From: Will Deacon <[email protected]> commit a3e328556d41bb61c55f9dfcc62d6a826ea97b85 upstream.
When operating on hugepages with DEBUG_VM enabled, the GUP code checks the compound head for each tail page prior to calling page_cache_add_speculative. This is broken, because on the fast-GUP path (where we don't hold any page table locks) we can be racing with a concurrent invocation of split_huge_page_to_list. split_huge_page_to_list deals with this race by using page_ref_freeze to freeze the page and force concurrent GUPs to fail whilst the component pages are modified. This modification includes clearing the compound_head field for the tail pages, so checking this prior to a successful call to page_cache_add_speculative can lead to false positives: In fact, page_cache_add_speculative *already* has this check once the page refcount has been successfully updated, so we can simply remove the broken calls to VM_BUG_ON_PAGE. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Will Deacon <[email protected]> Signed-off-by: Punit Agrawal <[email protected]> Acked-by: Steve Capper <[email protected]> Acked-by: Kirill A. Shutemov <[email protected]> Cc: Aneesh Kumar K.V <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: Naoya Horiguchi <[email protected]> Cc: Mark Rutland <[email protected]> Cc: Hillf Danton <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Mike Kravetz <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Srivatsa S. Bhat (VMware) <[email protected]> Signed-off-by: Ajay Kaher <[email protected]> --- mm/gup.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 45c544b..6e7cfaa 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1136,7 +1136,6 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); tail = page; do { - VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; @@ -1183,7 +1182,6 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); tail = page; do { - VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; @@ -1226,7 +1224,6 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT); tail = page; do { - VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; -- 2.7.4
