From c65eacbe290b8141554c71b2c94489e73ade8c8d Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Tue, 13 Sep 2016 14:29:24 -0700 Subject: sched/core: Allow putting thread_info into task_struct If an arch opts in by setting CONFIG_THREAD_INFO_IN_TASK_STRUCT, then thread_info is defined as a single 'u32 flags' and is the first entry of task_struct. thread_info::task is removed (it serves no purpose if thread_info is embedded in task_struct), and thread_info::cpu gets its own slot in task_struct. This is heavily based on a patch written by Linus. Originally-from: Linus Torvalds Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Jann Horn Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/a0898196f0476195ca02713691a5037a14f2aac5.1473801993.git.luto@kernel.org Signed-off-by: Ingo Molnar --- include/linux/init_task.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'include/linux/init_task.h') diff --git a/include/linux/init_task.h b/include/linux/init_task.h index f8834f820ec2..9c04d44eeb3c 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -15,6 +15,8 @@ #include #include +#include + #ifdef CONFIG_SMP # define INIT_PUSHABLE_TASKS(tsk) \ .pushable_tasks = PLIST_NODE_INIT(tsk.pushable_tasks, MAX_PRIO), @@ -183,12 +185,19 @@ extern struct task_group root_task_group; # define INIT_KASAN(tsk) #endif +#ifdef CONFIG_THREAD_INFO_IN_TASK +# define INIT_TASK_TI(tsk) .thread_info = INIT_THREAD_INFO(tsk), +#else +# define INIT_TASK_TI(tsk) +#endif + /* * INIT_TASK is used to set up the first task table, touch at * your own risk!. Base=0, limit=0x1fffff (=2MB) */ #define INIT_TASK(tsk) \ { \ + INIT_TASK_TI(tsk) \ .state = 0, \ .stack = init_stack, \ .usage = ATOMIC_INIT(2), \ -- cgit v1.2.3 From 68f24b08ee892d47bdef925d676e1ae1ccc316f8 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 15 Sep 2016 22:45:48 -0700 Subject: sched/core: Free the stack early if CONFIG_THREAD_INFO_IN_TASK We currently keep every task's stack around until the task_struct itself is freed. This means that we keep the stack allocation alive for longer than necessary and that, under load, we free stacks in big batches whenever RCU drops the last task reference. Neither of these is good for reuse of cache-hot memory, and freeing in batches prevents us from usefully caching small numbers of vmalloced stacks. On architectures that have thread_info on the stack, we can't easily change this, but on architectures that set THREAD_INFO_IN_TASK, we can free it as soon as the task is dead. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Jann Horn Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/08ca06cde00ebed0046c5d26cbbf3fbb7ef5b812.1474003868.git.luto@kernel.org Signed-off-by: Ingo Molnar --- include/linux/init_task.h | 4 +++- include/linux/sched.h | 14 ++++++++++++++ kernel/fork.c | 35 ++++++++++++++++++++++++++++++++++- kernel/sched/core.c | 4 ++++ 4 files changed, 55 insertions(+), 2 deletions(-) (limited to 'include/linux/init_task.h') diff --git a/include/linux/init_task.h b/include/linux/init_task.h index 9c04d44eeb3c..325f649d77ff 100644 --- a/include/linux/init_task.h +++ b/include/linux/init_task.h @@ -186,7 +186,9 @@ extern struct task_group root_task_group; #endif #ifdef CONFIG_THREAD_INFO_IN_TASK -# define INIT_TASK_TI(tsk) .thread_info = INIT_THREAD_INFO(tsk), +# define INIT_TASK_TI(tsk) \ + .thread_info = INIT_THREAD_INFO(tsk), \ + .stack_refcount = ATOMIC_INIT(1), #else # define INIT_TASK_TI(tsk) #endif diff --git a/include/linux/sched.h b/include/linux/sched.h index a95867267e9f..abb795afc823 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1936,6 +1936,10 @@ struct task_struct { #ifdef CONFIG_VMAP_STACK struct vm_struct *stack_vm_area; #endif +#ifdef CONFIG_THREAD_INFO_IN_TASK + /* A live task holds one reference. */ + atomic_t stack_refcount; +#endif /* CPU-specific state of this task */ struct thread_struct thread; /* @@ -3143,12 +3147,22 @@ static inline unsigned long *end_of_stack(struct task_struct *p) #endif +#ifdef CONFIG_THREAD_INFO_IN_TASK +static inline void *try_get_task_stack(struct task_struct *tsk) +{ + return atomic_inc_not_zero(&tsk->stack_refcount) ? + task_stack_page(tsk) : NULL; +} + +extern void put_task_stack(struct task_struct *tsk); +#else static inline void *try_get_task_stack(struct task_struct *tsk) { return task_stack_page(tsk); } static inline void put_task_stack(struct task_struct *tsk) {} +#endif #define task_stack_end_corrupted(task) \ (*(end_of_stack(task)) != STACK_END_MAGIC) diff --git a/kernel/fork.c b/kernel/fork.c index 0c240fd5beba..5dd0a516626d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -269,11 +269,40 @@ static void account_kernel_stack(struct task_struct *tsk, int account) } } -void free_task(struct task_struct *tsk) +static void release_task_stack(struct task_struct *tsk) { account_kernel_stack(tsk, -1); arch_release_thread_stack(tsk->stack); free_thread_stack(tsk); + tsk->stack = NULL; +#ifdef CONFIG_VMAP_STACK + tsk->stack_vm_area = NULL; +#endif +} + +#ifdef CONFIG_THREAD_INFO_IN_TASK +void put_task_stack(struct task_struct *tsk) +{ + if (atomic_dec_and_test(&tsk->stack_refcount)) + release_task_stack(tsk); +} +#endif + +void free_task(struct task_struct *tsk) +{ +#ifndef CONFIG_THREAD_INFO_IN_TASK + /* + * The task is finally done with both the stack and thread_info, + * so free both. + */ + release_task_stack(tsk); +#else + /* + * If the task had a separate stack allocation, it should be gone + * by now. + */ + WARN_ON_ONCE(atomic_read(&tsk->stack_refcount) != 0); +#endif rt_mutex_debug_task_free(tsk); ftrace_graph_exit_task(tsk); put_seccomp_filter(tsk); @@ -411,6 +440,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) #ifdef CONFIG_VMAP_STACK tsk->stack_vm_area = stack_vm_area; #endif +#ifdef CONFIG_THREAD_INFO_IN_TASK + atomic_set(&tsk->stack_refcount, 1); +#endif if (err) goto free_stack; @@ -1771,6 +1803,7 @@ bad_fork_cleanup_count: atomic_dec(&p->cred->user->processes); exit_creds(p); bad_fork_free: + put_task_stack(p); free_task(p); fork_out: return ERR_PTR(retval); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0b6238f18da2..23c6037e2d89 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2772,6 +2772,10 @@ static struct rq *finish_task_switch(struct task_struct *prev) * task and put them back on the free list. */ kprobe_flush_task(prev); + + /* Task is done with its stack. */ + put_task_stack(prev); + put_task_struct(prev); } -- cgit v1.2.3