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From: Oleg Nesterov <oleg@tv-sign.ru>
To: Andrew Morton <akpm@osdl.org>
Cc: ebiederm@xmission.com, torvalds@osdl.org,
	linux-kernel@vger.kernel.org, janak@us.ibm.com,
	viro@ftp.linux.org.uk, hch@lst.de, mtk-manpages@gmx.net,
	ak@muc.de, paulus@samba.org
Subject: Re: [PATCH] unshare: Use rcu_assign_pointer when setting sighand
Date: Sat, 18 Mar 2006 16:12:33 +0300	[thread overview]
Message-ID: <441C0741.3BC25010@tv-sign.ru> (raw)
In-Reply-To: 20060317125607.78a5dbe4.akpm@osdl.org

Andrew Morton wrote:
> 
> Oleg Nesterov <oleg@tv-sign.ru> wrote:
> >
> > Isn't it better to just replace this code with
> > 'BUG_ON(new_sigh != NULL)' ?
> >
> > It is never executed, but totally broken, afaics.
> > task_lock() has nothing to do with ->sighand changing.
> >
> 
> /*
>  * Unsharing of sighand for tasks created with CLONE_SIGHAND is not
>  * supported yet
>  */
> static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)
> 
> It's all just a place-holder at present.
> 
> If we don't plan on ever supporting unshare(CLONE_SIGHAND) we should take
> that code out and make it return EINVAL.  Right now.
> 
> And because we don't presently support CLONE_SIGHAND we should return
> EINVAL if it's set.  Right now.
> 
> And we should change sys_unshare() to reject not-understood flags.  Right
> now.
> 
> If we don't do these things we'll silently break 2.6.16-back-compatibility
> of applications which are coded for future kernels.

unshare_sighand() is ok, it never populates *new_sighp, it just returns
errror code: 0 when ->sighand is not shared, EINVAL otherwise.

I argued about 'if (new_sigh)' code in sys_unshare() because it lies about
locking rules.

Btw, copy_process() forbids CLONE_SIGHAND without CLONE_VM (is there a
good reason for that?), but one can do unshare(CLONE_VM). This is odd.

Oleg.

  reply	other threads:[~2006-03-18 13:15 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-03-16 16:49 [PATCH] unshare: Cleanup up the sys_unshare interface before we are committed Eric W. Biederman
2006-03-16 17:31 ` [PATCH] unshare: Use rcu_assign_pointer when setting sighand Eric W. Biederman
2006-03-17  6:48   ` Paul E. McKenney
2006-03-17 17:44   ` Oleg Nesterov
2006-03-17 20:56     ` Andrew Morton
2006-03-18 13:12       ` Oleg Nesterov [this message]
2006-03-18 15:43         ` Janak Desai
2006-03-18 17:24           ` Oleg Nesterov
2006-03-18 17:41             ` [PATCH] for 2.6.16, disable unshare_vm() Oleg Nesterov
2006-03-18 18:10               ` Linus Torvalds
2006-03-18 18:29                 ` Ulrich Drepper
2006-03-18 18:48                 ` Janak Desai
2016-03-14 13:15             ` unshare(CLONE_VM) Re: [PATCH] unshare: Use rcu_assign_pointer when setting sighand Julian Smith
2016-03-14 18:35               ` Linus Torvalds
2006-03-18 13:13       ` [PATCH] implement unshare(CLONE_SIGHAND) for single-thread case Oleg Nesterov
2006-03-18 15:10       ` [PATCH] unshare: Error if passed unsupported flags Eric W. Biederman
2006-03-18 15:33         ` Janak Desai
2006-03-18 16:29       ` [PATCH] unshare: Use rcu_assign_pointer when setting sighand Janak Desai
2006-03-16 19:40 ` [PATCH] unshare: Cleanup up the sys_unshare interface before we are committed Michael Kerrisk
2006-03-16 20:33 ` Andrew Morton
2006-03-16 20:41   ` Linus Torvalds
2006-03-16 21:58     ` Eric W. Biederman
2006-03-16 22:19       ` Andrew Morton
2006-03-16 21:36   ` Janak Desai

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