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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>
This commit is contained in:
Gerald Schaefer 2016-03-17 15:00:04 +01:00 committed by Martin Schwidefsky
parent 91d3721176
commit fc897c95e9
1 changed files with 5 additions and 3 deletions
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8
arch/s390/mm/gup.c
View File

@ -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)++;