From 19659c59af52df22d1b85208a2c37b2d46290541 Mon Sep 17 00:00:00 2001 From: Hoeun Ryu Date: Mon, 8 May 2017 15:56:11 -0700 Subject: [PATCH] fork: free vmapped stacks in cache when cpus are offline Using virtually mapped stack, kernel stacks are allocated via vmalloc. In the current implementation, two stacks per cpu can be cached when tasks are freed and the cached stacks are used again in task duplications. But the cached stacks may remain unfreed even when cpu are offline. By adding a cpu hotplug callback to free the cached stacks when a cpu goes offline, the pages of the cached stacks are not wasted. Link: http://lkml.kernel.org/r/1487076043-17802-1-git-send-email-hoeun.ryu@gmail.com Signed-off-by: Hoeun Ryu Reviewed-by: Thomas Gleixner Acked-by: Michal Hocko Cc: Ingo Molnar Cc: Andy Lutomirski Cc: Kees Cook Cc: "Eric W. Biederman" Cc: Oleg Nesterov Cc: Mateusz Guzik Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index dd5a371c392a..55e325f4b457 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -179,6 +179,24 @@ void __weak arch_release_thread_stack(unsigned long *stack) */ #define NR_CACHED_STACKS 2 static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]); + +static int free_vm_stack_cache(unsigned int cpu) +{ + struct vm_struct **cached_vm_stacks = per_cpu_ptr(cached_stacks, cpu); + int i; + + for (i = 0; i < NR_CACHED_STACKS; i++) { + struct vm_struct *vm_stack = cached_vm_stacks[i]; + + if (!vm_stack) + continue; + + vfree(vm_stack->addr); + cached_vm_stacks[i] = NULL; + } + + return 0; +} #endif static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) @@ -467,6 +485,11 @@ void __init fork_init(void) for (i = 0; i < UCOUNT_COUNTS; i++) { init_user_ns.ucount_max[i] = max_threads/2; } + +#ifdef CONFIG_VMAP_STACK + cpuhp_setup_state(CPUHP_BP_PREPARE_DYN, "fork:vm_stack_cache", + NULL, free_vm_stack_cache); +#endif } int __weak arch_dup_task_struct(struct task_struct *dst,