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

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Message-Id: <201401111048.IFE82362.VOOSJHFFQMLtOF@I-love.SAKURA.ne.jp>
Date:	Sat, 11 Jan 2014 10:48:19 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	joe@...ches.com
Cc:	akpm@...ux-foundation.org, pavel@....cz, 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

Joe Perches wrote:
> On Sat, 2014-01-11 at 10:28 +0900, Tetsuo Handa wrote:
> >   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 printk("%s", current->comm) with printk("%pT", NULL);
> 
> ?

Right. I forgot to add it.

> 
> >     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.
> 
> Aren't steps 2 and 3 independent?
> 

If step 3 is merged before step 2 complete, those who are not using
"%pT" or commcpy() might crash due to reading RCU protected ->comm without
rcu_read_lock()/rcu_read_unlock(). 

Step 2 depends on step 1 for avoiding compile time errors.
Step 3 depends on step 2 for avoiding run time errors.
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