linux-kernel - [Futex RFC] was Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic

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Date:	Thu, 28 May 2009 18:15:34 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	Pavel Machek <pavel@....cz>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Harald Welte <HaraldWelte@...tech.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: [Futex RFC] was Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic

On Thu May 28 2009, Michael S. Zick wrote:
> On Thu May 28 2009, Pavel Machek wrote:
> > Hi!
> > 
> > > > @hpa - I still like your suggestion that it is only one (or a few)
> > > > uses of atomic ops that is incorrect and in general atomic ops
> > > > should compile away on uni-processor.
> > > > 
> > > 
> > > Actually, the more I think about it the more I suspect there is a race
> > > condition either in the chip set or in any VIA-specific drivers (if
> > > there are any.)  Putting LOCKs in random places will slow the CPU down
> > > significantly, so it might resolve the race condition without actually
> > > solving the problem.
> > 
> > Which you can verify; replace lock with something slow (pushad,
> > popad)? And see what happens.
> > 
> > (And if it never ever triggers on hp2133, you have strong clue that it
> > may not be cpu-related, but bios-related or chipset related or something).
> > 
> > Some time ago I was trying to debug misterious hangs on some
> > via/fic machines. 
> > 
> > We never figured out what was wrong, but we discovered many other bios
> > bugs, and those were not being fixed; so debugging was
> > hard/impossible. Unfortunately I no longer have access to that hw.
> > 
> 
> Then I am not losing my mind here - *it is* a difficult problem.  ;)
> 
> > hp2133 did _not_ have that problem.
> >
> 
> Today's build has been playing me music for over 8 hours on the
> HP-2133 (C7M-CN896) but can't get past a couple of hours on the
> (fic) Everex Cloudbook (C7M-CX700).
> 
> Also, the distro on the Cloudbook is using pulse-audio - the
> distro on the HP is not.  So I am reviewing the recent bug
> fixes to kernel/futex for something over-looked.  ;)
> May be a wild goose chase, but I think pulse-audio uses futexes.
> 

Please, somebody apply an experienced eye-ball to this;
It does seem to make a difference, but tests have not run
for very long yet.

diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
index 1f11ce4..da3c801 100644
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -19,7 +19,8 @@
                     "\t.previous\n"                            \
                     _ASM_EXTABLE(1b, 3b)                       \
                     : "=r" (oldval), "=r" (ret), "+m" (*uaddr) \
-                    : "i" (-EFAULT), "0" (oparg), "1" (0))
+                    : "i" (-EFAULT), "0" (oparg), "1" (0)      \
+                    : "memory")

 #define __futex_atomic_op2(insn, ret, oldval, uaddr, oparg)    \
        asm volatile("1:\tmovl  %2, %0\n"                       \
@@ -35,7 +36,8 @@
                     _ASM_EXTABLE(2b, 4b)                       \
                     : "=&a" (oldval), "=&r" (ret),             \
                       "+m" (*uaddr), "=&r" (tem)               \
-                    : "r" (oparg), "i" (-EFAULT), "1" (0))
+                    : "r" (oparg), "i" (-EFAULT), "1" (0)      \
+                    : "memory")


Mike
> Thanks for the other hints.
> 
> Mike 
> > Try forcing maximum throttling, then move mouse for like five
> > seconds. If kbc dies, you have same buggy bios, and probably are
> > debugging same problem....
> > 								Pavel
> 
> 
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