On Fri, 13 Jul 2018 12:26:06 +0900 Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> wrote:
> A process can be killed with SIGBUS(BUS_MCEERR_AR) when it tries to
> allocate a page that was just freed on the way of soft-offline.
> This is undesirable because soft-offline (which is about corrected error)
> is less aggressive than hard-offline (which is about uncorrected error),
> and we can make soft-offline fail and keep using the page for good reason
> like "system is busy."
>
> Two main changes of this patch are:
>
> - setting migrate type of the target page to MIGRATE_ISOLATE. As done
> in free_unref_page_commit(), this makes kernel bypass pcplist when
> freeing the page. So we can assume that the page is in freelist just
> after put_page() returns,
>
> - setting PG_hwpoison on free page under zone->lock which protects
> freelists, so this allows us to avoid setting PG_hwpoison on a page
> that is decided to be allocated soon.
>
>
> ...
>
> +
> +#ifdef CONFIG_MEMORY_FAILURE
> +/*
> + * Set PG_hwpoison flag if a given page is confirmed to be a free page
> + * within zone lock, which prevents the race against page allocation.
> + */
I think this is clearer?
--- a/mm/page_alloc.c~mm-soft-offline-close-the-race-against-page-allocation-fix
+++ a/mm/page_alloc.c
@@ -8039,8 +8039,9 @@ bool is_free_buddy_page(struct page *pag
#ifdef CONFIG_MEMORY_FAILURE
/*
- * Set PG_hwpoison flag if a given page is confirmed to be a free page
- * within zone lock, which prevents the race against page allocation.
+ * Set PG_hwpoison flag if a given page is confirmed to be a free page. This
+ * test is performed under the zone lock to prevent a race against page
+ * allocation.
*/
bool set_hwpoison_free_buddy_page(struct page *page)
{
> +bool set_hwpoison_free_buddy_page(struct page *page)
> +{
> + struct zone *zone = page_zone(page);
> + unsigned long pfn = page_to_pfn(page);
> + unsigned long flags;
> + unsigned int order;
> + bool hwpoisoned = false;
> +
> + spin_lock_irqsave(&zone->lock, flags);
> + for (order = 0; order < MAX_ORDER; order++) {
> + struct page *page_head = page - (pfn & ((1 << order) - 1));
> +
> + if (PageBuddy(page_head) && page_order(page_head) >= order) {
> + if (!TestSetPageHWPoison(page))
> + hwpoisoned = true;
> + break;
> + }
> + }
> + spin_unlock_irqrestore(&zone->lock, flags);
> +
> + return hwpoisoned;
> +}
> +#endif
