From: Michal Hocko <mhocko@kernel.org>
To: Hoeun Ryu <hoeun.ryu@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>,
Kees Cook <keescook@chromium.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Mateusz Guzik <mguzik@redhat.com>,
linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com
Subject: Re: [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline
Date: Thu, 9 Feb 2017 09:38:25 +0100 [thread overview]
Message-ID: <20170209083825.GB10257@dhcp22.suse.cz> (raw)
In-Reply-To: <1486613040-30555-1-git-send-email-hoeun.ryu@gmail.com>
On Thu 09-02-17 13:03:46, Hoeun Ryu wrote:
> 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.
>
> Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com>
> ---
> Changes in v2:
> remove cpuhp callback for `starup`, only `teardown` callback is installed.
>
> kernel/fork.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 61284d8..7911ed2 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -170,6 +170,22 @@ void __weak arch_release_thread_stack(unsigned long *stack)
> static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
> #endif
>
> +static int free_vm_stack_cache(unsigned int cpu)
> +{
> + int i;
> +
> + for (i = 0; i < NR_CACHED_STACKS; i++) {
> + struct vm_struct *vm_stack = this_cpu_read(cached_stacks[i]);
the callbak will run on the given cpu so this_cpu_read will be in fact
per_cpu_ptr(cached_stacks[i], cpu). Using this_cpu_read is just too
confusing. Also you do want to make this function defined only for
CONFIG_VMAP_STACK.
> + if (!vm_stack)
> + continue;
> +
> + vfree(vm_stack->addr);
> + this_cpu_write(cached_stacks[i], NULL);
> + }
> +
> + return 0;
> +}
> +
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-02-09 8:54 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-09 4:03 [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline Hoeun Ryu
2017-02-09 4:03 ` [PATCH v2 2/2] fork: make number of cached stacks (vmapped) configurable using Kbuild Hoeun Ryu
2017-02-09 4:26 ` [kernel-hardening] " Eric Biggers
2017-02-09 8:40 ` Michal Hocko
2017-02-09 13:36 ` Hoeun Ryu
2017-02-09 4:22 ` [kernel-hardening] [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline Eric Biggers
2017-02-09 13:35 ` Hoeun Ryu
2017-02-09 7:28 ` kbuild test robot
2017-02-09 8:01 ` kbuild test robot
2017-02-09 8:38 ` Michal Hocko [this message]
2017-02-09 13:36 ` Hoeun Ryu
2017-02-09 10:26 ` kbuild test robot
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