Re: [bug report] dead lock (?) occur on ap325 board

[Paul Mundt <lethal@linux-sh.org>]

On Tue, Jan 27, 2009 at 05:26:46PM +0900, morimoto.kuninori@renesas.com wrote:
> 
> Dear Paul
> 
> > I haven't been able to reproduce this yet, but it would be helpful to
> > know precisely where your lock up occurs. If you aren't using JTAG, you
> > can try sending an NMI, or send a register and/or stacktrace request via
> > magic sysrq.
> 
> I think I found the reason.
> 
> in "__mutex_fastpath_unlock" (arch/sh/include/asm/mutex-llsc.h),
> currect operation is following.
> 
> -------------------
> 	__res |= !__ex_flag;
> 	if (unlikely(__res <= 0))
> -------------------
> 
> But, This operation is wrong for me.
> I think following is correct ?
> 
> -------------------
>      	if (unlikely(__res <= 0 || __ex_flag = 0))
> -------------------
> 
> above patch works well and dead lock never occur
> on my local environment.
> If my opinion is correct, I will send patch.
> 
Hmm, the !__ex_flag should have handled that case properly, but I wonder
if it is negated in the unlock case. Does switching to __res |= __ex_flag
and leaving the existing test as-is fix it?