From: Arnd Bergmann <arnd@arndb.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Binoy Jayan <binoy.jayan@linaro.org>,
linux-rdma@vger.kernel.org,
Mustafa Ismail <mustafa.ismail@intel.com>,
Lijun Ou <oulijun@huawei.com>,
Nicholas Bellinger <nab@linux-iscsi.org>,
Leon Romanovsky <leonro@mellanox.com>,
target-devel@vger.kernel.org,
Tatyana E Nikolova <tatyana.e.nikolova@intel.com>,
Doug Ledford <dledford@redhat.com>,
Jenny Derzhavetz <jennyf@mellanox.com>,
Sagi Grimberg <sagi@grimberg.me>,
Sean Hefty <sean.hefty@intel.com>,
Faisal Latif <faisal.latif@intel.com>,
Hal Rosenstock <hal.rosenstock@gmail.com>,
linux-kernel@vger.kernel.org,
"Wei Hu(Xavier)" <xavier.huwei@huawei.com>,
Mark Brown <broonie@kernel.org>, Mark Bloch <markb@mellanox.com>,
Steve Wise <swise@opengridcomputing.com>,
Ira Weiny <ira.weiny@intel.com>
Subject: Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait
Date: Mon, 21 Nov 2016 17:52:27 +0100 [thread overview]
Message-ID: <4374986.OFD8bCgUa1@wuerfel> (raw)
In-Reply-To: <CA+55aFxGjaqduhRCyk0mVxEA7aqQ-omdG8SBreZ=x5cW2ovngQ@mail.gmail.com>
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
WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@arndb.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Binoy Jayan <binoy.jayan@linaro.org>,
linux-rdma@vger.kernel.org,
Mustafa Ismail <mustafa.ismail@intel.com>,
Lijun Ou <oulijun@huawei.com>,
Nicholas Bellinger <nab@linux-iscsi.org>,
Leon Romanovsky <leonro@mellanox.com>,
target-devel@vger.kernel.org,
Tatyana E Nikolova <tatyana.e.nikolova@intel.com>,
Doug Ledford <dledford@redhat.com>,
Jenny Derzhavetz <jennyf@mellanox.com>,
Sagi Grimberg <sagi@grimberg.me>,
Sean Hefty <sean.hefty@intel.com>,
Faisal Latif <faisal.latif@intel.com>,
Hal Rosenstock <hal.rosenstock@gmail.com>,
linux-kernel@vger.kernel.org,
"Wei Hu(Xavier)" <xavier.huwei@huawei.com>,
Mark Brown <broonie@kernel.org>, Mark Bloch <markb@mellanox.com>,
Steve Wise <swise@opengridcomputing.com>,
Ira Weiny <ira.weiny@intel.com>,
Bart Van Assche <bart.vanassche@sandisk.com>,
Matan Barak <matanb@mellanox.com>,
Sagi Grimberg <sagig@mellanox.com>
Subject: Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait
Date: Mon, 21 Nov 2016 17:52:27 +0100 [thread overview]
Message-ID: <4374986.OFD8bCgUa1@wuerfel> (raw)
In-Reply-To: <CA+55aFxGjaqduhRCyk0mVxEA7aqQ-omdG8SBreZ=x5cW2ovngQ@mail.gmail.com>
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
next prev parent reply other threads:[~2016-11-21 16:52 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-21 6:08 [PATCH v5 0/9] infiniband: Remove semaphores Binoy Jayan
2016-11-21 6:08 ` Binoy Jayan
2016-11-21 6:08 ` [PATCH v5 1/9] IB/core: iwpm_nlmsg_request: Replace semaphore with completion Binoy Jayan
2016-11-21 6:08 ` [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait Binoy Jayan
[not found] ` <CA+55aFxGjaqduhRCyk0mVxEA7aqQ-omdG8SBreZ=x5cW2ovngQ@mail.gmail.com>
2016-11-21 16:52 ` Arnd Bergmann [this message]
2016-11-21 16:52 ` Arnd Bergmann
2016-11-21 16:57 ` Christoph Hellwig
2016-11-21 16:57 ` Christoph Hellwig
2016-11-21 17:57 ` Linus Torvalds
2016-11-21 17:57 ` Linus Torvalds
2016-11-21 22:51 ` Arnd Bergmann
2016-11-21 22:51 ` Arnd Bergmann
[not found] ` <1479708496-9828-1-git-send-email-binoy.jayan-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2016-11-21 6:08 ` [PATCH v5 3/9] IB/hns: Replace semaphore poll_sem with mutex Binoy Jayan
2016-11-21 6:08 ` Binoy Jayan
2016-11-21 6:08 ` [PATCH v5 4/9] IB/mthca: " Binoy Jayan
2016-11-21 6:08 ` [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion Binoy Jayan
2016-11-21 7:36 ` Sagi Grimberg
2016-11-21 10:22 ` Arnd Bergmann
2016-11-21 10:22 ` Arnd Bergmann
2016-11-21 12:33 ` Sagi Grimberg
2016-11-21 12:33 ` Sagi Grimberg
2016-11-21 14:50 ` Arnd Bergmann
2016-11-21 14:50 ` Arnd Bergmann
2016-11-21 6:08 ` [PATCH v5 6/9] IB/hns: Replace counting semaphore event_sem with wait_event Binoy Jayan
2016-11-21 6:08 ` [PATCH v5 7/9] IB/mthca: " Binoy Jayan
2016-11-21 6:08 ` [PATCH v5 8/9] IB/mlx5: Add helper mlx5_ib_post_send_wait Binoy Jayan
2016-11-21 6:08 ` [PATCH v5 9/9] IB/mlx5: Replace semaphore umr_common:sem with wait_event Binoy Jayan
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