Re: [Bug #14388] keyboard under X with 2.6.31

Boyan
2009-10-14T19:59:41Z

Linus Torvalds wrote:
>
> On Wed, 14 Oct 2009, Linus Torvalds wrote:
>> But it's certainly true that it just never happened before. At least for
>> the !low_latency case, I'm not so sure about the low_latency=1 case, but I
>> haven't checked either - it would depend on any higher-level
>> serialization.
>
> Btw, we _could_ try to solve this by adding some workqueue function to
> "run delayed work now", and then always doing the 'flush_to_ldisc()'
> through the workqueue logic.
>
> So this is an "alternate patch": instead of making flush_to_ldisc() be
> safe to re-enter, we try to make sure it's always called through the whole
> workqueue logic and thus serialized by that.
>
> Of course, keventd itself is multi-threaded, so I'm not entirely sure even
> -that- guarantees that one 'flush_to_ldisc()' couldn't be pending on one
> CPU while it is then scheduled and then run on another CPU concurrently
> too. The WORK_STRUCT_PENDING bit guarantees exclusion from the lists and
> from being pending, but the work might be both pending and _running_ at
> the same time, afaik.
>
> I'm adding Oleg to the Cc, because he's the workqueue-master. Oleg?
>
> The patch below is - surprise, surprise - entirely untested. I'm not sure
> my 'flush_delayed_work()' implementation is entirely kosher. But it looks
> like it might work, and it did compile for me (technically this is on top
> of my flush_to_ldisc() patch, but they should be independent of each
> other).
>
> Linus
>
> ---
> drivers/char/tty_buffer.c | 2 +-
> include/linux/workqueue.h | 1 +
> kernel/workqueue.c | 18 ++++++++++++++++++
> 3 files changed, 20 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
> index 0296612..66fa4e1 100644
> --- a/drivers/char/tty_buffer.c
> +++ b/drivers/char/tty_buffer.c
> @@ -468,7 +468,7 @@ static void flush_to_ldisc(struct work_struct *work)
> */
> void tty_flush_to_ldisc(struct tty_struct *tty)
> {
> - flush_to_ldisc(&tty->buf.work.work);
> + flush_delayed_work(&tty->buf.work);
> }
>
> /**
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index 7ef0c7b..cf24c20 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -207,6 +207,7 @@ extern int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
>
> extern void flush_workqueue(struct workqueue_struct *wq);
> extern void flush_scheduled_work(void);
> +extern void flush_delayed_work(struct delayed_work *work);
>
> extern int schedule_work(struct work_struct *work);
> extern int schedule_work_on(int cpu, struct work_struct *work);
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index addfe2d..ccefe57 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -640,6 +640,24 @@ int schedule_delayed_work(struct delayed_work *dwork,
> EXPORT_SYMBOL(schedule_delayed_work);
>
> /**
> + * flush_delayed_work - block until a dwork_struct's callback has terminated
> + * @dwork: the delayed work which is to be flushed
> + *
> + * Any timeout is cancelled, and any pending work is run immediately.
> + */
> +void flush_delayed_work(struct delayed_work *dwork)
> +{
> + if (del_timer(&dwork->timer)) {
> + struct cpu_workqueue_struct *cwq;
> + cwq = wq_per_cpu(keventd_wq, get_cpu());
> + __queue_work(cwq, &dwork->work);
> + put_cpu();
> + }
> + flush_work(&dwork->work);
> +}
> +EXPORT_SYMBOL(flush_delayed_work);
> +
> +/**
> * schedule_delayed_work_on - queue work in global workqueue on CPU after delay
> * @cpu: cpu to use
> * @dwork: job to be done
>

Works for me. I couldn't reproduce the problem with only this patch on
top of 2.6.31.4.