Re: [PATCH v3 3/3] sched: BUG when stack end location is over written

[Michael Ellerman <mpe@ellerman.id.au>]

On Thu, 2014-09-11 at 16:41 +0100, Aaron Tomlin wrote:
> Currently in the event of a stack overrun a call to schedule()
> does not check for this type of corruption. This corruption is
> often silent and can go unnoticed. However once the corrupted
> region is examined at a later stage, the outcome is undefined
> and often results in a sporadic page fault which cannot be
> handled.
> 
> This patch checks for a stack overrun and takes appropriate
> action since the damage is already done, there is no point
> in continuing.
> 
> Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
> ---
>  kernel/sched/core.c |  3 +++
>  lib/Kconfig.debug   | 12 ++++++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ec1a286..0b70b73 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2660,6 +2660,9 @@ static noinline void __schedule_bug(struct task_struct *prev)
>   */
>  static inline void schedule_debug(struct task_struct *prev)
>  {
> +#ifdef CONFIG_SCHED_STACK_END_CHECK
> +	BUG_ON(unlikely(task_stack_end_corrupted(prev)))
> +#endif

Spot the bug? Please compile your code in future.


../kernel/sched/core.c: In function ‘schedule_debug’:
../kernel/sched/core.c:2671:2: error: expected ‘;’ before ‘if’
  if (unlikely(in_atomic_preempt_off() && prev->state != TASK_DEAD))
  ^
../kernel/sched/core.c: At top level:
../kernel/sched/core.c:2635:22: warning: ‘__schedule_bug’ defined but not used [-Wunused-function]
 static noinline void __schedule_bug(struct task_struct *prev)
                      ^
make[3]: *** [kernel/sched/core.o] Error 1
make[2]: *** [kernel/sched] Error 2
make[1]: *** [kernel] Error 2
make: *** [sub-make] Error 2


cheers