linux-kernel - Re: [PATCH] pidns: limit the nesting depth of pid namespaces

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Message-Id: <20121024124607.43f599e8.akpm@linux-foundation.org>
Date:	Wed, 24 Oct 2012 12:46:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Wagin <avagin@...il.com>
Cc:	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] pidns: limit the nesting depth of pid namespaces

On Wed, 24 Oct 2012 09:38:57 +0400
Andrey Wagin <avagin@...il.com> wrote:

> >
> > I think that returning -ENOMEM in response to an excessive nesting
> > attempt is misleading - the system *didn't* run out of memory.  EINVAL
> > is better?
> 
> I chose ENOMEM by analogy with max_pid.  When a new PID can not be
> allocated, ENOMEM is returned too.

I don't know what this means - please be carefully specific when
identifying kernel code.

If you're referring to kernel/pid.c:alloc_pid() then -ENOMEM is
appropriate there, because a failure *is* caused by memory allocation
failure.

But ENOMEM isn't appropriate for nesting-depth-exceeded - we shouldn't
tell the user "you ran out of memory" when he didn't!  -EINVAL isn't
really appropriate either ("Invalid argument") but it has become a
general you-screwed-up catchall and seems to me to be the most
appropriate errno we have available.

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