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Re: [patch] drivers/zram: Don't disable preemption in zcomp_stream_get/put()

From Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Newsgroups linux.kernel
Subject Re: [patch] drivers/zram: Don't disable preemption in zcomp_stream_get/put()
Date 2016-10-17 16:30 +0200
Message-ID <sth5n-4CT-1@gated-at.bofh.it> (permalink)
References <spcH2-6dt-141@gated-at.bofh.it> <ssK9r-62-1@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On 2016-10-16 05:14:22 [+0200], Mike Galbraith wrote:
> 
> In v4.7, the driver switched to percpu compression streams, disabling
> preemption (get/put_cpu_ptr()).  Use get/put_cpu_light() instead.

I am not convinced that this will work. Nothing prevents
zram_bvec_write() to be reentrant on the same CPU what I can tell from
browsing over the code and since it uses zstrm->buffer for compression
it can go wrong. Also I don't know if crypto's tfm handler can be used
in parallel for any ops (it usually does not work for crypto).

I suggest a local lock or a good reason why the this patch works.

Sebastian

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[patch] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-10-16 05:20 +0200
  Re: [patch] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-10-17 16:30 +0200
    Re: [patch] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-10-17 18:20 +0200
      Re: [patch] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-10-17 18:30 +0200
        Re: [patch] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-10-17 19:20 +0200
          Re: [patch] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-10-17 19:50 +0200
    [patch v2] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-10-19 18:00 +0200
      Re: [patch v2] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-10-19 19:00 +0200
        Re: [patch v2] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-10-20 05:00 +0200
      Re: [patch v2] drivers/zram: Don't disable preemption in  zcomp_stream_get/put() Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2016-10-20 13:10 +0200

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