Re: [PATCH 1/4] rtmutex: avoid null derefence in WARN_ON

[Steven Rostedt]

On Fri, 2010-07-09 at 15:32 -0700, Darren Hart wrote:
> If the pi_blocked_on variable is NULL, the subsequent WARN_ON's
> will cause an OOPS. Only perform the susequent checks if
> pi_blocked_on is valid.
> 
> Signed-off-by: Darren Hart <dvhltc@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxx>
> Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Cc: John Kacur <jkacur@xxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Mike Galbraith <efault@xxxxxx>
> ---
>  kernel/rtmutex.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
> index 23dd443..baac7d9 100644
> --- a/kernel/rtmutex.c
> +++ b/kernel/rtmutex.c
> @@ -579,9 +579,10 @@ static void wakeup_next_waiter(struct rt_mutex *lock, int savestate)
>  
>  	raw_spin_lock(&pendowner->pi_lock);
>  
> -	WARN_ON(!pendowner->pi_blocked_on);
> -	WARN_ON(pendowner->pi_blocked_on != waiter);
> -	WARN_ON(pendowner->pi_blocked_on->lock != lock);
> +	if (!WARN_ON(!pendowner->pi_blocked_on)) {
> +		WARN_ON(pendowner->pi_blocked_on != waiter);

The above actually has no issue if the pi_blocked_on is NULL.

The below, well yeah.

-- Steve

> +		WARN_ON(pendowner->pi_blocked_on->lock != lock);
> +	}
>  
>  	pendowner->pi_blocked_on = NULL;
>  


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