linux-kernel - Re: [PATCH] rcuperf: Do not wake up shutdown wait queue if "shutdown" is false.

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Message-ID: <20160207194302.GX6719@linux.vnet.ibm.com>
Date:	Sun, 7 Feb 2016 11:43:02 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Artem Savkov <artem.savkov@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcuperf: Do not wake up shutdown wait queue if
 "shutdown" is false.

On Sun, Feb 07, 2016 at 01:31:39PM +0100, Artem Savkov wrote:
> After finishing it's tests rcuperf tries to wake up shutdown_wq even if
> "shutdown" param is set to false, resulting in a wake_up() call on an
> unitialized wait_queue_head_t which leads to "BUG: spinlock bad magic" and
> "BUG: unable to handle kernel NULL pointer dereference".
> 
> Fix by checking "shutdown" param before waking up the queue.
> 
> Signed-off-by: Artem Savkov <artem.savkov@...il.com>

Good catch!  Queued for testing and review.

								Thanx, Paul

> ---
>  kernel/rcu/rcuperf.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/rcu/rcuperf.c b/kernel/rcu/rcuperf.c
> index 09ffa36..fb45a26 100644
> --- a/kernel/rcu/rcuperf.c
> +++ b/kernel/rcu/rcuperf.c
> @@ -414,8 +414,10 @@ rcu_perf_writer(void *arg)
>  					b_rcu_perf_writer_finished =
>  						cur_ops->completed();
>  				}
> -				smp_mb(); /* Assign before wake. */
> -				wake_up(&shutdown_wq);
> +				if (shutdown) {
> +					smp_mb(); /* Assign before wake. */
> +					wake_up(&shutdown_wq);
> +				}
>  			}
>  		}
>  		if (done && !alldone &&
> -- 
> 2.7.0
>