linux-kernel - Re: [PATCH] lib/vsprintf: add %pT format specifier

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Date:	Sat, 11 Jan 2014 12:35:25 +0100
From:	Pavel Machek <pavel@....cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, joe@...ches.com,
	keescook@...omium.org, geert@...ux-m68k.org, jkosina@...e.cz,
	viro@...iv.linux.org.uk, davem@...emloft.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/vsprintf: add %pT format specifier

On Fri 2014-01-10 17:57:30, Andrew Morton wrote:
> On Sat, 11 Jan 2014 10:28:51 +0900 Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> wrote:
> 
> > Andrew Morton wrote:
> > > On Thu, 9 Jan 2014 21:52:00 +0900 Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> wrote:
> > > 
> > > > This patch introduces %pT format specifier for printing task_struct->comm.
> > > > Currently %pT does not provide consistency. I'm planning to change to use RCU
> > > > in the future. By using RCU, the comm name read from task_struct->comm will be
> > > > guaranteed to be consistent. But before modifying set_task_comm() to use RCU,
> > > > we need to kill direct ->comm users who do not use get_task_comm().
> > > 
> > > On reflection...
> > > 
> > > It isn't obvious that this patch is sufficiently beneficial until we
> > > have that RCU code in place.
> > > 
> > > So I could retain this patch in -mm until we have that all sorted out. 
> > > And I'll have to avoid merging %pT users into mainline in the
> > > meanwhile!
> > > 
> > > Am I wrong?  The patch seems fairly pointless as a standalone thing?
> > > 
> > 
> >   Step 1: (targeted to 3.14-rc1)
> >     Add "%pT" format specifier and commcpy() wrapper function.
> > 
> >   Step 2: (started after step 1 is reflected to other git trees)
> >     Replace printk("%s", p->comm) with printk("%pT", p).
> >     Replace strcpy(buf, p->comm) with commcpy(buf, p).
> > 
> >   Step 3: (started after step 2 is reflected to other git trees)
> >     Add rcu_read_lock()/rcu_read_unlock() into commcpy().
> >     Modify set_task_comm() etc. to replace ->comm using RCU.
> 
> In the absence of step 3, steps 1 and 2 are rather pointless churn.

Dunno. Given how often it appears in the code, it looks to me like
step 1 is worthwile cleanup on its own...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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