Re: [PATCH] test_rhashtable: remove semaphore usage
From: Phil Sutter
Date: Tue Dec 11 2018 - 02:38:49 EST
On Tue, Dec 11, 2018 at 01:45:52PM +0800, Herbert Xu wrote:
> On Mon, Dec 10, 2018 at 10:17:20PM +0100, Arnd Bergmann wrote:
> > This is one of only two files that initialize a semaphore to a negative
> > value. We don't really need the two semaphores here at all, but can do
> > the same thing in more conventional and more effient way, by using a
> > single waitqueue and an atomic thread counter.
> > This gets us a little bit closer to eliminating classic semaphores from
> > the kernel. It also fixes a corner case where we fail to continue after
> > one of the threads fails to start up.
> > An alternative would be to use a split kthread_create()+wake_up_process()
> > and completely eliminate the separate synchronization.
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> > This is part of a longer, untested, series to remove semaphores
> > from the kernel, please review as such before applying.
> > ---
> > lib/test_rhashtable.c | 28 ++++++++++++++++------------
> > 1 file changed, 16 insertions(+), 12 deletions(-)
> This was created by Phil Sutter so I am adding him to the cc list.
Thanks, I would have missed it otherwise. Just a minor nit:
> > diff --git a/lib/test_rhashtable.c b/lib/test_rhashtable.c
> > index 18de5ff1255b..12bdea4f6c20 100644
> > --- a/lib/test_rhashtable.c
> > +++ b/lib/test_rhashtable.c
> > @@ -635,8 +636,9 @@ static int threadfunc(void *data)
> > int i, step, err = 0, insert_retries = 0;
> > struct thread_data *tdata = data;
> > - up(&prestart_sem);
> > - if (down_interruptible(&startup_sem))
> > + if (atomic_dec_and_test(&startup_count))
> > + wake_up(&startup_wait);
> > + if (wait_event_interruptible(startup_wait, atomic_read(&startup_count) == -1))
> > pr_err(" thread[%d]: down_interruptible failed\n", tdata->id);
The error message should probably be adjusted as well. Apart from that:
Acked-by: Phil Sutter <phil@xxxxxx>