On Wed, Nov 23, 2016 at 01:41:45PM +1100, NeilBrown wrote:
> On Tue, Nov 22 2016, Shaohua Li wrote:
>
> > There is mechanism to suspend a kernel thread. Use it instead of playing
> > create/destroy game.
>
> Good idea!
>
> >
> > Signed-off-by: Shaohua Li <shli@xxxxxx>
> > ---
> > drivers/md/md.c | 4 +++-
> > drivers/md/raid5-cache.c | 18 +++++-------------
> > 2 files changed, 8 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index d3cef77..f548469 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -7136,10 +7136,12 @@ static int md_thread(void *arg)
> > wait_event_interruptible_timeout
> > (thread->wqueue,
> > test_bit(THREAD_WAKEUP, &thread->flags)
> > - || kthread_should_stop(),
> > + || kthread_should_stop() || kthread_should_park(),
> > thread->timeout);
> >
> > clear_bit(THREAD_WAKEUP, &thread->flags);
> > + if (kthread_should_park())
> > + kthread_parkme();
> > if (!kthread_should_stop())
> > thread->run(thread);
> > }
> > diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
> > index 8cb79fc..5f817bd 100644
> > --- a/drivers/md/raid5-cache.c
> > +++ b/drivers/md/raid5-cache.c
> > @@ -19,6 +19,7 @@
> > #include <linux/raid/md_p.h>
> > #include <linux/crc32c.h>
> > #include <linux/random.h>
> > +#include <linux/kthread.h>
> > #include "md.h"
> > #include "raid5.h"
> > #include "bitmap.h"
> > @@ -1437,23 +1438,14 @@ void r5l_quiesce(struct r5l_log *log, int state)
> > struct mddev *mddev;
> > if (!log || state == 2)
> > return;
> > - if (state == 0) {
> > - /*
> > - * This is a special case for hotadd. In suspend, the array has
> > - * no journal. In resume, journal is initialized as well as the
> > - * reclaim thread.
> > - */
> > - if (log->reclaim_thread)
> > - return;
> > - log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
> > - log->rdev->mddev, "reclaim");
> > - log->reclaim_thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;
> > - } else if (state == 1) {
> > + if (state == 0)
> > + kthread_unpark(log->reclaim_thread->tsk);
>
> The old code tested for log->reclaim_thread being NULL. This new
> version will just crash.
But the reclaim_thread couldn't be NULL if log != NULL. Am I missing anything?
> > + else if (state == 1) {
> > /* make sure r5l_write_super_and_discard_space exits */
> > mddev = log->rdev->mddev;
> > wake_up(&mddev->sb_wait);
> > + kthread_park(log->reclaim_thread->tsk);
>
> r5l_do_reclaim has a wait loop internally. I think you need that to
> abort when kthread_should_park(), else this will block indefinitely.
Sounds not harmful to me. The loop in r5l_do_reclaim will eventually end if all
data is reclaimed. Then the thread will be in the md_thread() loop. In that
loop, the thread will not sleep because the wait checks kthread_should_park().
Then the thread will get parked.
Thanks,
Shaohua
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