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

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Date:	Mon, 16 May 2011 16:10:32 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, "Ted Ts'o" <tytso@....edu>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.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 Mon, 2011-05-16 at 23:54 +0200, Jiri Slaby wrote:
> On 05/16/2011 11:19 PM, John Stultz wrote:
> > Accessing task->comm requires proper locking. However in the past
> > access to current->comm could be done without locking. This
> > is no longer the case, so all comm access needs to be done
> > while holding the comm_lock.
> > 
> > In my attempt to clean up unprotected comm access, I've noticed
> > most comm access is done for printk output. To simplify correct
> > locking in these cases, I've introduced a new %ptc format,
> > which will print the corresponding task's comm.
> > 
> > Example use:
> > printk("%ptc: unaligned epc - sending SIGBUS.\n", current);
> > 
> > CC: Ted Ts'o <tytso@....edu>
> > CC: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > CC: David Rientjes <rientjes@...gle.com>
> > CC: Dave Hansen <dave@...ux.vnet.ibm.com>
> > CC: Andrew Morton <akpm@...ux-foundation.org>
> > CC: linux-mm@...ck.org
> > Signed-off-by: John Stultz <john.stultz@...aro.org>
> > ---
> >  lib/vsprintf.c |   24 ++++++++++++++++++++++++
> >  1 files changed, 24 insertions(+), 0 deletions(-)
> > 
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index bc0ac6b..b7a9953 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -797,6 +797,23 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
> >  	return string(buf, end, uuid, spec);
> >  }
> >  
> > +static noinline_for_stack
> 
> Actually, why noinline? Did your previous version have there some
> TASK_COMM_LEN buffer or anything on stack which is not there anymore?

No, I was just following how almost all of the pointer() called
functions were declared.

But with two pointers and a long, I add more then ip6_string() has on
the stack, which uses the same notation.

But I can drop that bit if there's really no need for it.

thanks
-john


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