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mm: move vma locking out of vma_prepare and dup_anon_vma

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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().

Link: https://lkml.kernel.org/r/20230804152724.3090321-7-surenb@google.com
Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org>
Suggested-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Suren Baghdasaryan 2023-08-04 08:27:24 -07:00 committed by Andrew Morton
parent ad9f006351
commit c9d6e982c3
1 changed files with 19 additions and 11 deletions
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30
mm/mmap.c
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@ -462,16 +462,6 @@ 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);
@ -605,7 +595,7 @@ 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);
}
@ -637,10 +627,12 @@ 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;
@ -696,6 +688,8 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (vma_iter_prealloc(vmi, NULL))
return -ENOMEM;
vma_start_write(vma);
init_vma_prep(&vp, vma);
vma_prepare(&vp);
vma_adjust_trans_huge(vma, start, end, 0);
@ -921,16 +915,21 @@ 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)
@ -938,6 +937,7 @@ 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;
@ -947,8 +947,10 @@ 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);
@ -964,6 +966,7 @@ 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);
}
@ -2366,6 +2369,9 @@ 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);
@ -3071,6 +3077,8 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
if (vma_iter_prealloc(vmi, vma))
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);