mm: use helper functions for allocating and freeing vm_area structs

The vm_area_struct is one of the most fundamental memory management
objects, but the management of it is entirely open-coded evertwhere,
ranging from allocation and freeing (using kmem_cache_[z]alloc and
kmem_cache_free) to initializing all the fields.

We want to unify this in order to end up having some unified
initialization of the vmas, and the first step to this is to at least
have basic allocation functions.

Right now those functions are literally just wrappers around the
kmem_cache_*() calls.  This is a purely mechanical conversion:

    # new vma:
    kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL) -> vm_area_alloc()

    # copy old vma
    kmem_cache_alloc(vm_area_cachep, GFP_KERNEL) -> vm_area_dup(old)

    # free vma
    kmem_cache_free(vm_area_cachep, vma) -> vm_area_free(vma)

to the point where the old vma passed in to the vm_area_dup() function
isn't even used yet (because I've left all the old manual initialization
alone).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 3 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 9440d61b925c..0e23deb5acfc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -303,11 +303,26 @@ struct kmem_cache *files_cachep;
 struct kmem_cache *fs_cachep;
 
 /* SLAB cache for vm_area_struct structures */
-struct kmem_cache *vm_area_cachep;
+static struct kmem_cache *vm_area_cachep;
 
 /* SLAB cache for mm_struct structures (tsk->mm) */
 static struct kmem_cache *mm_cachep;
 
+struct vm_area_struct *vm_area_alloc(void)
+{
+	return kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
+}
+
+struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
+{
+	return kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+}
+
+void vm_area_free(struct vm_area_struct *vma)
+{
+	kmem_cache_free(vm_area_cachep, vma);
+}
+
 static void account_kernel_stack(struct task_struct *tsk, int account)
 {
 	void *stack = task_stack_page(tsk);
@@ -455,7 +470,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
 				goto fail_nomem;
 			charge = len;
 		}
-		tmp = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
+		tmp = vm_area_dup(mpnt);
 		if (!tmp)
 			goto fail_nomem;
 		*tmp = *mpnt;
@@ -539,7 +554,7 @@ fail_uprobe_end:
 fail_nomem_anon_vma_fork:
 	mpol_put(vma_policy(tmp));
 fail_nomem_policy:
-	kmem_cache_free(vm_area_cachep, tmp);
+	vm_area_free(tmp);
 fail_nomem:
 	retval = -ENOMEM;
 	vm_unacct_memory(charge);