vma_prepare() is currently the central place where vmas are being locked
before vma_complete() applies changes to them. While this is convenient,
it also obscures vma locking and makes it harder to follow the locking
rules. Move vma locking out of vma_prepare() and take vma locks
explicitly at the locations where vmas are being modified. Move vma
locking and replace it with an assertion inside dup_anon_vma() to further
clarify the locking pattern inside vma_merge().
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxx>
Suggested-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
mm/mmap.c | 30 +++++++++++++++++++-----------
1 file changed, 19 insertions(+), 11 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 850a39dee075..16661427d3e8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -476,16 +476,6 @@ static inline void init_vma_prep(struct vma_prepare *vp,
*/
static inline void vma_prepare(struct vma_prepare *vp)
{
- vma_start_write(vp->vma);
- if (vp->adj_next)
- vma_start_write(vp->adj_next);
- if (vp->insert)
- vma_start_write(vp->insert);
- if (vp->remove)
- vma_start_write(vp->remove);
- if (vp->remove2)
- vma_start_write(vp->remove2);
-
if (vp->file) {
uprobe_munmap(vp->vma, vp->vma->vm_start, vp->vma->vm_end);
@@ -618,7 +608,7 @@ static inline int dup_anon_vma(struct vm_area_struct *dst,
* anon pages imported.
*/
if (src->anon_vma && !dst->anon_vma) {
- vma_start_write(dst);
+ vma_assert_write_locked(dst);
dst->anon_vma = src->anon_vma;
return anon_vma_clone(dst, src);
}
@@ -650,10 +640,12 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
bool remove_next = false;
struct vma_prepare vp;
+ vma_start_write(vma);
if (next && (vma != next) && (end == next->vm_end)) {
int ret;
remove_next = true;
+ vma_start_write(next);
ret = dup_anon_vma(vma, next);
if (ret)
return ret;
@@ -708,6 +700,8 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (vma_iter_prealloc(vmi))
return -ENOMEM;
+ vma_start_write(vma);
+
init_vma_prep(&vp, vma);
vma_prepare(&vp);
vma_adjust_trans_huge(vma, start, end, 0);
@@ -940,16 +934,21 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
if (!merge_prev && !merge_next)
return NULL; /* Not mergeable. */
+ if (merge_prev)
+ vma_start_write(prev);
+
res = vma = prev;
remove = remove2 = adjust = NULL;
/* Can we merge both the predecessor and the successor? */
if (merge_prev && merge_next &&
is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
+ vma_start_write(next);
remove = next; /* case 1 */
vma_end = next->vm_end;
err = dup_anon_vma(prev, next);
if (curr) { /* case 6 */
+ vma_start_write(curr);
remove = curr;
remove2 = next;
if (!next->anon_vma)
@@ -957,6 +956,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
}
} else if (merge_prev) { /* case 2 */
if (curr) {
+ vma_start_write(curr);
err = dup_anon_vma(prev, curr);
if (end == curr->vm_end) { /* case 7 */
remove = curr;
@@ -966,8 +966,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
}
}
} else { /* merge_next */
+ vma_start_write(next);
res = next;
if (prev && addr < prev->vm_end) { /* case 4 */
+ vma_start_write(prev);
vma_end = addr;
adjust = next;
adj_start = -(prev->vm_end - addr);
@@ -983,6 +985,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
vma_pgoff = next->vm_pgoff - pglen;
if (curr) { /* case 8 */
vma_pgoff = curr->vm_pgoff;
+ vma_start_write(curr);
remove = curr;
err = dup_anon_vma(next, curr);
}
@@ -2373,6 +2376,9 @@ int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (new->vm_ops && new->vm_ops->open)
new->vm_ops->open(new);
+ vma_start_write(vma);
+ vma_start_write(new);
+
init_vma_prep(&vp, vma);
vp.insert = new;
vma_prepare(&vp);
@@ -3078,6 +3084,8 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (vma_iter_prealloc(vmi))
goto unacct_fail;
+ vma_start_write(vma);
+
init_vma_prep(&vp, vma);
vma_prepare(&vp);
vma_adjust_trans_huge(vma, vma->vm_start, addr + len, 0);
--
2.41.0.585.gd2178a4bd4-goog
