linux-kernel - Re: [PATCH RT] add missing local serialization in ip

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Date:	Fri, 17 Jan 2014 20:40:58 +0100
From:	Nicholas Mc Guire <der.herr@...r.at>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-rt-users@...r.kernel.org,
	Sami Pietikainen <Sami.Pietikainen@...ice.com>,
	Jouko Haapaluoma <jouko.haapaluoma@...ice.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH RT] add missing local serialization in ip_output.c

On Fri, 17 Jan 2014, Steven Rostedt wrote:

> On Fri, 17 Jan 2014 16:33:23 +0100
> Nicholas Mc Guire <der.herr@...r.at> wrote:
> 
> > On Fri, 17 Jan 2014, Sebastian Andrzej Siewior wrote:
> > 
> > > On 01/17/2014 03:59 PM, Nicholas Mc Guire wrote:
> > > > On Fri, 17 Jan 2014, Sebastian Andrzej Siewior wrote:
> > > > 
> > > >> This is what I am going to apply. It also dropped the get_cpu_light()
> > > >> call which was added in a patch to remove the get_cpu_var() and is now
> > > >> no longer required since we have the get_locked_var() thingy now.
> > > >>
> > > > 
> > > > I do not think you can drop that - what is preventing migration now ?
> > > 
> > > Nothing but I do not see the need for it.
> > > 
> > > > 
> > > > #define get_locked_var(lvar, var)                                       \
> > > >         (*({                                                            \
> > > >                 local_lock(lvar);                                       \
> > > >                 &__get_cpu_var(var);                                    \
> > > >         }))
> > > > 
> > q> > No migrate_disable here - so how is this protected against migration ?
> 
> I was just about to reply to this, that local_lock() grabs a spinlock
> which does do a migrate disable. But you also noticed that the
> get_local_var() does a migrate disable too. We now have double the
> protection, so we are safe as Sebastion has done it.
>
...well that motivates a further migration cleanup patch replacing
the spin_*lock* by spin_*lock*_local variants to drop that recursive call
and while checking call paths - do a little API cleanup for softirq_lock

thx!
hofrat
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