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Date: Mon, 18 Oct 2004 20:38:25 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Robert Love <rml@novell.com>
Cc: dwalker@mvista.com, linux-kernel@vger.kernel.org
Subject: Re: [patch] Voluntary Preempt additions
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* Robert Love <rml@novell.com> wrote:

> On Mon, 2004-10-18 at 10:49 -0700, Daniel Walker wrote:
>                                                                                    
> > - Modified latency tracer to trace non-preemptable mutex locking , in
> > /proc/lock_trace
> 
> Why?
> 
> It is a bug to have preemption disabled when entering non-atomic
> (schedulable) code, and a stack trace is dumped if that happens.
> 
> Isn't that sufficient?

also, i improved that stackdump in the U4/U5 patches (PREEMPT_TRACE) to
include a trace of critical sections held at that moment:

  [<c0169dcb>] sys_unlink+0xdc/0x129
  [<c01060b5>] sysenter_past_esp+0x52/0x71
 preempt count: 00000002
 . 2-level deep critical section nesting:
 .. entry 1: free_hot_cold_page+0x82/0x149 / (__pagevec_free+0x1f/0x28)
 .. entry 2: print_traces+0x1b/0x54 / (dump_stack+0x23/0x25)

While the stackdump indeed is supposed to clearly identify the critical
section, they can be quite large and opaque, sometimes they even lose
the information of where the lock was acquired, and in practice it's
much easier to use PREEMPT_TRACE.

	Ingo
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