linux-kernel - Re: [PATCH 1/4] export kernel call get_task

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Message-ID: <alpine.DEB.2.00.1104201613270.13948@chino.kir.corp.google.com>
Date:	Wed, 20 Apr 2011 16:19:14 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Greg KH <gregkh@...e.de>,
	J Freyensee <james_p_freyensee@...ux.intel.com>,
	linux-kernel@...r.kernel.org, suhail.ahmed@...el.com,
	christophe.guerard@...el.com
Subject: Re: [PATCH 1/4] export kernel call get_task_comm().

On Wed, 20 Apr 2011, Andrew Morton wrote:

> > > But as David pointed out, if there is work other than mine coming that
> > > has already been proposed, wouldn't it be good to get this patch in
> > > place now to start the encouragement of future eyes to just call this
> > > function than re-invent the wheel?
> > 
> > No, then those projects submit the patch to export this, if they happen
> > to get to mainline before this one does.
> > 
> > Again, don't export something unless you are using it at the time, no
> > "this is to be used hopefully by something in the future" type stuff
> > please.  Who knows if those future plans ever pan out.
> 
> Well there's an easy solution here.  Send the patch to export
> get_task_comm(), then send along some patches which fix
> 
> z:/usr/src/linux-2.6.39-rc4> grep -r 'current->comm' drivers | wc -l
> 89
> 

If we go this route and continue to support /proc/pid/comm, then we're 
going to need to ensure nothing that dereferences p->comm for any thread p 
is in a blockable context and that it's acceptable for get_task_comm(p) to 
take task_lock(p), and that requires not nesting it with 
write_lock(&tasklist_lock).

I'm thinking that we're going to want to choose something else other than 
p->alloc_lock to protect p->comm since that lock is protecting so many 
different members of struct task_struct that we may not know whether it's 
held when we want to print p->comm.
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