The patch titled
Subject: hugetlb: remove prep_compound_huge_page cleanup
has been added to the -mm tree. Its filename is
hugetlb-remove-prep_compound_huge_page-cleanup.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/hugetlb-remove-prep_compound_huge_page-cleanup.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/hugetlb-remove-prep_compound_huge_page-cleanup.patch
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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Subject: hugetlb: remove prep_compound_huge_page cleanup
Patch series "Fix prep_compound_gigantic_page ref count adjustment".
These patches address the possible race between
prep_compound_gigantic_page and __page_cache_add_speculative as described
by Jann Horn in [1].
The first patch simply removes the unnecessary/obsolete helper routine
prep_compound_huge_page to make the actual fix a little simpler.
The second patch is the actual fix and has a detailed explanation in the
commit message.
This potential issue has existed for almost 10 years and I am unaware of
anyone actually hitting the race. I did not cc stable, but would be happy
to squash the patches and send to stable if anyone thinks that is a good
idea.
[1] https://lore.kernel.org/linux-mm/CAG48ez23q0Jy9cuVnwAe7t_fdhMk2S7N5Hdi-GLcCeq5bsfLxw@xxxxxxxxxxxxxx/
This patch (of 2):
I could not think of a reliable way to recreate the issue for testing.
Rather, I 'simulated errors' to exercise all the error paths.
The routine prep_compound_huge_page is a simple wrapper to call either
prep_compound_gigantic_page or prep_compound_page. However, it is only
called from gather_bootmem_prealloc which only processes gigantic pages.
Eliminate the routine and call prep_compound_gigantic_page directly.
Link: https://lkml.kernel.org/r/20210622021423.154662-1-mike.kravetz@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20210622021423.154662-2-mike.kravetz@xxxxxxxxxx
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Youquan Song <youquan.song@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 29 ++++++++++-------------------
1 file changed, 10 insertions(+), 19 deletions(-)
--- a/mm/hugetlb.c~hugetlb-remove-prep_compound_huge_page-cleanup
+++ a/mm/hugetlb.c
@@ -1320,8 +1320,6 @@ static struct page *alloc_gigantic_page(
return alloc_contig_pages(nr_pages, gfp_mask, nid, nodemask);
}
-static void prep_new_huge_page(struct hstate *h, struct page *page, int nid);
-static void prep_compound_gigantic_page(struct page *page, unsigned int order);
#else /* !CONFIG_CONTIG_ALLOC */
static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
int nid, nodemask_t *nodemask)
@@ -2759,16 +2757,10 @@ found:
return 1;
}
-static void __init prep_compound_huge_page(struct page *page,
- unsigned int order)
-{
- if (unlikely(order > (MAX_ORDER - 1)))
- prep_compound_gigantic_page(page, order);
- else
- prep_compound_page(page, order);
-}
-
-/* Put bootmem huge pages into the standard lists after mem_map is up */
+/*
+ * Put bootmem huge pages into the standard lists after mem_map is up.
+ * Note: This only applies to gigantic (order > MAX_ORDER) pages.
+ */
static void __init gather_bootmem_prealloc(void)
{
struct huge_bootmem_page *m;
@@ -2777,20 +2769,19 @@ static void __init gather_bootmem_preall
struct page *page = virt_to_page(m);
struct hstate *h = m->hstate;
+ VM_BUG_ON(!hstate_is_gigantic(h));
WARN_ON(page_count(page) != 1);
- prep_compound_huge_page(page, huge_page_order(h));
+ prep_compound_gigantic_page(page, huge_page_order(h));
WARN_ON(PageReserved(page));
prep_new_huge_page(h, page, page_to_nid(page));
put_page(page); /* free it into the hugepage allocator */
/*
- * If we had gigantic hugepages allocated at boot time, we need
- * to restore the 'stolen' pages to totalram_pages in order to
- * fix confusing memory reports from free(1) and another
- * side-effects, like CommitLimit going negative.
+ * We need to restore the 'stolen' pages to totalram_pages
+ * in order to fix confusing memory reports from free(1) and
+ * other side-effects, like CommitLimit going negative.
*/
- if (hstate_is_gigantic(h))
- adjust_managed_page_count(page, pages_per_huge_page(h));
+ adjust_managed_page_count(page, pages_per_huge_page(h));
cond_resched();
}
}
_
Patches currently in -mm which might be from mike.kravetz@xxxxxxxxxx are
mm-hugetlb-alloc-the-vmemmap-pages-associated-with-each-hugetlb-page-fix.patch
hugetlb-remove-prep_compound_huge_page-cleanup.patch
hugetlb-address-ref-count-racing-in-prep_compound_gigantic_page.patch
