The patch titled
nommu: struct vm_region's vm_usage count need not be atomic
has been added to the -mm tree. Its filename is
nommu-struct-vm_regions-vm_usage-count-need-not-be-atomic.patch
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------------------------------------------------------
Subject: nommu: struct vm_region's vm_usage count need not be atomic
From: David Howells <dhowells@xxxxxxxxxx>
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: David Howells <dhowells@xxxxxxxxxx>
Acked-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Greg Ungerer <gerg@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm_types.h | 2 +-
mm/nommu.c | 14 +++++++-------
2 files changed, 8 insertions(+), 8 deletions(-)
diff -puN include/linux/mm_types.h~nommu-struct-vm_regions-vm_usage-count-need-not-be-atomic include/linux/mm_types.h
--- a/include/linux/mm_types.h~nommu-struct-vm_regions-vm_usage-count-need-not-be-atomic
+++ a/include/linux/mm_types.h
@@ -122,7 +122,7 @@ struct vm_region {
unsigned long vm_pgoff; /* the offset in vm_file corresponding to vm_start */
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
* this region */
};
diff -puN mm/nommu.c~nommu-struct-vm_regions-vm_usage-count-need-not-be-atomic mm/nommu.c
--- a/mm/nommu.c~nommu-struct-vm_regions-vm_usage-count-need-not-be-atomic
+++ a/mm/nommu.c
@@ -552,11 +552,11 @@ static void free_page_series(unsigned lo
static void __put_nommu_region(struct vm_region *region)
__releases(nommu_region_sem)
{
- kenter("%p{%d}", region, atomic_read(®ion->vm_usage));
+ kenter("%p{%d}", region, region->vm_usage);
BUG_ON(!nommu_region_tree.rb_node);
- if (atomic_dec_and_test(®ion->vm_usage)) {
+ if (--region->vm_usage == 0) {
if (region->vm_top > region->vm_start)
delete_nommu_region(region);
up_write(&nommu_region_sem);
@@ -1205,7 +1205,7 @@ unsigned long do_mmap_pgoff(struct file
if (!vma)
goto error_getting_vma;
- atomic_set(®ion->vm_usage, 1);
+ region->vm_usage = 1;
region->vm_flags = vm_flags;
region->vm_pgoff = pgoff;
@@ -1272,7 +1272,7 @@ unsigned long do_mmap_pgoff(struct file
}
/* we've found a region we can share */
- atomic_inc(&pregion->vm_usage);
+ pregion->vm_usage++;
vma->vm_region = pregion;
start = pregion->vm_start;
start += (pgoff - pregion->vm_pgoff) << PAGE_SHIFT;
@@ -1289,7 +1289,7 @@ unsigned long do_mmap_pgoff(struct file
vma->vm_region = NULL;
vma->vm_start = 0;
vma->vm_end = 0;
- atomic_dec(&pregion->vm_usage);
+ pregion->vm_usage--;
pregion = NULL;
goto error_just_free;
}
@@ -1444,7 +1444,7 @@ int split_vma(struct mm_struct *mm, stru
/* we're only permitted to split anonymous regions that have a single
* owner */
if (vma->vm_file ||
- atomic_read(&vma->vm_region->vm_usage) != 1)
+ vma->vm_region->vm_usage != 1)
return -ENOMEM;
if (mm->map_count >= sysctl_max_map_count)
@@ -1518,7 +1518,7 @@ static int shrink_vma(struct mm_struct *
/* cut the backing region down to size */
region = vma->vm_region;
- BUG_ON(atomic_read(®ion->vm_usage) != 1);
+ BUG_ON(region->vm_usage != 1);
down_write(&nommu_region_sem);
delete_nommu_region(region);
_
Patches currently in -mm which might be from dhowells@xxxxxxxxxx are
nommu-fix-sysv-shm-for-nommu.patch
nommu-struct-vm_regions-vm_usage-count-need-not-be-atomic.patch
nommu-remove-a-superfluous-check-of-vm_region-vm_usage.patch
nommu-dont-need-get_unmapped_area-for-nommu.patch
nommu-fix-race-between-ramfs-truncation-and-shared-mmap.patch
nommu-fix-shared-mmap-after-truncate-shrinkage-problems.patch
kernel-credc-use-kmem_cache_free.patch
nfs-avoid-warnings-when-config_nfs_v4=n.patch
frv-duplicate-output_buffer-of-e03.patch
coredump-unify-dump_seek-implementations-for-each-binfmt_c.patch
coredump-move-dump_write-and-dump_seek-into-a-header-file.patch
elf-coredump-replace-elf_core_extra_-macros-by-functions.patch
elf-coredump-make-offset-calculation-process-and-writing-process-explicit.patch
elf-coredump-add-extended-numbering-support.patch
mutex-subsystem-synchro-test-module.patch
mutex-subsystem-synchro-test-module-add-missing-header-file.patch
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