The following commit has been merged into the core/core branch of tip: Commit-ID: be9a2277cafd318976d59c41a7f45a934ec43b26 Gitweb: https://git.kernel.org/tip/be9a2277cafd318976d59c41a7f45a934ec43b26 Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> AuthorDate: Thu, 17 Feb 2022 11:23:59 +01:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Tue, 22 Feb 2022 22:25:01 +01:00 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@xxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Acked-by: Andy Lutomirski <luto@xxxxxxxxxx> Link: https://lore.kernel.org/r/20220217102406.3697941-2-bigeasy@xxxxxxxxxxxxx --- kernel/fork.c | 74 ++++++++++++++++++++++++++------------------------ 1 file changed, 39 insertions(+), 35 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index a024bf6..f5cc101 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; @@ -258,45 +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); + int i; - 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 < 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; - 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; +} - return; - } +# else /* !CONFIG_VMAP_STACK */ - vfree_atomic(tsk->stack); - return; +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; } -#endif + 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
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