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) <pet...@infradead.org>
---
include/linux/mm_types.h | 2 ++
mm/memory.c | 2 ++
mm/mmap.c | 13 +++++++++++++
3 files changed, 17 insertions(+)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -13,6 +13,7 @@
#include <linux/page-debug-flags.h>
#include <linux/uprobes.h>
#include <linux/page-flags-layout.h>
+#include <linux/seqlock.h>
#include <asm/page.h>
#include <asm/mmu.h>
@@ -308,6 +309,7 @@ struct vm_area_struct {
#ifdef CONFIG_NUMA
struct mempolicy *vm_policy; /* NUMA policy for the VMA */
#endif
+ seqcount_t vm_sequence;
};
struct core_thread {
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1293,6 +1293,7 @@ static void unmap_page_range(struct mmu_
details = NULL;
BUG_ON(addr >= end);
+ write_seqcount_begin(&vma->vm_sequence);
tlb_start_vma(tlb, vma);
pgd = pgd_offset(vma->vm_mm, addr);
do {
@@ -1302,6 +1303,7 @@ static void unmap_page_range(struct mmu_
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);
}
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -596,6 +596,8 @@ void __vma_link_rb(struct mm_struct *mm,
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
@@ -715,6 +717,10 @@ int vma_adjust(struct vm_area_struct *vm
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;
@@ -880,7 +886,10 @@ again: remove_next = 1 + (end > next->
* 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)
goto again;
else if (next)
@@ -891,6 +900,10 @@ again: remove_next = 1 + (end > next->
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;
--
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