linux-kernel - Re: [PATCH v5 3.1.0-rc4-tip 26/26] uprobes: queue signals while thread is singlestepping.

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Date:	Tue, 27 Sep 2011 15:03:46 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jonathan Corbet <corbet@....net>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 26/26]   uprobes: queue signals while
 thread is singlestepping.

On Tue, 2011-09-20 at 17:35 +0530, Srikar Dronamraju wrote:
> +#ifdef CONFIG_UPROBES
> +       if (!group && t->utask && t->utask->active_uprobe)
> +               pending = &t->utask->delayed;
> +#endif
> +
>         /*
>          * Short-circuit ignored signals and support queuing
>          * exactly one non-rt signal, so that we can get more
> @@ -1106,6 +1111,11 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
>                 }
>         }
>  
> +#ifdef CONFIG_UPROBES
> +       if (!group && t->utask && t->utask->active_uprobe)
> +               return 0;
> +#endif
> +
>  out_set:
>         signalfd_notify(t, sig);
>         sigaddset(&pending->signal, sig);
> @@ -1569,6 +1579,13 @@ int send_sigqueue(struct sigqueue *q, struct task_struct *t, int group)
>         }
>         q->info.si_overrun = 0;
>  
> +#ifdef CONFIG_UPROBES
> +       if (!group && t->utask && t->utask->active_uprobe) {
> +               pending = &t->utask->delayed;
> +               list_add_tail(&q->list, &pending->list);
> +               goto out;
> +       }
> +#endif
>         signalfd_notify(t, sig);
>         pending = group ? &t->signal->shared_pending : &t->pending;
>         list_add_tail(&q->list, &pending->list);
> @@ -2199,7 +2216,10 @@ int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
>                         spin_unlock_irq(&sighand->siglock);
>                         goto relock;
>                 }
> -
> +#ifdef CONFIG_UPROBES
> +               if (current->utask && current->utask->active_uprobe)
> +                       break;
> +#endif 

That's just crying for something like:

#ifdef CONFIG_UPROBES
static inline bool uprobe_delay_signal(struct task_struct *p)
{
	return p->utask && p->utask->active_uprobe;
}
#else
static inline bool uprobe_delay_signal(struct task_struct *p)
{
	return false;
}
#endif

That'll instantly kill the #ifdeffery as well as describe wtf you're
actually doing.
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