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Message-ID: <4374986.OFD8bCgUa1@wuerfel>
Date: Mon, 21 Nov 2016 17:52:27 +0100
From: Arnd Bergmann <arnd@...db.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Binoy Jayan <binoy.jayan@...aro.org>, linux-rdma@...r.kernel.org,
Mustafa Ismail <mustafa.ismail@...el.com>,
Lijun Ou <oulijun@...wei.com>,
Nicholas Bellinger <nab@...ux-iscsi.org>,
Leon Romanovsky <leonro@...lanox.com>,
target-devel@...r.kernel.org,
Tatyana E Nikolova <tatyana.e.nikolova@...el.com>,
Doug Ledford <dledford@...hat.com>,
Jenny Derzhavetz <jennyf@...lanox.com>,
Sagi Grimberg <sagi@...mberg.me>,
Sean Hefty <sean.hefty@...el.com>,
Faisal Latif <faisal.latif@...el.com>,
Hal Rosenstock <hal.rosenstock@...il.com>,
linux-kernel@...r.kernel.org,
"Wei Hu(Xavier)" <xavier.huwei@...wei.com>,
Mark Brown <broonie@...nel.org>,
Mark Bloch <markb@...lanox.com>,
Steve Wise <swise@...ngridcomputing.com>,
Ira Weiny <ira.weiny@...el.com>,
Bart Van Assche <bart.vanassche@...disk.com>,
Matan Barak <matanb@...lanox.com>,
Sagi Grimberg <sagig@...lanox.com>
Subject: Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait
On Monday, November 21, 2016 7:57:53 AM CET Linus Torvalds wrote:
> Don't do this.
>
> Never ever do your own locking primitives. You will get the memory ordering
> wrong. And even if you get it right, why do it?
>
> If you want to get rid of semaphores, and replace them with a mutex, that's
> OK. But don't replace them with something more complex like an open coded
> waiting model.
I think a mutex would't work here, since fops->open() and fops->close()
are not called from the same context and lockdep will complain
about that.
Version of the series had replaced the semaphore with a completion
here, which worked correctly, but one reviewer suggested using
the wait_event() instead since it's confusing to have a completion
starting out in 'completed' state.
Arnd
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