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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: 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/20220217102406.3697941-2-bigeasy@linutronix.de
This commit is contained in:
Sebastian Andrzej Siewior 2022-02-17 11:23:59 +01:00 committed by Thomas Gleixner
parent cfb92440ee
commit be9a2277ca
1 changed files with 39 additions and 35 deletions
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74
kernel/fork.c
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@ -185,7 +185,7 @@ static inline void free_task_struct(struct task_struct *tsk)
*/
# if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK)
#ifdef CONFIG_VMAP_STACK
# ifdef CONFIG_VMAP_STACK
/*
* vmalloc() is a bit slow, and calling vfree() enough times will force a TLB
* flush. Try to minimize the number of calls by caching stacks.
@ -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;
@ -258,7 +256,34 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
tsk->stack = stack;
}
return stack;
#else
}
static void free_thread_stack(struct task_struct *tsk)
{
struct vm_struct *vm = task_stack_vm_area(tsk);
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)
continue;
tsk->stack = NULL;
tsk->stack_vm_area = NULL;
return;
}
vfree_atomic(tsk->stack);
tsk->stack = NULL;
tsk->stack_vm_area = NULL;
}
# 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);
@ -267,36 +292,17 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
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)
continue;
return;
}
vfree_atomic(tsk->stack);
return;
}
#endif
__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