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Subject: Re: [PATCH v5 3.1.0-rc4-tip 26/26]   uprobes: queue signals while
 thread is singlestepping.
From: Peter Zijlstra <peterz@infradead.org>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
        Linux-mm <linux-mm@kvack.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Hugh Dickins <hughd@google.com>, Christoph Hellwig <hch@infradead.org>,
        Andi Kleen <andi@firstfloor.org>, Thomas Gleixner <tglx@linutronix.de>,
        Jonathan Corbet <corbet@lwn.net>, Oleg Nesterov <oleg@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jim Keniston <jkenisto@linux.vnet.ibm.com>,
        Roland McGrath <roland@hack.frob.com>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        LKML <linux-kernel@vger.kernel.org>
Date: Tue, 27 Sep 2011 15:03:46 +0200
In-Reply-To: <20110920120517.25326.57657.sendpatchset@srdronam.in.ibm.com>
References: <20110920115938.25326.93059.sendpatchset@srdronam.in.ibm.com>
	 <20110920120517.25326.57657.sendpatchset@srdronam.in.ibm.com>
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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.