Commit 5ff783f1 authored Mar 09, 2023 by Vlastimil Babka Committed by Andrew Morton Apr 05, 2023

mm/mmap/vma_merge: use the proper vma pointers in cases 1 and 6

Case 1 is now shown in the comment as next vma being merged with prev, so
use 'next' instead of 'mid'.  In case 1 they both point to the same vma.

As a consequence, in case 6, the dup_anon_vma() is now tried first on
'next' and then on 'mid', before it was the opposite order.  This is not a
functional change, as those two vma's cannnot have a different anon_vma,
as that would have prevented the merging in the first place.

Link: https://lkml.kernel.org/r/20230309111258.24079-4-vbabka@suse.cz


Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 097d70c6

mm/mmap.c

+6 −5

Original line number	Diff line number	Diff line
		@@ -605,7 +605,7 @@ static inline void vma_complete(struct vma_prepare *vp,

		/*
		* In mprotect's case 6 (see comments on vma_merge),
		* we must remove the one after next as well.
		* we are removing both mid and next vmas
		*/
		if (vp->remove2) {
		vp->remove = vp->remove2;
		@@ -948,13 +948,14 @@ struct vm_area_struct vma_merge(struct vma_iterator vmi, struct mm_struct *mm,
		/* 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)) {
		remove = mid; /* case 1 */
		remove = next; /* case 1 */
		vma_end = next->vm_end;
		err = dup_anon_vma(prev, mid);
		err = dup_anon_vma(prev, next);
		if (mid != next) { /* case 6 */
		remove = mid;
		remove2 = next;
		if (!mid->anon_vma)
		err = dup_anon_vma(prev, next);
		if (!next->anon_vma)
		err = dup_anon_vma(prev, mid);
		}
		} else if (merge_prev) {
		err = 0; /* case 2 */