3918,18 @@ static vm_fault_t __do_fault(struct vm_fault *vmf)
> return ret;
>
> if (unlikely(PageHWPoison(vmf->page))) {
> + struct page *page = vmf->page;
> vm_fault_t poisonret = VM_FAULT_HWPOISON;
> if (ret & VM_FAULT_LOCKED) {
> + if (page_mapped(page))
> + unmap_mapping_pages(page_mapping(page),
> + page->index, 1, false);
> /* Retry if a clean page was removed from the cache. */
> - if (invalidate_inode_page(vmf->page))
> - poisonret = 0;
> - unlock_page(vmf->page);
> + if (invalidate_inode_page(page))
> + poisonret = VM_FAULT_NOPAGE;
What is the effect of returning VM_FAULT_NOPAGE?
I take that we are cool because the pte has been installed and points to
a new page? (I could not find where that is being done).
--
Oscar Salvador
SUSE Labs
