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Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within up()

From Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within up()
Date 2016-02-03 08:50 +0100
Message-ID <qY0mn-7ok-35@gated-at.bofh.it> (permalink)
References <qXYNz-6z9-15@gated-at.bofh.it> <qY030-7gg-19@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On (02/03/16 08:28), Ingo Molnar wrote:
[..]
> So why not move printk away from semaphores? Semaphores are classical constructs 
> that have legacies and are somewhat non-obvious to use, compared to modern, 
> simpler locking primitives. I'd not touch their implementation, unless we are 
> absolutely sure this is a safe optimization.

semaphore's spin_lock is not the only spin lock that printk acquires. it also takes the
logbuf_lock (and different locks in console drivers (up to console driver)).

Jan Kara posted a patch that offloads printing job (console_trylock()-console_unlock())
from printk() call (when printk can offload it). so semaphore and console driver's locks
will go away (mostly) with Jan's patch. logbug spin_lock, however, will stay.

	-ss

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Thread

[PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within up() Byungchul Park <byungchul.park@lge.com> - 2016-02-03 07:10 +0100
  Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within  up() Ingo Molnar <mingo@kernel.org> - 2016-02-03 08:30 +0100
    Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within  up() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-02-03 08:50 +0100
      Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within  up() Ingo Molnar <mingo@kernel.org> - 2016-02-03 09:10 +0100
        Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within  up() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-02-03 09:30 +0100
          Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within  up() Ingo Molnar <mingo@kernel.org> - 2016-02-03 10:10 +0100
      Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within  up() Byungchul Park <byungchul.park@lge.com> - 2016-02-03 09:20 +0100
        Re: [PATCH v2] lock/semaphore: Avoid an unnecessary deadlock within  up() Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2016-02-03 09:30 +0100

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