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authorAndrea Arcangeli <aarcange@redhat.com>2017-02-23 02:44:12 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2017-02-23 03:41:29 +0300
commit175ad4f1e7a29c8f914254e2e6316c50671e027a (patch)
treeecc4847e73314b2cc2db78f6a24e2f9e78b47905 /mm/mprotect.c
parent7a0c4cf85b856430af62a907dd65dfc51438d24f (diff)
downloadlinux-175ad4f1e7a29c8f914254e2e6316c50671e027a.tar.xz
mm: mprotect: use pmd_trans_unstable instead of taking the pmd_lock
pmd_trans_unstable does an atomic read on the pmd so it doesn't require the pmd_lock for the same check. This also removes the special assumption that the mmap_sem is hold for writing if prot_numa is not set. userfaultfd will hold the mmap_sem only for reading in change_pte_range like prot_numa, but it will not set prot_numa. This is always a valid micro-optimization regardless of userfaultfd. [kirill@shutemov.name: drop unneeded pmd_trans_unstable(pmd) check after __split_huge_pmd()] Link: http://lkml.kernel.org/r/20170208120421.GE5578@node.shutemov.name Link: http://lkml.kernel.org/r/20161216144821.5183-43-aarcange@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com> Cc: Hillf Danton <hillf.zj@alibaba-inc.com> Cc: Michael Rapoport <RAPOPORT@il.ibm.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/mprotect.c')
-rw-r--r--mm/mprotect.c46
1 files changed, 15 insertions, 31 deletions
diff --git a/mm/mprotect.c b/mm/mprotect.c
index f9c07f54dd62..a45b4dc6a7f5 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -33,34 +33,6 @@
#include "internal.h"
-/*
- * For a prot_numa update we only hold mmap_sem for read so there is a
- * potential race with faulting where a pmd was temporarily none. This
- * function checks for a transhuge pmd under the appropriate lock. It
- * returns a pte if it was successfully locked or NULL if it raced with
- * a transhuge insertion.
- */
-static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
- unsigned long addr, int prot_numa, spinlock_t **ptl)
-{
- pte_t *pte;
- spinlock_t *pmdl;
-
- /* !prot_numa is protected by mmap_sem held for write */
- if (!prot_numa)
- return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
-
- pmdl = pmd_lock(vma->vm_mm, pmd);
- if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
- spin_unlock(pmdl);
- return NULL;
- }
-
- pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
- spin_unlock(pmdl);
- return pte;
-}
-
static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot,
int dirty_accountable, int prot_numa)
@@ -71,7 +43,21 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long pages = 0;
int target_node = NUMA_NO_NODE;
- pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
+ /*
+ * Can be called with only the mmap_sem for reading by
+ * prot_numa so we must check the pmd isn't constantly
+ * changing from under us from pmd_none to pmd_trans_huge
+ * and/or the other way around.
+ */
+ if (pmd_trans_unstable(pmd))
+ return 0;
+
+ /*
+ * The pmd points to a regular pte so the pmd can't change
+ * from under us even if the mmap_sem is only hold for
+ * reading.
+ */
+ pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
if (!pte)
return 0;
@@ -177,8 +163,6 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
if (next - addr != HPAGE_PMD_SIZE) {
__split_huge_pmd(vma, pmd, addr, false, NULL);
- if (pmd_trans_unstable(pmd))
- continue;
} else {
int nr_ptes = change_huge_pmd(vma, pmd, addr,
newprot, prot_numa);