[RFC PATCH 04/15] fork: Separate vmap stack allocation and free calls

[Mostafa Saleh]

From: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>

In preparation for the partially populated stacks, separate out the
__vmalloc_node and vfree calls from the vmap based stack allocations.

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>
[Resolved conflict in alloc_thread_stack_node(), update commit msg]
Signed-off-by: Mostafa Saleh <smostafa@xxxxxxxxxx>
---
 kernel/fork.c | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 473878d7f62f..3f1c46d8f7ec 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -272,6 +272,21 @@ 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);
@@ -280,7 +295,7 @@ 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)
@@ -307,7 +322,7 @@ 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;
 	}
 
@@ -336,14 +351,14 @@ 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 offset = 0;
+		void *stack;
 
 		if (memcg_charge_kernel_stack(vm_area)) {
-			vfree(vm_area->addr);
+			free_vmap_stack(vm_area);
 			return -ENOMEM;
 		}
 
@@ -364,15 +379,12 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 		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;
 	}
 	/*
@@ -381,8 +393,7 @@ 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;
 }
 
-- 
2.56.0.rc1.315.gc6ed9934b7-goog