Commit 0e5ffe9b authored by Lorenzo Stoakes's avatar Lorenzo Stoakes Committed by Andrew Morton
Browse files

mm: make vmg->target consistent and further simplify commit_merge() 

It is confusing for vmg->target to sometimes be the target merged VMA and
in one case not.

Fix this by having commit_merge() use its awareness of the
vmg->_adjust_next_start case to know that it is manipulating a separate
vma, abstracted in the 'vma' local variable.

Place removal and adjust VMA determination logic into
init_multi_vma_prep(), as the flags give us enough information to do so,
and since this is the function that sets up the vma_prepare struct it
makes sense to do so here.

Doing this significantly simplifies commit_merge(), allowing us to
eliminate the 'merge_target' handling, initialise the VMA iterator in a
more sensible place and simply return vmg->target consistently.

This also allows us to simplify setting vmg->target in
vma_merge_existing_range() since we are then left only with two cases -
merge left (or both) where the target is vmg->prev or merge right in which
the target is vmg->next.

This makes it easy for somebody reading the code to know what VMA will
actually be the one returned and merged into and removes a great deal of
the confusing 'adjust' nonsense.

This patch has no change in functional behaviour.

Link: https://lkml.kernel.org/r/50f96e31ab1980eaaf1006e34a4f6e6dad9320b8.1738326519.git.lorenzo.stoakes@oracle.com


Signed-off-by: default avatarLorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent fe3e9cf0

mm/vma.c

+61 −58
Original line number Diff line number Diff line
@@ -106,24 +106,40 @@ static inline bool are_anon_vmas_compatible(struct vm_area_struct *vma1, 
 * init_multi_vma_prep() - Initializer for struct vma_prepare

 * @vp: The vma_prepare struct

 * @vma: The vma that will be altered once locked

 * @next: The next vma if it is to be adjusted

 * @remove: The first vma to be removed

 * @remove2: The second vma to be removed

 * @vmg: The merge state that will be used to determine adjustment and VMA

 *       removal.

 */

static void init_multi_vma_prep(struct vma_prepare *vp,

				struct vm_area_struct *vma,

				struct vm_area_struct *next,

				struct vm_area_struct *remove,

				struct vm_area_struct *remove2)

				struct vma_merge_struct *vmg)

{

	struct vm_area_struct *adjust;

	struct vm_area_struct **remove = &vp->remove;



	memset(vp, 0, sizeof(struct vma_prepare));

	vp->vma = vma;

	vp->anon_vma = vma->anon_vma;

	vp->remove = remove ? remove : remove2;

	vp->remove2 = remove ? remove2 : NULL;

	vp->adj_next = next;

	if (!vp->anon_vma && next)

		vp->anon_vma = next->anon_vma;



	if (vmg && vmg->__remove_middle) {

		*remove = vmg->middle;

		remove = &vp->remove2;

	}

	if (vmg && vmg->__remove_next)

		*remove = vmg->next;



	if (vmg && vmg->__adjust_middle_start)

		adjust = vmg->middle;

	else if (vmg && vmg->__adjust_next_start)

		adjust = vmg->next;

	else

		adjust = NULL;



	vp->adj_next = adjust;

	if (!vp->anon_vma && adjust)

		vp->anon_vma = adjust->anon_vma;



	VM_WARN_ON(vp->anon_vma && adjust && adjust->anon_vma &&

		   vp->anon_vma != adjust->anon_vma);



	vp->file = vma->vm_file;

	if (vp->file)
@@ -360,7 +376,7 @@ static void vma_complete(struct vma_prepare *vp, struct vma_iterator *vmi, 
 */

static void init_vma_prep(struct vma_prepare *vp, struct vm_area_struct *vma)

{

	init_multi_vma_prep(vp, vma, NULL, NULL, NULL);

	init_multi_vma_prep(vp, vma, NULL);

}



/*
@@ -634,76 +650,63 @@ void validate_mm(struct mm_struct *mm) 
 */

static struct vm_area_struct *commit_merge(struct vma_merge_struct *vmg)

{

	struct vm_area_struct *remove = NULL;

	struct vm_area_struct *remove2 = NULL;

	struct vm_area_struct *vma;

	struct vma_prepare vp;

	struct vm_area_struct *adjust = NULL;

	struct vm_area_struct *adjust;

	long adj_start;

	bool merge_target;



	/*

	 * If modifying an existing VMA and we don't remove vmg->middle, then we

	 * shrink the adjacent VMA.

	 */

	if (vmg->__adjust_middle_start) {

		vma = vmg->target;

		adjust = vmg->middle;

		/* The POSITIVE value by which we offset vmg->middle->vm_start. */

		adj_start = vmg->end - vmg->middle->vm_start;

		merge_target = true;



		 /* Note: vma iterator must be pointing to 'start'. */

		vma_iter_config(vmg->vmi, vmg->start, vmg->end);

	} else if (vmg->__adjust_next_start) {

		/*

		 * In this case alone, the VMA we manipulate is vmg->middle, but

		 * we ultimately return vmg->next.

		 */

		vma = vmg->middle;

		adjust = vmg->next;

		/* The NEGATIVE value by which we offset vmg->next->vm_start. */

		adj_start = -(vmg->middle->vm_end - vmg->end);

		/*

		 * In all cases but this - merge right, shrink next - we write

		 * vmg->target to the maple tree and return this as the merged VMA.

		 */

		merge_target = false;



		vma_iter_config(vmg->vmi, vmg->next->vm_start + adj_start,

				vmg->next->vm_end);

	} else {

		vma = vmg->target;

		adjust = NULL;

		adj_start = 0;

		merge_target = true;

	}



	if (vmg->__remove_middle)

		remove = vmg->middle;

	if (vmg->__remove_next)

		remove2 = vmg->next;



	init_multi_vma_prep(&vp, vmg->target, adjust, remove, remove2);



	VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&

		   vp.anon_vma != adjust->anon_vma);



	if (merge_target) {

		 /* Note: vma iterator must be pointing to 'start'. */

		vma_iter_config(vmg->vmi, vmg->start, vmg->end);

	} else {

		vma_iter_config(vmg->vmi, adjust->vm_start + adj_start,

				adjust->vm_end);

	}



	if (vma_iter_prealloc(vmg->vmi, vmg->target))

	init_multi_vma_prep(&vp, vma, vmg);



	if (vma_iter_prealloc(vmg->vmi, vma))

		return NULL;



	vma_prepare(&vp);

	vma_adjust_trans_huge(vmg->target, vmg->start, vmg->end, adj_start);

	vma_set_range(vmg->target, vmg->start, vmg->end, vmg->pgoff);



	if (merge_target)

		vma_iter_store(vmg->vmi, vmg->target);

	vma_adjust_trans_huge(vma, vmg->start, vmg->end, adj_start);

	vma_set_range(vma, vmg->start, vmg->end, vmg->pgoff);



	if (adj_start) {

		adjust->vm_start += adj_start;

		adjust->vm_pgoff += PHYS_PFN(adj_start);



		if (!merge_target)

			vma_iter_store(vmg->vmi, adjust);

	}



	vma_complete(&vp, vmg->vmi, vmg->target->vm_mm);

	vma_iter_store(vmg->vmi, vmg->target);



	vma_complete(&vp, vmg->vmi, vma->vm_mm);



	return merge_target ? vmg->target : vmg->next;

	return vmg->target;

}



/* We can only remove VMAs when merging if they do not have a close hook. */
@@ -833,11 +836,15 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( 
	/* No matter what happens, we will be adjusting middle. */

	vma_start_write(middle);



	if (merge_left)

		vma_start_write(prev);



	if (merge_right)

	if (merge_right) {

		vma_start_write(next);

		vmg->target = next;

	}



	if (merge_left) {

		vma_start_write(prev);

		vmg->target = prev;

	}



	if (merge_both) {

		/*
@@ -847,7 +854,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( 
		 *  extend  delete  delete

		 */



		vmg->target = prev;

		vmg->start = prev->vm_start;

		vmg->end = next->vm_end;

		vmg->pgoff = prev->vm_pgoff;
@@ -868,7 +874,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( 
		 *  extend shrink/delete

		 */



		vmg->target = prev;

		vmg->start = prev->vm_start;

		vmg->pgoff = prev->vm_pgoff;
@@ -892,7 +897,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( 
		VM_WARN_ON_VMG(vmg->start > middle->vm_start && prev && middle != prev, vmg);



		if (vmg->__remove_middle) {

			vmg->target = next;

			vmg->end = next->vm_end;

			vmg->pgoff = next->vm_pgoff - pglen;

		} else {
@@ -903,7 +907,6 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( 
			 * merged VMA is NOT vmg->target, but rather vmg->next.

			 */

			vmg->__adjust_next_start = true;

			vmg->target = middle;

			vmg->start = middle->vm_start;

			vmg->end = start;

			vmg->pgoff = middle->vm_pgoff;

mm/vma.h

+1 −5
Original line number Diff line number Diff line
@@ -82,11 +82,7 @@ struct vma_merge_struct { 
	struct vm_area_struct *prev;

	struct vm_area_struct *middle;

	struct vm_area_struct *next;

	/*

	 * This is the VMA we ultimately target to become the merged VMA, except

	 * for the one exception of merge right, shrink next (for details of

	 * this scenario see vma_merge_existing_range()).

	 */

	/* This is the VMA we ultimately target to become the merged VMA. */

	struct vm_area_struct *target;

	/*

	 * Initially, the start, end, pgoff fields are provided by the caller