Commit fc897c95 authored Mar 17, 2016 by Gerald Schaefer Committed by Martin Schwidefsky Mar 17, 2016

s390/mm: handle PTE-mapped tail pages in fast gup



With the THP refcounting rework it is possible to see THP compound tail
pages mapped with PTEs during a THP split. This needs to be considered
when using page_cache_get_speculative(), which will always fail on tail
pages because ->_count is always zero. commit 7aef4172 "mm: handle
PTE-mapped tail pages in gerneric fast gup implementaiton" fixed it for
the generic fast gup code by using compound_head(page) instead of page,
but not for s390.

This patch is a 1:1 adaption of commit 7aef4172 for the s390 fast gup
code. Without this fix, gup will fall back to the slow path or fail
in the unlikely scenario that we hit a THP under splitting in-between
the page table split and the compound page split.

Cc: stable@vger.kernel.org # v4.5
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent 91d37211

arch/s390/mm/gup.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -20,9 +20,9 @@
		static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
		unsigned long end, int write, struct page *pages, int nr)
		{
		struct page head, page;
		unsigned long mask;
		pte_t *ptep, pte;
		struct page *page;

		mask = (write ? _PAGE_PROTECT : 0) \| _PAGE_INVALID \| _PAGE_SPECIAL;

		@@ -37,12 +37,14 @@ static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
		return 0;
		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
		page = pte_page(pte);
		if (!page_cache_get_speculative(page))
		head = compound_head(page);
		if (!page_cache_get_speculative(head))
		return 0;
		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
		put_page(page);
		put_page(head);
		return 0;
		}
		VM_BUG_ON_PAGE(compound_head(page) != head, page);
		pages[*nr] = page;
		(*nr)++;

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