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Re: [RFC 5/5] uprobes: add global breakpoints
- From: Sebastian Andrzej Siewior <bigeasy at linutronix dot de>
- To: Oleg Nesterov <oleg at redhat dot com>
- Cc: linux-kernel at vger dot kernel dot org, x86 at kernel dot org, Peter Zijlstra <a dot p dot zijlstra at chello dot nl>, Arnaldo Carvalho de Melo <acme at ghostprotocols dot net>, Roland McGrath <roland at redhat dot com>, Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>, Ananth N Mavinakaynahalli <ananth at in dot ibm dot com>, stan_shebs at mentor dot com, gdb-patches at sourceware dot org
- Date: Thu, 9 Aug 2012 19:18:02 +0200
- Subject: Re: [RFC 5/5] uprobes: add global breakpoints
- References: <1344355952-2382-1-git-send-email-bigeasy@linutronix.de> <1344355952-2382-6-git-send-email-bigeasy@linutronix.de> <20120808131457.GA5309@redhat.com>
* Oleg Nesterov | 2012-08-08 15:14:57 [+0200]:
>> What I miss right now is an interface to tell the user/gdb that there is a
>> program that hit a global breakpoint and is waiting for further instructions.
>> A "tail -f trace" does not work and may contain also a lot of other
>> informations. I've been thinking about a poll()able file which returns pids of
>> tasks which are put on hold. Other suggestions?
>
>Honestly, I am not sure this is that useful...
How would you notify gdb that there is a new task that hit a breakpoint?
Or learn yourself?
>OK, I'll try to read this patch later. But, at first glance,
Thank you.
>> @@ -286,8 +286,10 @@ static int ptrace_attach(struct task_struct *task, long request,
>> __ptrace_link(task, current);
>>
>> /* SEIZE doesn't trap tracee on attach */
>> - if (!seize)
>> + if (!seize) {
>> send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
>> + uprobe_wakeup_task(task, 1);
>> + }
>
>Can't understand why uprobe_wakeup_task() depends on !PTRACE_SEIZE
because in the SEIZE case the task isn't halted, it continues to run. Or
do you want to use PTRACE_SEIZE for tasks which hit the global
breakpoint and you have no interrest in them and want them to continue
like nothing happend?
>> +
>> + set_current_state(TASK_TRACED);
>> + schedule();
>> +}
>
>Suppose that uprobe_wakeup_task() is called in the WINDOW above.
>
>OTOH, uprobe_wakeup_task() can race with itself if it is called
>twice at the same time, say from uprobes_gp_wakeup_write() and
>ptrace_attach().
Okay, I'm going to close the window.
>
>Oleg.
Sebastian