From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phil Sutter Subject: Re: [PATCH] test_rhashtable: remove semaphore usage Date: Tue, 11 Dec 2018 08:38:25 +0100 Message-ID: <20181211073825.GT30790@orbyte.nwl.cc> References: <20181210211957.210189-1-arnd@arndb.de> <20181211054552.peone47xl5czpfar@gondor.apana.org.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Arnd Bergmann , Thomas Graf , "David S. Miller" , NeilBrown , Tom Herbert , Kees Cook , Paul Blakey , netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Herbert Xu Return-path: Content-Disposition: inline In-Reply-To: <20181211054552.peone47xl5czpfar@gondor.apana.org.au> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Hi, 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 > > --- > > 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 Thanks, Phil