Commit be9a2277 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Thomas Gleixner
Browse files

fork: Redo ifdefs around task stack handling 



The use of ifdef CONFIG_VMAP_STACK is confusing in terms what is
actually happenning and what can happen.

For instance from reading free_thread_stack() it appears that in the
CONFIG_VMAP_STACK case it may receive a non-NULL vm pointer but it may also
be NULL in which case __free_pages() is used to free the stack.  This is
however not the case because in the VMAP case a non-NULL pointer is always
returned here.  Since it looks like this might happen, the compiler creates
the correct dead code with the invocation to __free_pages() and everything
around it. Twice.

Add spaces between the ifdef and the identifer to recognize the ifdef
level which is currently in scope.

Add the current identifer as a comment behind #else and #endif.
Move the code within free_thread_stack() and alloc_thread_stack_node()
into the relevant ifdef blocks.

Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20220217102406.3697941-2-bigeasy@linutronix.de
parent cfb92440

kernel/fork.c

+39 −35
Original line number Diff line number Diff line
@@ -210,11 +210,9 @@ static int free_vm_stack_cache(unsigned int cpu) 


	return 0;

}

#endif



static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)

{

#ifdef CONFIG_VMAP_STACK

	void *stack;

	int i;
@@ -258,45 +256,53 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) 
		tsk->stack = stack;

	}

	return stack;

#else

	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 NULL;

#endif

}



static inline void free_thread_stack(struct task_struct *tsk)

static void free_thread_stack(struct task_struct *tsk)

{

#ifdef CONFIG_VMAP_STACK

	struct vm_struct *vm = task_stack_vm_area(tsk);



	if (vm) {

	int i;



	for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++)

		memcg_kmem_uncharge_page(vm->pages[i], 0);



	for (i = 0; i < NR_CACHED_STACKS; i++) {

			if (this_cpu_cmpxchg(cached_stacks[i],

					NULL, tsk->stack_vm_area) != NULL)

		if (this_cpu_cmpxchg(cached_stacks[i], NULL,

				     tsk->stack_vm_area) != NULL)

			continue;



		tsk->stack = NULL;

		tsk->stack_vm_area = NULL;

		return;

	}



	vfree_atomic(tsk->stack);

		return;

	tsk->stack = NULL;

	tsk->stack_vm_area = NULL;

}

#endif



#  else /* !CONFIG_VMAP_STACK */



static unsigned long *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 NULL;

}



static void free_thread_stack(struct task_struct *tsk)

{

	__free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER);

	tsk->stack = NULL;

}

# else



#  endif /* CONFIG_VMAP_STACK */

# else /* !(THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)) */



static struct kmem_cache *thread_stack_cache;



static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
@@ -312,6 +318,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, 
static void free_thread_stack(struct task_struct *tsk)

{

	kmem_cache_free(thread_stack_cache, tsk->stack);

	tsk->stack = NULL;

}



void thread_stack_cache_init(void)
@@ -321,8 +328,9 @@ void thread_stack_cache_init(void) 
					THREAD_SIZE, NULL);

	BUG_ON(thread_stack_cache == NULL);

}

# endif

#endif



# endif /* THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK) */

#endif /* !CONFIG_ARCH_THREAD_STACK_ALLOCATOR */



/* SLAB cache for signal_struct structures (tsk->signal) */

static struct kmem_cache *signal_cachep;
@@ -432,10 +440,6 @@ static void release_task_stack(struct task_struct *tsk) 


	account_kernel_stack(tsk, -1);

	free_thread_stack(tsk);

	tsk->stack = NULL;

#ifdef CONFIG_VMAP_STACK

	tsk->stack_vm_area = NULL;

#endif

}



#ifdef CONFIG_THREAD_INFO_IN_TASK