On Fri, 25 Jun 2010 16:20:27 -0500
Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx> wrote:
> [Necessary to make 2.6.35-rc3 not deadlock. Not sure if this is the "right"(tm)
> fix]
>
> The last change to improve the scalability moved the actual wake-up out of
> the section that is protected by spin_lock(sma->sem_perm.lock).
>
> This means that IN_WAKEUP can be in queue.status even when the spinlock is
> acquired by the current task. Thus the same loop that is performed when
> queue.status is read without the spinlock acquired must be performed when
> the spinlock is acquired.
>
> Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Hmm, I'm sorry if I don't understand the code...
>
> ---
> ipc/sem.c | 36 ++++++++++++++++++++++++++++++------
> 1 files changed, 30 insertions(+), 6 deletions(-)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index 506c849..523665f 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1256,6 +1256,32 @@ out:
> return un;
> }
>
> +
> +/** get_queue_result - Retrieve the result code from sem_queue
> + * @q: Pointer to queue structure
> + *
> + * The function retrieve the return code from the pending queue. If
> + * IN_WAKEUP is found in q->status, then we must loop until the value
> + * is replaced with the final value: This may happen if a task is
> + * woken up by an unrelated event (e.g. signal) and in parallel the task
> + * is woken up by another task because it got the requested semaphores.
> + *
> + * The function can be called with or without holding the semaphore spinlock.
> + */
> +static int get_queue_result(struct sem_queue *q)
> +{
> + int error;
> +
> + error = q->status;
> + while(unlikely(error == IN_WAKEUP)) {
> + cpu_relax();
> + error = q->status;
> + }
> +
> + return error;
> +}
no memory barrier is required ?
Thanks,
-Kame
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