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Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning

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On Wed 12-10-16 10:57:03, Catalin Marinas wrote:
> Commit 68f24b08ee89 ("sched/core: Free the stack early if
> CONFIG_THREAD_INFO_IN_TASK") may cause the task->stack to be freed
> during kmemleak_scan() execution, leading to either a NULL pointer
> fault (if task->stack is NULL) or kmemleak accessing already freed
> memory. This patch uses the new try_get_task_stack() API to ensure that
> the task stack is not freed during kmemleak stack scanning.

Looks good to me
 
> Fixes: 68f24b08ee89 ("sched/core: Free the stack early if CONFIG_THREAD_INFO_IN_TASK")
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: CAI Qian <caiqian@redhat.com>
> Reported-by: CAI Qian <caiqian@redhat.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> 
> This was reported in a subsequent comment here:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=173901
> 
> However, the original bugzilla entry doesn't look related to task stack
> freeing as it was first reported on 4.8-rc8. Andy, sorry for cc'ing you
> to bugzilla, please feel free to remove your email from the bug above (I
> can't seem to be able to do it).
> 
>  mm/kmemleak.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index a5e453cf05c4..e5355a5b423f 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1453,8 +1453,11 @@ static void kmemleak_scan(void)
>  
>  		read_lock(&tasklist_lock);
>  		do_each_thread(g, p) {
> -			scan_block(task_stack_page(p), task_stack_page(p) +
> -				   THREAD_SIZE, NULL);
> +			void *stack = try_get_task_stack(p);
> +			if (stack) {
> +				scan_block(stack, stack + THREAD_SIZE, NULL);
> +				put_task_stack(p);
> +			}
>  		} while_each_thread(g, p);
>  		read_unlock(&tasklist_lock);
>  	}
> 
> --
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-- 
Michal Hocko
SUSE Labs

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[PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning Catalin Marinas <catalin.marinas@arm.com> - 2016-10-12 12:00 +0200
  Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed during scanning "Hillf Danton" <hillf.zj@alibaba-inc.com> - 2016-10-12 12:30 +0200
    Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning Catalin Marinas <catalin.marinas@arm.com> - 2016-10-12 12:50 +0200
  Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning Michal Hocko <mhocko@kernel.org> - 2016-10-12 12:50 +0200
  Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning Catalin Marinas <catalin.marinas@arm.com> - 2016-10-12 18:20 +0200
  Re: [PATCH] mm: kmemleak: Ensure that the task stack is not freed  during scanning CAI Qian <caiqian@redhat.com> - 2016-10-12 18:40 +0200

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