Sorry to butt in before Jens' review but i have one small comment:
On Fri, Sep 2, 2011 at 5:01 PM, Jan Kara <jack@xxxxxxx> wrote:
> The logic in bdi_forker_thread() is unnecessarily convoluted by setting task
> state there and back or calling schedule_timeout() in TASK_RUNNING state. Also
> clearing of BDI_pending bit is placed at the and of global loop and cases of a
> switch which mustn't reach it must call 'continue' instead of 'break' which is
> non-intuitive and thus asking for trouble. So make the logic more obvious.
>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> CC: consul.kautuk@xxxxxxxxx
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> mm/backing-dev.c | 37 ++++++++++++++++++++-----------------
> 1 files changed, 20 insertions(+), 17 deletions(-)
>
> This should be the right cleanup. Jens?
>
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index d6edf8d..bdf7d6b 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -359,6 +359,17 @@ static unsigned long bdi_longest_inactive(void)
> return max(5UL * 60 * HZ, interval);
> }
>
> +/*
> + * Clear pending bit and wakeup anybody waiting for flusher thread startup
> + * or teardown.
> + */
> +static void bdi_clear_pending(struct backing_dev_info *bdi)
> +{
> + clear_bit(BDI_pending, &bdi->state);
> + smp_mb__after_clear_bit();
> + wake_up_bit(&bdi->state, BDI_pending);
> +}
> +
> static int bdi_forker_thread(void *ptr)
> {
> struct bdi_writeback *me = ptr;
> @@ -390,8 +401,6 @@ static int bdi_forker_thread(void *ptr)
> }
>
> spin_lock_bh(&bdi_lock);
> - set_current_state(TASK_INTERRUPTIBLE);
> -
> list_for_each_entry(bdi, &bdi_list, bdi_list) {
> bool have_dirty_io;
>
> @@ -441,13 +450,8 @@ static int bdi_forker_thread(void *ptr)
> }
> spin_unlock_bh(&bdi_lock);
>
> - /* Keep working if default bdi still has things to do */
> - if (!list_empty(&me->bdi->work_list))
> - __set_current_state(TASK_RUNNING);
> -
> switch (action) {
> case FORK_THREAD:
> - __set_current_state(TASK_RUNNING);
> task = kthread_create(bdi_writeback_thread, &bdi->wb,
> "flush-%s", dev_name(bdi->dev));
> if (IS_ERR(task)) {
> @@ -469,14 +473,21 @@ static int bdi_forker_thread(void *ptr)
> spin_unlock_bh(&bdi->wb_lock);
> wake_up_process(task);
> }
> + bdi_clear_pending(bdi);
> break;
>
> case KILL_THREAD:
> - __set_current_state(TASK_RUNNING);
> kthread_stop(task);
> + bdi_clear_pending(bdi);
> break;
>
> case NO_ACTION:
> + /* Keep working if default bdi still has things to do */
Can we acquire and release the spinlocks as below:
spin_lock_bh(&me->bdi->wb_lock) ;
> + if (!list_empty(&me->bdi->work_list)) {
spin_unlock_bh(&me->bdi->wb_lock) ;
> + try_to_freeze();
> + break;
> + }
> + set_current_state(TASK_INTERRUPTIBLE);
spin_unlock_bh(&me->bdi->wb_lock) ;
> if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
> /*
> * There are no dirty data. The only thing we
> @@ -489,16 +500,8 @@ static int bdi_forker_thread(void *ptr)
> else
> schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
> try_to_freeze();
> - /* Back to the main loop */
> - continue;
> + break;
> }
> -
> - /*
> - * Clear pending bit and wakeup anybody waiting to tear us down.
> - */
> - clear_bit(BDI_pending, &bdi->state);
> - smp_mb__after_clear_bit();
> - wake_up_bit(&bdi->state, BDI_pending);
> }
>
> return 0;
> --
> 1.7.1
>
>
That should take care of the problem I initially mentioned due to the
wakeup_timer_fn executing
in parallel on another CPU as the task state will now be protected by
the wb_lock spinlock.
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