[PATCH v2 04/13] fork: separate vmap stack allocation and free calls

[David Stevens]

From: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>

In preparation for the dynamic stacks, separate out the
__vmalloc_node_range and vfree calls from the vmap based stack
allocations. The dynamic stacks will use their own variants of these
functions.

Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
[Fix a bug in original patch: free_vmap_stack(vm_area->addr)]
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
[Add missing free_vmap_stack conversion, fix typos, rebase]
Signed-off-by: David Stevens <stevensd@xxxxxxxxxx>
---
 kernel/fork.c | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 72c081db492c..8bf32815f422 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -269,6 +269,21 @@ static bool try_release_thread_stack_to_cache(struct vm_struct *vm_area)
 	return false;
 }
 
+static inline struct vm_struct *alloc_vmap_stack(int node)
+{
+	void *stack;
+
+	stack = __vmalloc_node(THREAD_SIZE, THREAD_ALIGN, GFP_VMAP_STACK,
+			       node, __builtin_return_address(0));
+
+	return stack ? find_vm_area(stack) : NULL;
+}
+
+static inline void free_vmap_stack(struct vm_struct *vm_area)
+{
+	vfree(vm_area->addr);
+}
+
 static void thread_stack_free_rcu(struct rcu_head *rh)
 {
 	struct vm_stack *vm_stack = container_of(rh, struct vm_stack, rcu);
@@ -277,7 +292,7 @@ static void thread_stack_free_rcu(struct rcu_head *rh)
 	if (try_release_thread_stack_to_cache(vm_stack->stack_vm_area))
 		return;
 
-	vfree(vm_area->addr);
+	free_vmap_stack(vm_area);
 }
 
 static void thread_stack_delayed_free(struct task_struct *tsk)
@@ -304,7 +319,7 @@ static int free_vm_stack_cache(unsigned int cpu)
 		if (!vm_area)
 			continue;
 
-		vfree(vm_area->addr);
+		free_vmap_stack(vm_area);
 		cached_vm_stack_areas[i] = NULL;
 	}
 
@@ -333,41 +348,35 @@ static int memcg_charge_kernel_stack(struct vm_struct *vm_area)
 static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 {
 	struct vm_struct *vm_area;
-	void *stack;
 
 	vm_area = alloc_thread_stack_node_from_cache(tsk, node);
 	if (vm_area) {
 		unsigned long memset_offset = 0;
 
 		if (memcg_charge_kernel_stack(vm_area)) {
-			vfree(vm_area->addr);
+			free_vmap_stack(vm_area);
 			return -ENOMEM;
 		}
 
 		/* Reset stack metadata. */
 		kasan_unpoison_range(vm_area->addr, THREAD_SIZE);
-
-		stack = kasan_reset_tag(vm_area->addr);
+		tsk->stack = kasan_reset_tag(vm_area->addr);
 
 		/* Clear stale pointers from reused stack. */
 		if (!IS_ENABLED(CONFIG_STACK_GROWSUP))
 			memset_offset = THREAD_SIZE - vm_area->nr_pages * PAGE_SIZE;
-		memset(stack + memset_offset, 0, vm_area->nr_pages * PAGE_SIZE);
+		memset(tsk->stack + memset_offset, 0, vm_area->nr_pages * PAGE_SIZE);
 
 		tsk->stack_vm_area = vm_area;
-		tsk->stack = stack;
 		return 0;
 	}
 
-	stack = __vmalloc_node(THREAD_SIZE, THREAD_ALIGN,
-				     GFP_VMAP_STACK,
-				     node, __builtin_return_address(0));
-	if (!stack)
+	vm_area = alloc_vmap_stack(node);
+	if (!vm_area)
 		return -ENOMEM;
 
-	vm_area = find_vm_area(stack);
 	if (memcg_charge_kernel_stack(vm_area)) {
-		vfree(stack);
+		free_vmap_stack(vm_area);
 		return -ENOMEM;
 	}
 	/*
@@ -376,8 +385,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 	 * so cache the vm_struct.
 	 */
 	tsk->stack_vm_area = vm_area;
-	stack = kasan_reset_tag(stack);
-	tsk->stack = stack;
+	tsk->stack = kasan_reset_tag(vm_area->addr);
 	return 0;
 }
 
-- 
2.54.0.rc2.544.gc7ae2d5bb8-goog