fork: Don't assign the stack pointer in dup_task_struct()

All four versions of alloc_thread_stack_node() assign now
task_struct::stack in case the allocation was successful.

Let alloc_thread_stack_node() return an error code instead of the stack
pointer and remove the stack assignment in dup_task_struct().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20220217102406.3697941-5-bigeasy@linutronix.de

diff --git a/kernel/fork.c b/kernel/fork.c
index 7b70c47..875bd43 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -211,7 +211,7 @@ static int free_vm_stack_cache(unsigned int cpu)
        return 0;
 }
 
-static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 {
        void *stack;
        int i;
@@ -232,7 +232,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 
                tsk->stack_vm_area = s;
                tsk->stack = s->addr;
-               return s->addr;
+               return 0;
        }
 
        /*
@@ -245,17 +245,16 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
                                     THREADINFO_GFP & ~__GFP_ACCOUNT,
                                     PAGE_KERNEL,
                                     0, node, __builtin_return_address(0));
-
+       if (!stack)
+               return -ENOMEM;
        /*
         * We can't call find_vm_area() in interrupt context, and
         * free_thread_stack() can be called in interrupt context,
         * so cache the vm_struct.
         */
-       if (stack) {
-               tsk->stack_vm_area = find_vm_area(stack);
-               tsk->stack = stack;
-       }
-       return stack;
+       tsk->stack_vm_area = find_vm_area(stack);
+       tsk->stack = stack;
+       return 0;
 }
 
 static void free_thread_stack(struct task_struct *tsk)
@@ -282,16 +281,16 @@ static void free_thread_stack(struct task_struct *tsk)
 
 #  else /* !CONFIG_VMAP_STACK */
 
-static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 {
        struct page *page = alloc_pages_node(node, THREADINFO_GFP,
                                             THREAD_SIZE_ORDER);
 
        if (likely(page)) {
                tsk->stack = kasan_reset_tag(page_address(page));
-               return tsk->stack;
+               return 0;
        }
-       return NULL;
+       return -ENOMEM;
 }
 
 static void free_thread_stack(struct task_struct *tsk)
@@ -305,14 +304,13 @@ static void free_thread_stack(struct task_struct *tsk)
 
 static struct kmem_cache *thread_stack_cache;
 
-static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
-                                                 int node)
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 {
        unsigned long *stack;
        stack = kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
        stack = kasan_reset_tag(stack);
        tsk->stack = stack;
-       return stack;
+       return stack ? 0 : -ENOMEM;
 }
 
 static void free_thread_stack(struct task_struct *tsk)
@@ -332,13 +330,13 @@ void thread_stack_cache_init(void)
 # endif /* THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK) */
 #else /* CONFIG_ARCH_THREAD_STACK_ALLOCATOR */
 
-static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
+static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 {
        unsigned long *stack;
 
        stack = arch_alloc_thread_stack_node(tsk, node);
        tsk->stack = stack;
-       return stack;
+       return stack ? 0 : -ENOMEM;
 }
 
 static void free_thread_stack(struct task_struct *tsk)
@@ -895,8 +893,6 @@ void set_task_stack_end_magic(struct task_struct *tsk)
 static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 {
        struct task_struct *tsk;
-       unsigned long *stack;
-       struct vm_struct *stack_vm_area __maybe_unused;
        int err;
 
        if (node == NUMA_NO_NODE)
@@ -909,24 +905,13 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
        if (err)
                goto free_tsk;
 
-       stack = alloc_thread_stack_node(tsk, node);
-       if (!stack)
+       err = alloc_thread_stack_node(tsk, node);
+       if (err)
                goto free_tsk;
 
        if (memcg_charge_kernel_stack(tsk))
                goto free_stack;
 
-       stack_vm_area = task_stack_vm_area(tsk);
-
-       /*
-        * arch_dup_task_struct() clobbers the stack-related fields.  Make
-        * sure they're properly initialized before using any stack-related
-        * functions again.
-        */
-       tsk->stack = stack;
-#ifdef CONFIG_VMAP_STACK
-       tsk->stack_vm_area = stack_vm_area;
-#endif
 #ifdef CONFIG_THREAD_INFO_IN_TASK
        refcount_set(&tsk->stack_refcount, 1);
 #endif