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Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait

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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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[PATCH v5 0/9] infiniband: Remove semaphores Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:10 +0100
  [PATCH v5 7/9] IB/mthca: Replace counting semaphore event_sem with wait_event Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:10 +0100
  [PATCH v5 6/9] IB/hns: Replace counting semaphore event_sem with wait_event Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:10 +0100
  [PATCH v5 3/9] IB/hns: Replace semaphore poll_sem with mutex Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:10 +0100
  [PATCH v5 8/9] IB/mlx5: Add helper mlx5_ib_post_send_wait Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:10 +0100
  [PATCH v5 1/9] IB/core: iwpm_nlmsg_request: Replace semaphore with completion Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:10 +0100
  [PATCH v5 9/9] IB/mlx5: Replace semaphore umr_common:sem with wait_event Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:20 +0100
  [PATCH v5 4/9] IB/mthca: Replace semaphore poll_sem with mutex Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:20 +0100
  [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:20 +0100
    Re: [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion Sagi Grimberg <sagi@grimberg.me> - 2016-11-21 08:40 +0100
      Re: [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion Arnd Bergmann <arnd@arndb.de> - 2016-11-21 11:30 +0100
        Re: [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion Sagi Grimberg <sagi@grimberg.me> - 2016-11-21 13:40 +0100
          Re: [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion Arnd Bergmann <arnd@arndb.de> - 2016-11-21 16:00 +0100
  [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait Binoy Jayan <binoy.jayan@linaro.org> - 2016-11-21 07:20 +0100
    Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic  wait Christoph Hellwig <hch@infradead.org> - 2016-11-21 18:00 +0100
    Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait Arnd Bergmann <arnd@arndb.de> - 2016-11-21 18:00 +0100
      Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait Linus Torvalds <torvalds@linux-foundation.org> - 2016-11-21 19:00 +0100
        Re: [PATCH v5 2/9] IB/core: Replace semaphore sm_sem with an atomic wait Arnd Bergmann <arnd@arndb.de> - 2016-11-22 00:00 +0100

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