From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3AE9EC433F5 for ; Thu, 18 Nov 2021 14:35:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 21E31611BF for ; Thu, 18 Nov 2021 14:35:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233396AbhKROi3 (ORCPT ); Thu, 18 Nov 2021 09:38:29 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:39392 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233364AbhKROiB (ORCPT ); Thu, 18 Nov 2021 09:38:01 -0500 From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1637246099; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EWsDuhYwDmjO2QKAYvZZ7cOB40/dUe6Z02V8M2yXQrs=; b=H9FFUm6wIaROitku13XykLHAbS0CP7vequgXVCrcv5XsMbBie5l/eHiX1rt8BMsdCQpkpA svn3VmjyUG6W4OQrAPDDYceuF75/Go2ik7yvwVKFVCmtT3HzbpWgz34rLYZ0TqukXh8cmH JPAdf0HnZhcM0Lu2XP36ZT4MG2Bv94AOODPsnUaTvyCgNCxdbVqzpi7juXSAy+h4niP55H lOlnINzuLnDcy5GlOtFvWqdTsA3Itq96lG7i+wLiB/BsV+jcNtIheyLF1NU6l7M/sBR3jh o09vfP8ovTibhZ303H3nfqUvUFGKiy/ytOITQbceU0jVlkoRsSOaIhFVIl4YaQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1637246099; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EWsDuhYwDmjO2QKAYvZZ7cOB40/dUe6Z02V8M2yXQrs=; b=HINac8iWV8Do0OwTDKkjicINsGeWv+/2yGuxdIZQb062boBr/zLWah1RrF7CjW4KYXr+cH kkLQjBClxxGWzcBw== To: linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org Cc: Ingo Molnar , Peter Zijlstra , Andy Lutomirski , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira , Sebastian Andrzej Siewior Subject: [PATCH 1/8] kernel/fork: Redo ifdefs around task's handling. Date: Thu, 18 Nov 2021 15:34:45 +0100 Message-Id: <20211118143452.136421-2-bigeasy@linutronix.de> In-Reply-To: <20211118143452.136421-1-bigeasy@linutronix.de> References: <20211118143452.136421-1-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- kernel/fork.c | 74 +++++++++++++++++++++++++++------------------------ 1 file changed, 39 insertions(+), 35 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 3244cc56b697d..bb3f2980f94fb 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -184,7 +184,7 @@ static inline void free_task_struct(struct task_struct = *tsk) */ # if THREAD_SIZE >=3D PAGE_SIZE || defined(CONFIG_VMAP_STACK) =20 -#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. @@ -209,11 +209,9 @@ static int free_vm_stack_cache(unsigned int cpu) =20 return 0; } -#endif =20 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int= node) { -#ifdef CONFIG_VMAP_STACK void *stack; int i; =20 @@ -257,7 +255,34 @@ static unsigned long *alloc_thread_stack_node(struct t= ask_struct *tsk, int node) tsk->stack =3D stack; } return stack; -#else +} + +static void free_thread_stack(struct task_struct *tsk) +{ + struct vm_struct *vm =3D task_stack_vm_area(tsk); + int i; + + for (i =3D 0; i < THREAD_SIZE / PAGE_SIZE; i++) + memcg_kmem_uncharge_page(vm->pages[i], 0); + + for (i =3D 0; i < NR_CACHED_STACKS; i++) { + if (this_cpu_cmpxchg(cached_stacks[i], NULL, + tsk->stack_vm_area) !=3D NULL) + continue; + + tsk->stack =3D NULL; + tsk->stack_vm_area =3D NULL; + return; + } + vfree_atomic(tsk->stack); + tsk->stack =3D NULL; + tsk->stack_vm_area =3D NULL; +} + +# else /* !CONFIG_VMAP_STACK */ + +static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int= node) +{ struct page *page =3D alloc_pages_node(node, THREADINFO_GFP, THREAD_SIZE_ORDER); =20 @@ -266,36 +291,17 @@ static unsigned long *alloc_thread_stack_node(struct = task_struct *tsk, int node) return tsk->stack; } return NULL; -#endif } =20 -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 =3D task_stack_vm_area(tsk); - - if (vm) { - int i; - - for (i =3D 0; i < THREAD_SIZE / PAGE_SIZE; i++) - memcg_kmem_uncharge_page(vm->pages[i], 0); - - for (i =3D 0; i < NR_CACHED_STACKS; i++) { - if (this_cpu_cmpxchg(cached_stacks[i], - NULL, tsk->stack_vm_area) !=3D NULL) - continue; - - return; - } - - vfree_atomic(tsk->stack); - return; - } -#endif - __free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER); + tsk->stack =3D NULL; } -# else + +# endif /* CONFIG_VMAP_STACK */ +# else /* !(THREAD_SIZE >=3D PAGE_SIZE || defined(CONFIG_VMAP_STACK)) */ + static struct kmem_cache *thread_stack_cache; =20 static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, @@ -311,6 +317,7 @@ static unsigned long *alloc_thread_stack_node(struct ta= sk_struct *tsk, static void free_thread_stack(struct task_struct *tsk) { kmem_cache_free(thread_stack_cache, tsk->stack); + tsk->stack =3D NULL; } =20 void thread_stack_cache_init(void) @@ -320,8 +327,9 @@ void thread_stack_cache_init(void) THREAD_SIZE, NULL); BUG_ON(thread_stack_cache =3D=3D NULL); } -# endif -#endif + +# endif /* THREAD_SIZE >=3D PAGE_SIZE || defined(CONFIG_VMAP_STACK) */ +#endif /* !CONFIG_ARCH_THREAD_STACK_ALLOCATOR */ =20 /* SLAB cache for signal_struct structures (tsk->signal) */ static struct kmem_cache *signal_cachep; @@ -429,10 +437,6 @@ static void release_task_stack(struct task_struct *tsk) =20 account_kernel_stack(tsk, -1); free_thread_stack(tsk); - tsk->stack =3D NULL; -#ifdef CONFIG_VMAP_STACK - tsk->stack_vm_area =3D NULL; -#endif } =20 #ifdef CONFIG_THREAD_INFO_IN_TASK --=20 2.33.1