linux-kernel - Re: [PATCH RFC] Make call_srcu() available during very early boot

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Message-Id: <20180814174443.GG24813@linux.vnet.ibm.com>
Date:   Tue, 14 Aug 2018 10:44:43 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     joel@...lfernandes.org, mathieu.desnoyers@...icios.com,
        peterz@...radead.org, tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] Make call_srcu() available during very early boot

On Tue, Aug 14, 2018 at 01:24:53PM -0400, Steven Rostedt wrote:
> On Tue, 14 Aug 2018 10:06:18 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> 
> > > >  #define __SRCU_STRUCT_INIT(name, pcpu_name)				\
> > > > -	{								\
> > > > -		.sda = &pcpu_name,					\
> > > > -		.lock = __SPIN_LOCK_UNLOCKED(name.lock),		\
> > > > -		.srcu_gp_seq_needed = 0 - 1,				\
> > > > -		__SRCU_DEP_MAP_INIT(name)				\
> > > > -	}
> > > > +{									\
> > > > +	.sda = &pcpu_name,						\
> > > > +	.lock = __SPIN_LOCK_UNLOCKED(name.lock),			\
> > > > +	.srcu_gp_seq_needed = 0 - 1,					\  
> > > 
> > > Interesting initialization of -1. This was there before, but still
> > > interesting none the less.  
> > 
> > If I recall correctly, this subterfuge suppresses compiler complaints
> > about initializing an unsigned long with a negative number.  :-/
> 
> Did you try:
> 
> 	.srcu_gp_seq_needed = -1UL,
> 
> ?

Works for my compiler, not sure what set of complaints pushed me in that
direction.

							Thanx, Paul