linux-kernel - Re: + signal-turn-dequeue_signal_lock-into-kernel_dequeue

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Message-ID: <20151024200918.GB16521@pengutronix.de>
Date:	Sat, 24 Oct 2015 22:09:18 +0200
From:	Markus Pargmann <mpa@...gutronix.de>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	akpm@...ux-foundation.org, balbi@...com, dwmw2@...radead.org,
	tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: +
 signal-turn-dequeue_signal_lock-into-kernel_dequeue_signal.patch added to
 -mm tree

Hi Oleg,

On Sat, Oct 24, 2015 at 09:48:26PM +0200, Oleg Nesterov wrote:
> Hi Markus,
> 
> s/mm-commits/lkml/
> 
> On 10/24, Markus Pargmann wrote:
> >
> > On Mon, Oct 05, 2015 at 02:19:27PM -0700, akpm@...ux-foundation.org wrote:
> > >
> > > Subject: signal: turn dequeue_signal_lock() into kernel_dequeue_signal()
> > >
> > > 1. Rename dequeue_signal_lock() to kernel_dequeue_signal(). This
> > >    matches another "for kthreads only" kernel_sigaction() helper.
> > >
> > > 2. Remove the "tsk" and "mask" arguments, they are always current
> > >    and current->blocked. And it is simply wrong if tsk != current.
> > >
> > > 3. We could also remove the 3rd "siginfo_t *info" arg but it looks
> > >    potentially useful. However we can simplify the callers if we
> > >    change kernel_dequeue_signal() to accept info => NULL.
> > >
> > > 4. Remove _irqsave, it is never called from atomic context.
> >
> > I just realised that this patch will conflict with a fixup patch for nbd
> > that will be included in rc7.
> >
> > dcc909d90ccd (nbd: Add locking for tasks)
> >
> > I think there is basically one new instance of dequeue_signal_lock() that
> > needs to be replaced with kernel_dequeue_signal().
> 
> Thanks! I'll send *-fix.patch to Andrew.
> 
> But you know, dcc909d90ccd (nbd: Add locking for tasks) doesn't look exactly
> right at first glance, although I need to re-check tomorrow...

In which regard? Is the locking incorrect or am I doing something wrong
with the signal handling?

> 
> One question, can sock_xmit() be called from user space? Or it is only called
> by kthreads?

sock_xmit() can be called by a thread that entered from userspace. In
general the idea is that there are no pending signals when it leaves
into userspace again.

Best Regards,

Markus

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