Commit 0173db4f authored by Lorenzo Stoakes's avatar Lorenzo Stoakes Committed by Andrew Morton
Browse files

mm/mmap/vma_merge: init cleanup, be explicit about the non-mergeable case 

Rather than setting err = -1 and only resetting if we hit merge cases,
explicitly check the non-mergeable case to make it abundantly clear that
we only proceed with the rest if something is mergeable, default err to 0
and only update if an error might occur.

Move the merge_prev, merge_next cases closer to the logic determining
curr, next and reorder initial variables so they are more logically
grouped.

This has no functional impact.

Link: https://lkml.kernel.org/r/99259fbc6403e80e270e1cc4612abbc8620b121b.1679516210.git.lstoakes@gmail.com


Signed-off-by: default avatarLorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent b0729ae0

mm/mmap.c

+22 −25
Original line number Diff line number Diff line
@@ -896,18 +896,18 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 
			struct vm_userfaultfd_ctx vm_userfaultfd_ctx,

			struct anon_vma_name *anon_name)

{

	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;

	pgoff_t vma_pgoff;

	struct vm_area_struct *curr, *next, *res;

	struct vm_area_struct *vma, *adjust, *remove, *remove2;

	int err = -1;

	struct vma_prepare vp;

	pgoff_t vma_pgoff;

	int err = 0;

	bool merge_prev = false;

	bool merge_next = false;

	bool vma_expanded = false;

	struct vma_prepare vp;

	unsigned long vma_start = addr;

	unsigned long vma_end = end;

	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;

	long adj_start = 0;

	unsigned long vma_start = addr;



	validate_mm(mm);

	/*
@@ -926,22 +926,12 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 
	else

		next = NULL;		/* case 5 */



	/*

	 * By default, we return prev. Cases 3, 4, 8 will instead return next

	 * and cases 3, 8 will also update vma to point at next.

	 */

	res = vma = prev;



	/* Verify some invariant that must be enforced by the caller. */

	VM_WARN_ON(prev && addr <= prev->vm_start);

	VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));

	VM_WARN_ON(addr >= end);



	if (prev) {

		vma_start = prev->vm_start;

		vma_pgoff = prev->vm_pgoff;



		/* Can we merge the predecessor? */

		if (prev->vm_end == addr && mpol_equal(vma_policy(prev), policy)

		if (addr == prev->vm_end && mpol_equal(vma_policy(prev), policy)

		    && can_vma_merge_after(prev, vm_flags, anon_vma, file,

					   pgoff, vm_userfaultfd_ctx, anon_name)) {

			merge_prev = true;
@@ -951,13 +941,22 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 


	/* Can we merge the successor? */

	if (next && mpol_equal(policy, vma_policy(next)) &&

	    can_vma_merge_before(next, vm_flags,

				 anon_vma, file, pgoff+pglen,

	    can_vma_merge_before(next, vm_flags, anon_vma, file, pgoff+pglen,

				 vm_userfaultfd_ctx, anon_name)) {

		merge_next = true;

	}



	if (!merge_prev && !merge_next)

		return NULL; /* Not mergeable. */



	res = vma = prev;

	remove = remove2 = adjust = NULL;



	/* Verify some invariant that must be enforced by the caller. */

	VM_WARN_ON(prev && addr <= prev->vm_start);

	VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));

	VM_WARN_ON(addr >= end);



	/* 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)) {
@@ -970,8 +969,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 
			if (!next->anon_vma)

				err = dup_anon_vma(prev, curr);

		}

	} else if (merge_prev) {

		err = 0;				/* case 2 */

	} else if (merge_prev) {			/* case 2 */

		if (curr) {

			err = dup_anon_vma(prev, curr);

			if (end == curr->vm_end) {	/* case 7 */
@@ -981,7 +979,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 
				adj_start = (end - curr->vm_start);

			}

		}

	} else if (merge_next) {

	} else { /* merge_next */

		res = next;

		if (prev && addr < prev->vm_end) {	/* case 4 */

			vma_end = addr;
@@ -997,7 +995,6 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 
			vma_start = addr;

			vma_end = next->vm_end;

			vma_pgoff = next->vm_pgoff;

			err = 0;

			if (curr) {			/* case 8 */

				vma_pgoff = curr->vm_pgoff;

				remove = curr;
@@ -1006,7 +1003,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, 
		}

	}



	/* Cannot merge or error in anon_vma clone */

	/* Error in anon_vma clone. */

	if (err)

		return NULL;