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Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep() hack

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On Sat, 5 Sep 2015 12:30:59 +0200 (CEST)
Thomas Gleixner <tglx@linutronix.de> wrote:

> So the problem we need to solve is:
> 
> retry:
> 	lock(B);
> 	if (!try_lock(A)) {
> 		unlock(B);
> 		cpu_relax();
> 		goto retry;
> 	}
> 
> So instead of doing that proposed magic boost, we can do something
> more straight forward:
> 
> retry:
> 	lock(B);
> 	if (!try_lock(A)) {
> 		lock_and_drop(A, B);
> 		unlock(A);
> 		goto retry;
> 	}
> 
> lock_and_drop() queues the task as a waiter on A, drops B and then
> does the PI adjustment on A. 

That was my original solution, and I believe I added patches to do
exactly that to the networking code in the past. I remember writing
that helper function such that on non PREEMPT_RT it was a nop.

I even had that solution in my slides at LinuxCon/LinuxPlumbers ;-)


But then I talk about dcache.c. Take a look at that file, and the
complexity of that. Is it safe to take the inode and dcache parent
locks after you unlock the other locks?

-- Steve
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[RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep() hack Steven Rostedt <rostedt@goodmis.org> - 2015-09-04 03:30 +0200
  [RFC][PATCH RT 3/3] rt: Make cpu_chill() into yield() and add new cpu_rest() as msleep(1) Steven Rostedt <rostedt@goodmis.org> - 2015-09-04 03:30 +0200
  [RFC][PATCH RT 2/3] locking: Convert trylock spinners over to spin_try_or_boost_lock() Steven Rostedt <rostedt@goodmis.org> - 2015-09-04 03:30 +0200
  [RFC][PATCH RT 1/3] locking: Add spin_try_or_boost_lock() infrastructure Steven Rostedt <rostedt@goodmis.org> - 2015-09-04 03:30 +0200
    Re: [RFC][PATCH RT 1/3] locking: Add spin_try_or_boost_lock()  infrastructure Steven Rostedt <rostedt@goodmis.org> - 2015-09-04 03:50 +0200
  Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Thomas Gleixner <tglx@linutronix.de> - 2015-09-05 12:40 +0200
    Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Ingo Molnar <mingo@kernel.org> - 2015-09-05 14:10 +0200
      Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Steven Rostedt <rostedt@goodmis.org> - 2015-09-05 14:30 +0200
      Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Thomas Gleixner <tglx@linutronix.de> - 2015-09-07 10:40 +0200
        Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Thomas Gleixner <tglx@linutronix.de> - 2015-09-07 12:20 +0200
        Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Ingo Molnar <mingo@kernel.org> - 2015-09-08 09:40 +0200
          Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Thomas Gleixner <tglx@linutronix.de> - 2015-09-08 10:20 +0200
            Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Ingo Molnar <mingo@kernel.org> - 2015-09-14 12:00 +0200
        Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Steven Rostedt <rostedt@goodmis.org> - 2015-09-08 19:00 +0200
          Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Steven Rostedt <rostedt@goodmis.org> - 2015-09-08 21:40 +0200
    Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Steven Rostedt <rostedt@goodmis.org> - 2015-09-05 14:20 +0200
      Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Steven Rostedt <rostedt@goodmis.org> - 2015-09-05 14:30 +0200
      Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Steven Rostedt <rostedt@goodmis.org> - 2015-09-05 15:00 +0200
        Re: [RFC][PATCH RT 0/3] RT: Fix trylock deadlock without msleep()  hack Thomas Gleixner <tglx@linutronix.de> - 2015-09-07 11:20 +0200

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