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>
---
include/linux/mm_types.h | 1 +
mm/memory.c | 2 ++
mm/mmap.c | 12 ++++++++++++
3 files changed, 15 insertions(+)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 903200f4ec41..620719bef808 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -358,6 +358,7 @@ 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 d19800904272..ec32cf710403 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1290,6 +1290,7 @@ 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 {
@@ -1299,6 +1300,7 @@ void unmap_page_range(struct mmu_gather *tlb,
next = zap_pud_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 ca9d91bca0d6..c2be9bd0ad92 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -514,6 +514,8 @@ 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
@@ -629,6 +631,10 @@ 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;
@@ -802,7 +808,9 @@ again:
* we must remove another next too. It would clutter
* up the code too much to do both in one go.
*/
+ write_seqcount_end(&next->vm_sequence);
next = vma->vm_next;
+ write_seqcount_begin_nested(&next->vm_sequence, SINGLE_DEPTH_NESTING);
if (remove_next == 2) {
remove_next = 1;
end = next->vm_end;
@@ -816,6 +824,10 @@ again:
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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