linux-kernel - Re: [BUG on PREEMPT_RT, 2.6.23.1-rt5] in rt-mutex code and signals

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Date:	Sat, 17 Nov 2007 18:46:08 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Remy Bohmer <linux@...mer.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	RT <linux-rt-users@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [BUG on PREEMPT_RT, 2.6.23.1-rt5] in rt-mutex code and signals


* Daniel Walker <dwalker@...sta.com> wrote:

> > Actually, IMO, compat_semaphores behave like semaphores should 
> > behave, and thus the same as they behave on a non-RT kernel, and at 
> > the locations where the semaphores are now misused as mutexes on RT, 
> > we should replace them by differently-named-mutex-type-semaphores, 
> > or better: real-RT-mutexes..
> 
> The vast majority of semaphore are actually binary semaphores in the 
> Linux kernel .. So it's easier to mass convert semaphores to mutexes, 
> then address the ones that don't conform.. Usually they are converted 
> to the complete API in mainline..

right now there are 3992 mutex_lock() critical sections in the kernel 
and only 351 down() based critical sections are left.

fixing the top 20:

      4 &vuart_bus_priv.probe_mutex
      5 &connections_lock
      5 &irq_ptr->setting_up_sema
      5 &kbd->sem
      5 &pnp_res_mutex
      5 &port->port_lock
      5 &tq_init_sem
      6 &adb_handler_sem
      6 &dev->parent->sem
      6 &driver_lock
      6 &ha->vport_sem
      7 &big_buffer_sem
      8 &dir_f->sem
      9 &c->alloc_sem
     11 &dev->sem
     11 &usbvision->lock
     12 &c->erase_free_sem
     15 &u132->scheduler_lock
     16 &zfcp_data.config_sema
     17 &f->sem

would remove 164 of them, so it would convert half of the remaining 
semaphore use in the kernel. So the job is almost finished - would 
anyone like to go for the final grand feat: complete removal of 
semaphores from the kernel? :-)

	Ingo
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