Re: [PATCH] rtmutex.c: Fix incorrect waiter check

[Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@hp.com>]

Yes, agreed.  Using the macro (), as done in the patch, is the correct
way to avoid invalid pointer dereferencing.

Tested with patch-3.14.25-rt22 patch on a 2 socket platform.

Reviewed-by: T Makphaibulchoke <tmac@hp.cojm>
Tested-by: T Makphaibulchoke <tmac@hp.cojm>


On 12/05/2014 12:35 PM, Brad Mouring wrote:
> In task_blocks_on_lock, there's a null check on pi_blocked_on
> of the task_struct. This pointer can encode the fact that the
> task that contains the pointer is waking (preventing requeuing)
> and therefore is non-null. Use the inline function to avoid
> dereferencing an invalid "pointer"
> 
> Signed-off-by: Brad Mouring <brad.mouring@ni.com>
> Reported-by: Ben Shelton <ben.shelton@ni.com>
> ---
>  kernel/locking/rtmutex.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 6c40660..535321e 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -335,7 +335,8 @@ int max_lock_depth = 1024;
>  
>  static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
>  {
> -	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
> +	return rt_mutex_real_waiter(p->pi_blocked_on) ?
> +		p->pi_blocked_on->lock : NULL;
>  }
>  
>  /*
>