linux-kernel - Re: [PATCH] signal: protect SIGNAL_UNKILLABLE from unintentional clearing.

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Message-ID: <20161128121434.4it7yd7wmpkxv6f4@cedar>
Date:   Mon, 28 Nov 2016 12:14:34 +0000
From:   Jamie Iles <jamie.iles@...cle.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Jamie Iles <jamie.iles@...cle.com>, linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] signal: protect SIGNAL_UNKILLABLE from unintentional
 clearing.

Hi Oleg,

On Thu, Nov 17, 2016 at 08:04:20PM +0100, Oleg Nesterov wrote:
> On 11/16, Jamie Iles wrote:
> >
> > This can result in init becoming stoppable/killable after tracing.  For
> > example, running:
> >
> >   while true; do kill -STOP 1; done &
> >   strace -p 1
> 
> > and then stopping strace and the kill loop will result in init being
> > left in state TASK_STOPPED.  Sending SIGCONT to init will resume it, but
> > init will now respond to future SIGSTOP signals rather than ignoring
> > them.
> 
> Yes, and a lot more... I forgot about these problems again.
> 
> Jamie, sorry for delay, I'll try to read the patch and reply tomorrow.

Did you get chance to look at the patch?  I did have another thought - 
rather than the accessors, we could change signal_struct to have:

  unsigned int unkillable:1;
  unsigned int flags:31;

to separate signal_unkillable from flags, making it a bit safer in the 
future.

Jamie