linux-kernel - Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm

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Date:	Thu, 12 May 2011 15:10:13 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	John Stultz <john.stultz@...aro.org>
cc:	Joe Perches <joe@...ches.com>, LKML <linux-kernel@...r.kernel.org>,
	"Ted Ts'o" <tytso@....edu>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [PATCH 2/3] printk: Add %ptc to safely print a task's comm

On Tue, 10 May 2011, John Stultz wrote:

> > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > > index bc0ac6b..b9c97b8 100644
> > > --- a/lib/vsprintf.c
> > > +++ b/lib/vsprintf.c
> > > @@ -797,6 +797,26 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
> > >  	return string(buf, end, uuid, spec);
> > >  }
> > >  
> > > +static noinline_for_stack
> > > +char *task_comm_string(char *buf, char *end, u8 *addr,
> > > +			 struct printf_spec spec, const char *fmt)
> > 
> > addr should be void * not u8 *
> > 
> > > +{
> > > +	struct task_struct *tsk = (struct task_struct *) addr;
> > 
> > no cast.
> > 
> > Maybe it'd be better to use current inside this routine and not
> > pass the pointer at all.
> 
> That sounds reasonable. Most users are current, so forcing the more rare
> non-current users to copy it to a buffer first and use the normal %s
> would not be of much impact.
> 

Please still require an argument, otherwise the oom killer (which could 
potentially called right before a stack overflow) would be required to use 
buffers for the commands printed in the tasklist dump.

> Although I'm not sure if there's precedent for a %p value that didn't
> take a argument. Thoughts on that? Anyone else have an opinion here?
> 

After the cleanups are addressed:

	Acked-by: David Rientjes <rientjes@...gle.com>

It would have been nice if we could force %ptc to expect a 
struct task_struct * rather than a void *, however.
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