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Subject[RFC v5 PATCH 1/2] mm: refactor do_munmap() to extract the common part
Date
Introduces three new helper functions:
* munmap_addr_sanity()
* munmap_lookup_vma()
* munmap_mlock_vma()

They will be used by do_munmap() and the new do_munmap with zapping
large mapping early in the later patch.

There is no functional change, just code refactor.

Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
mm/mmap.c | 120 ++++++++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 82 insertions(+), 38 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index d1eb87e..2504094 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2686,34 +2686,44 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
return __split_vma(mm, vma, addr, new_below);
}

-/* Munmap is split into 2 main parts -- this part which finds
- * what needs doing, and the areas themselves, which do the
- * work. This now handles partial unmappings.
- * Jeremy Fitzhardinge <jeremy@goop.org>
- */
-int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
- struct list_head *uf)
+static inline bool munmap_addr_sanity(unsigned long start, size_t len)
{
- unsigned long end;
- struct vm_area_struct *vma, *prev, *last;
-
if ((offset_in_page(start)) || start > TASK_SIZE || len > TASK_SIZE-start)
- return -EINVAL;
+ return false;

- len = PAGE_ALIGN(len);
- if (len == 0)
- return -EINVAL;
+ if (PAGE_ALIGN(len) == 0)
+ return false;
+
+ return true;
+}
+
+/*
+ * munmap_lookup_vma: find the first overlap vma and split overlap vmas.
+ * @mm: mm_struct
+ * @vma: the first overlapping vma
+ * @prev: vma's prev
+ * @start: start address
+ * @end: end address
+ *
+ * returns 1 if successful, 0 or errno otherwise
+ */
+static int munmap_lookup_vma(struct mm_struct *mm, struct vm_area_struct **vma,
+ struct vm_area_struct **prev, unsigned long start,
+ unsigned long end)
+{
+ struct vm_area_struct *tmp, *last;

/* Find the first overlapping VMA */
- vma = find_vma(mm, start);
- if (!vma)
+ tmp = find_vma(mm, start);
+ if (!tmp)
return 0;
- prev = vma->vm_prev;
- /* we have start < vma->vm_end */
+
+ *prev = tmp->vm_prev;
+
+ /* we have start < vma->vm_end */

/* if it doesn't overlap, we have nothing.. */
- end = start + len;
- if (vma->vm_start >= end)
+ if (tmp->vm_start >= end)
return 0;

/*
@@ -2723,7 +2733,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
* unmapped vm_area_struct will remain in use: so lower split_vma
* places tmp vma above, and higher split_vma places tmp vma below.
*/
- if (start > vma->vm_start) {
+ if (start > tmp->vm_start) {
int error;

/*
@@ -2731,13 +2741,14 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
* not exceed its limit; but let map_count go just above
* its limit temporarily, to help free resources as expected.
*/
- if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
+ if (end < tmp->vm_end &&
+ mm->map_count > sysctl_max_map_count)
return -ENOMEM;

- error = __split_vma(mm, vma, start, 0);
+ error = __split_vma(mm, tmp, start, 0);
if (error)
return error;
- prev = vma;
+ *prev = tmp;
}

/* Does it split the last one? */
@@ -2747,7 +2758,48 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
if (error)
return error;
}
- vma = prev ? prev->vm_next : mm->mmap;
+
+ *vma = *prev ? (*prev)->vm_next : mm->mmap;
+
+ return 1;
+}
+
+static inline void munmap_mlock_vma(struct vm_area_struct *vma,
+ unsigned long end)
+{
+ struct vm_area_struct *tmp = vma;
+
+ while (tmp && tmp->vm_start < end) {
+ if (tmp->vm_flags & VM_LOCKED) {
+ vma->vm_mm->locked_vm -= vma_pages(tmp);
+ munlock_vma_pages_all(tmp);
+ }
+ tmp = tmp->vm_next;
+ }
+}
+
+/* Munmap is split into 2 main parts -- this part which finds
+ * what needs doing, and the areas themselves, which do the
+ * work. This now handles partial unmappings.
+ * Jeremy Fitzhardinge <jeremy@goop.org>
+ */
+int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
+ struct list_head *uf)
+{
+ unsigned long end;
+ struct vm_area_struct *vma = NULL, *prev;
+ int ret = 0;
+
+ if (!munmap_addr_sanity(start, len))
+ return -EINVAL;
+
+ len = PAGE_ALIGN(len);
+
+ end = start + len;
+
+ ret = munmap_lookup_vma(mm, &vma, &prev, start, end);
+ if (ret != 1)
+ return ret;

if (unlikely(uf)) {
/*
@@ -2759,24 +2811,16 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
* split, despite we could. This is unlikely enough
* failure that it's not worth optimizing it for.
*/
- int error = userfaultfd_unmap_prep(vma, start, end, uf);
- if (error)
- return error;
+ ret = userfaultfd_unmap_prep(vma, start, end, uf);
+ if (ret)
+ return ret;
}

/*
* unlock any mlock()ed ranges before detaching vmas
*/
- if (mm->locked_vm) {
- struct vm_area_struct *tmp = vma;
- while (tmp && tmp->vm_start < end) {
- if (tmp->vm_flags & VM_LOCKED) {
- mm->locked_vm -= vma_pages(tmp);
- munlock_vma_pages_all(tmp);
- }
- tmp = tmp->vm_next;
- }
- }
+ if (mm->locked_vm)
+ munmap_mlock_vma(vma, end);

/*
* Remove the vma's, and unmap the actual pages
--
1.8.3.1
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