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SubjectRe: [PATCH 2/4] rtmutex: add BUG_ON if a task attempts to block on two locks
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On Fri, 2010-07-09 at 15:32 -0700, Darren Hart wrote:
> rtmutex proxy locking complicates the logic a bit and opens up
> the possibility for a task to wake and attempt to take another
> sleeping lock without knowing it has been enqueued on another
> lock already. Add a BUG_ON to catch this scenario early.
>
> Signed-off-by: Darren Hart <dvhltc@us.ibm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: John Kacur <jkacur@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Mike Galbraith <efault@gmx.de>
> ---
> kernel/rtmutex.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
> index baac7d9..22f9d18 100644
> --- a/kernel/rtmutex.c
> +++ b/kernel/rtmutex.c
> @@ -459,6 +459,9 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
> top_waiter = rt_mutex_top_waiter(lock);
> plist_add(&waiter->list_entry, &lock->wait_list);
>
> + /* Tasks can only block on one lock at a time. */
> + BUG_ON(task->pi_blocked_on != NULL);

WARN_ON may be better. Since it may not cause a system crash or other
huge bug if it is not true.

-- Steve

> +
> task->pi_blocked_on = waiter;
>
> raw_spin_unlock(&task->pi_lock);




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