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Subject[RFC v7 PATCH 1/4] mm: refactor do_munmap() to extract the common part
Date
Introduces three new helper functions:
* addr_ok()
* munmap_lookup_vma()
* munlock_vmas()

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.

Reviewed-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
---
mm/mmap.c | 100 ++++++++++++++++++++++++++++++++++++++++++++------------------
1 file changed, 71 insertions(+), 29 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 17bbf4d..2a6898b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2681,35 +2681,40 @@ 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 addr_ok(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
+ * @start: start address
+ * @end: end address
+ *
+ * returns the pointer to vma, NULL or err ptr when spilt_vma returns error.
+ */
+static struct vm_area_struct *munmap_lookup_vma(struct mm_struct *mm,
+ unsigned long start, unsigned long end)
+{
+ struct vm_area_struct *vma, *prev, *last;

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

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

/*
* If we need to split any vma, do it now to save pain later.
@@ -2727,11 +2732,11 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
* its limit temporarily, to help free resources as expected.
*/
if (end < vma->vm_end && mm->map_count >= sysctl_max_map_count)
- return -ENOMEM;
+ return ERR_PTR(-ENOMEM);

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

@@ -2740,10 +2745,53 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
if (last && end > last->vm_start) {
int error = __split_vma(mm, last, end, 1);
if (error)
- return error;
+ return ERR_PTR(error);
}
vma = prev ? prev->vm_next : mm->mmap;

+ return vma;
+}
+
+static inline void munlock_vmas(struct vm_area_struct *vma,
+ unsigned long end)
+{
+ struct mm_struct *mm = vma->vm_mm;
+
+ while (vma && vma->vm_start < end) {
+ if (vma->vm_flags & VM_LOCKED) {
+ mm->locked_vm -= vma_pages(vma);
+ munlock_vma_pages_all(vma);
+ }
+ vma = vma->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, *prev;
+
+ if (!addr_ok(start, len))
+ return -EINVAL;
+
+ len = PAGE_ALIGN(len);
+
+ end = start + len;
+
+ vma = munmap_lookup_vma(mm, start, end);
+ if (!vma)
+ return 0;
+ if (IS_ERR(vma))
+ return PTR_ERR(vma);
+
+ prev = vma->vm_prev;
+
if (unlikely(uf)) {
/*
* If userfaultfd_unmap_prep returns an error the vmas
@@ -2764,13 +2812,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
*/
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;
- }
+ munlock_vmas(tmp, end);
}

/*
--
1.8.3.1
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