Commit 416d85ed authored by Mike Kravetz's avatar Mike Kravetz Committed by Linus Torvalds
Browse files

hugetlb: simplify prep_compound_gigantic_page ref count racing code 

Code in prep_compound_gigantic_page waits for a rcu grace period if it
notices a temporarily inflated ref count on a tail page.  This was due to
the identified potential race with speculative page cache references which
could only last for a rcu grace period.  This is overly complicated as
this situation is VERY unlikely to ever happen.  Instead, just quickly
return an error.

Also, only print a warning in prep_compound_gigantic_page instead of
multiple callers.

Link: https://lkml.kernel.org/r/20210809184832.18342-2-mike.kravetz@oracle.com


Signed-off-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f87060d3

mm/hugetlb.c

+7 −10
Original line number Diff line number Diff line
@@ -1657,15 +1657,13 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order) 
		 * cache adding could take a ref on a 'to be' tail page.

		 * We need to respect any increased ref count, and only set

		 * the ref count to zero if count is currently 1.  If count

		 * is not 1, we call synchronize_rcu in the hope that a rcu

		 * grace period will cause ref count to drop and then retry.

		 * If count is still inflated on retry we return an error and

		 * must discard the pages.

		 * is not 1, we return an error.  An error return indicates

		 * the set of pages can not be converted to a gigantic page.

		 * The caller who allocated the pages should then discard the

		 * pages using the appropriate free interface.

		 */

		if (!page_ref_freeze(p, 1)) {

			pr_info("HugeTLB unexpected inflated ref count on freshly allocated page\n");

			synchronize_rcu();

			if (!page_ref_freeze(p, 1))

			pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");

			goto out_error;

		}

		set_page_count(p, 0);
@@ -1830,7 +1828,6 @@ static struct page *alloc_fresh_huge_page(struct hstate *h, 
				retry = true;

				goto retry;

			}

			pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");

			return NULL;

		}

	}
@@ -2828,8 +2825,8 @@ static void __init gather_bootmem_prealloc(void) 
			prep_new_huge_page(h, page, page_to_nid(page));

			put_page(page); /* add to the hugepage allocator */

		} else {

			/* VERY unlikely inflated ref count on a tail page */

			free_gigantic_page(page, huge_page_order(h));

			pr_warn("HugeTLB page can not be used due to unexpected inflated ref count\n");

		}



		/*