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Date: Tue, 25 Jan 2022 16:26:45 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org
Cc: Andy Lutomirski <luto@...nel.org>, Ben Segall <bsegall@...gle.com>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vincent Guittot <vincent.guittot@...aro.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH 1/8] kernel/fork: Redo ifdefs around task's 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 we 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 that we are currently in.
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 relavant ifdef block.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
kernel/fork.c | 74 +++++++++++++++++++++++++++------------------------
1 file changed, 39 insertions(+), 35 deletions(-)
diff --git a/kernel/fork.c b/kernel/fork.c
index d75a528f7b219..f63c0af6002da 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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
--
2.34.1
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