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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-20 16:48:59 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-20 16:48:59 -0800 |
| commit | 60815cf2e05057db5b78e398d9734c493560b11e (patch) | |
| tree | 23d7f55df13cc5a0c072cc8a6f361f8e7050b825 /mm | |
| parent | bfc7249cc293deac8f2678b7ec3d2407b68c0a33 (diff) | |
| parent | 5de72a2247ac05bde7c89039631b3d0c6186fafb (diff) | |
Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux
Pull ACCESS_ONCE cleanup preparation from Christian Borntraeger:
"kernel: Provide READ_ONCE and ASSIGN_ONCE
As discussed on LKML http://marc.info/?i=54611D86.4040306%40de.ibm.com
ACCESS_ONCE might fail with specific compilers for non-scalar
accesses.
Here is a set of patches to tackle that problem.
The first patch introduce READ_ONCE and ASSIGN_ONCE. If the data
structure is larger than the machine word size memcpy is used and a
warning is emitted. The next patches fix up several in-tree users of
ACCESS_ONCE on non-scalar types.
This does not yet contain a patch that forces ACCESS_ONCE to work only
on scalar types. This is targetted for the next merge window as Linux
next already contains new offenders regarding ACCESS_ONCE vs.
non-scalar types"
* tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux:
s390/kvm: REPLACE barrier fixup with READ_ONCE
arm/spinlock: Replace ACCESS_ONCE with READ_ONCE
arm64/spinlock: Replace ACCESS_ONCE READ_ONCE
mips/gup: Replace ACCESS_ONCE with READ_ONCE
x86/gup: Replace ACCESS_ONCE with READ_ONCE
x86/spinlock: Replace ACCESS_ONCE with READ_ONCE
mm: replace ACCESS_ONCE with READ_ONCE or barriers
kernel: Provide READ_ONCE and ASSIGN_ONCE
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/gup.c | 2 | ||||
| -rw-r--r-- | mm/memory.c | 11 | ||||
| -rw-r--r-- | mm/rmap.c | 3 |
3 files changed, 13 insertions, 3 deletions
@@ -968,7 +968,7 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, pudp = pud_offset(&pgd, addr); do { - pud_t pud = ACCESS_ONCE(*pudp); + pud_t pud = READ_ONCE(*pudp); next = pud_addr_end(addr, end); if (pud_none(pud)) diff --git a/mm/memory.c b/mm/memory.c index d8aebc52265f..649e7d440bd7 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3195,7 +3195,16 @@ static int handle_pte_fault(struct mm_struct *mm, pte_t entry; spinlock_t *ptl; - entry = ACCESS_ONCE(*pte); + /* + * some architectures can have larger ptes than wordsize, + * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and CONFIG_32BIT=y, + * so READ_ONCE or ACCESS_ONCE cannot guarantee atomic accesses. + * The code below just needs a consistent view for the ifs and + * we later double check anyway with the ptl lock held. So here + * a barrier will do. + */ + entry = *pte; + barrier(); if (!pte_present(entry)) { if (pte_none(entry)) { if (vma->vm_ops) { diff --git a/mm/rmap.c b/mm/rmap.c index 45ba250babd8..c5bc241127b2 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -583,7 +583,8 @@ pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address) * without holding anon_vma lock for write. So when looking for a * genuine pmde (in which to find pte), test present and !THP together. */ - pmde = ACCESS_ONCE(*pmd); + pmde = *pmd; + barrier(); if (!pmd_present(pmde) || pmd_trans_huge(pmde)) pmd = NULL; out: |