From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Wrap the VMA modifications (vma_adjust/unmap_page_range) with sequence
counts such that we can easily test if a VMA is changed.
The unmap_page_range() one allows us to make assumptions about
page-tables; when we find the seqcount hasn't changed we can assume
page-tables are still valid.
The flip side is that we cannot distinguish between a vma_adjust() and
the unmap_page_range() -- where with the former we could have
re-checked the vma bounds against the address.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
[port to 4.12 kernel]
Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
---
include/linux/mm_types.h | 1 +
mm/memory.c | 2 ++
mm/mmap.c | 13 +++++++++++++
3 files changed, 16 insertions(+)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 45cdb27791a3..8945743e4609 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -342,6 +342,7 @@ struct vm_area_struct {
struct mempolicy *vm_policy; /* NUMA policy for the VMA */
#endif
struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
+ seqcount_t vm_sequence;
};
struct core_thread {
diff --git a/mm/memory.c b/mm/memory.c
index f1132f7931ef..5d259cd67a83 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1379,6 +1379,7 @@ void unmap_page_range(struct mmu_gather *tlb,
unsigned long next;
BUG_ON(addr >= end);
+ write_seqcount_begin(&vma->vm_sequence);
tlb_start_vma(tlb, vma);
pgd = pgd_offset(vma->vm_mm, addr);
do {
@@ -1388,6 +1389,7 @@ void unmap_page_range(struct mmu_gather *tlb,
next = zap_p4d_range(tlb, vma, pgd, addr, next, details);
} while (pgd++, addr = next, addr != end);
tlb_end_vma(tlb, vma);
+ write_seqcount_end(&vma->vm_sequence);
}
diff --git a/mm/mmap.c b/mm/mmap.c
index f82741e199c0..9f86356d0012 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -543,6 +543,8 @@ void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
else
mm->highest_vm_end = vma->vm_end;
+ seqcount_init(&vma->vm_sequence);
+
/*
* vma->vm_prev wasn't known when we followed the rbtree to find the
* correct insertion point for that vma. As a result, we could not
@@ -677,6 +679,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
long adjust_next = 0;
int remove_next = 0;
+ write_seqcount_begin(&vma->vm_sequence);
+ if (next)
+ write_seqcount_begin_nested(&next->vm_sequence, SINGLE_DEPTH_NESTING);
+
if (next && !insert) {
struct vm_area_struct *exporter = NULL, *importer = NULL;
@@ -888,6 +894,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
mm->map_count--;
mpol_put(vma_policy(next));
kmem_cache_free(vm_area_cachep, next);
+ write_seqcount_end(&next->vm_sequence);
/*
* In mprotect's case 6 (see comments on vma_merge),
* we must remove another next too. It would clutter
@@ -901,6 +908,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
* "vma->vm_next" gap must be updated.
*/
next = vma->vm_next;
+ if (next)
+ write_seqcount_begin_nested(&next->vm_sequence, SINGLE_DEPTH_NESTING);
} else {
/*
* For the scope of the comment "next" and
@@ -947,6 +956,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
if (insert && file)
uprobe_mmap(insert);
+ if (next)
+ write_seqcount_end(&next->vm_sequence);
+ write_seqcount_end(&vma->vm_sequence);
+
validate_mm(mm);
return 0;
--
2.7.4
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