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Subject[PATCH v3 04/20] mm: VMA sequence count
Date
From: Peter Zijlstra <peterz@infradead.org>

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@infradead.org>

[Port to 4.12 kernel]
[Fix lock dependency between mapping->i_mmap_rwsem and vma->vm_sequence]
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
---
include/linux/mm_types.h | 1 +
mm/memory.c | 2 ++
mm/mmap.c | 21 ++++++++++++++++++---
3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 46f4ecf5479a..df9a530c8ca1 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -344,6 +344,7 @@ 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;
} __randomize_layout;

struct core_thread {
diff --git a/mm/memory.c b/mm/memory.c
index 530d887ca885..f250e7c92948 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1499,6 +1499,7 @@ 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 {
@@ -1508,6 +1509,7 @@ 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 680506faceae..0a0012c7e50c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -558,6 +558,8 @@ void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
else
mm->highest_vm_end = vm_end_gap(vma);

+ 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
@@ -799,6 +801,11 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
}
}

+ write_seqcount_begin(&vma->vm_sequence);
+ if (next && next != vma)
+ write_seqcount_begin_nested(&next->vm_sequence,
+ SINGLE_DEPTH_NESTING);
+
anon_vma = vma->anon_vma;
if (!anon_vma && adjust_next)
anon_vma = next->anon_vma;
@@ -903,6 +910,7 @@ 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
@@ -932,11 +940,14 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
if (remove_next == 2) {
remove_next = 1;
end = next->vm_end;
+ write_seqcount_end(&vma->vm_sequence);
goto again;
- }
- else if (next)
+ } else if (next) {
+ if (next != vma)
+ write_seqcount_begin_nested(&next->vm_sequence,
+ SINGLE_DEPTH_NESTING);
vma_gap_update(next);
- else {
+ } else {
/*
* If remove_next == 2 we obviously can't
* reach this path.
@@ -962,6 +973,10 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
if (insert && file)
uprobe_mmap(insert);

+ if (next && next != vma)
+ write_seqcount_end(&next->vm_sequence);
+ write_seqcount_end(&vma->vm_sequence);
+
validate_mm(mm);

return 0;
--
2.7.4
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