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Commit 1e2ae599 authored by David Howells's avatar David Howells Committed by Linus Torvalds
Browse files

nommu: struct vm_region's vm_usage count need not be atomic 



The vm_usage count field in struct vm_region does not need to be atomic as
it's only even modified whilst nommu_region_sem is write locked.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Cc: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ed5e5894

include/linux/mm_types.h

+1 −1
Original line number Original line Diff line number Diff line
@@ -122,7 +122,7 @@ struct vm_region { 
	unsigned long	vm_pgoff;	/* the offset in vm_file corresponding to vm_start */

	unsigned long	vm_pgoff;	/* the offset in vm_file corresponding to vm_start */

	struct file	*vm_file;	/* the backing file or NULL */

	struct file	*vm_file;	/* the backing file or NULL */





	atomic_t	vm_usage;	/* region usage count */

	int		vm_usage;	/* region usage count (access under nommu_region_sem) */

	bool		vm_icache_flushed : 1; /* true if the icache has been flushed for

	bool		vm_icache_flushed : 1; /* true if the icache has been flushed for

						* this region */

						* this region */

};

};

mm/nommu.c

+7 −7
Original line number Original line Diff line number Diff line
@@ -552,11 +552,11 @@ static void free_page_series(unsigned long from, unsigned long to) 
static void __put_nommu_region(struct vm_region *region)

static void __put_nommu_region(struct vm_region *region)

	__releases(nommu_region_sem)

	__releases(nommu_region_sem)

{

{

	kenter("%p{%d}", region, atomic_read(&region->vm_usage));

	kenter("%p{%d}", region, region->vm_usage);





	BUG_ON(!nommu_region_tree.rb_node);

	BUG_ON(!nommu_region_tree.rb_node);





	if (atomic_dec_and_test(&region->vm_usage)) {

	if (--region->vm_usage == 0) {

		if (region->vm_top > region->vm_start)

		if (region->vm_top > region->vm_start)

			delete_nommu_region(region);

			delete_nommu_region(region);

		up_write(&nommu_region_sem);

		up_write(&nommu_region_sem);
@@ -1205,7 +1205,7 @@ unsigned long do_mmap_pgoff(struct file *file, 
	if (!vma)

	if (!vma)

		goto error_getting_vma;

		goto error_getting_vma;





	atomic_set(&region->vm_usage, 1);

	region->vm_usage = 1;

	region->vm_flags = vm_flags;

	region->vm_flags = vm_flags;

	region->vm_pgoff = pgoff;

	region->vm_pgoff = pgoff;
@@ -1272,7 +1272,7 @@ unsigned long do_mmap_pgoff(struct file *file, 
			}

			}





			/* we've found a region we can share */

			/* we've found a region we can share */

			atomic_inc(&pregion->vm_usage);

			pregion->vm_usage++;

			vma->vm_region = pregion;

			vma->vm_region = pregion;

			start = pregion->vm_start;

			start = pregion->vm_start;

			start += (pgoff - pregion->vm_pgoff) << PAGE_SHIFT;

			start += (pgoff - pregion->vm_pgoff) << PAGE_SHIFT;
@@ -1289,7 +1289,7 @@ unsigned long do_mmap_pgoff(struct file *file, 
					vma->vm_region = NULL;

					vma->vm_region = NULL;

					vma->vm_start = 0;

					vma->vm_start = 0;

					vma->vm_end = 0;

					vma->vm_end = 0;

					atomic_dec(&pregion->vm_usage);

					pregion->vm_usage--;

					pregion = NULL;

					pregion = NULL;

					goto error_just_free;

					goto error_just_free;

				}

				}
@@ -1444,7 +1444,7 @@ int split_vma(struct mm_struct *mm, struct vm_area_struct *vma, 
	/* we're only permitted to split anonymous regions that have a single

	/* we're only permitted to split anonymous regions that have a single

	 * owner */

	 * owner */

	if (vma->vm_file ||

	if (vma->vm_file ||

	    atomic_read(&vma->vm_region->vm_usage) != 1)

	    vma->vm_region->vm_usage != 1)

		return -ENOMEM;

		return -ENOMEM;





	if (mm->map_count >= sysctl_max_map_count)

	if (mm->map_count >= sysctl_max_map_count)
@@ -1518,7 +1518,7 @@ static int shrink_vma(struct mm_struct *mm, 




	/* cut the backing region down to size */

	/* cut the backing region down to size */

	region = vma->vm_region;

	region = vma->vm_region;

	BUG_ON(atomic_read(&region->vm_usage) != 1);

	BUG_ON(region->vm_usage != 1);





	down_write(&nommu_region_sem);

	down_write(&nommu_region_sem);

	delete_nommu_region(region);

	delete_nommu_region(region);