linux-kernel - Re: [PATCH 2/2] Add new PTRACE_O_TRACESTOP option, make it control new ptrace behavior.

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Date:	Tue, 6 Sep 2011 22:08:18 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] Add new PTRACE_O_TRACESTOP option, make it control
	new ptrace behavior.

On 09/05, Denys Vlasenko wrote:
>
> Add new PTRACE_O_TRACESTOP option, make it control new ptrace behavior.
>
> Introduce new ptrace option, PTRACE_O_TRACESTOP. This makes API
> more symmetric: every PTRACE_EVENT_event has corresponding PTRACE_O_TRACEevent now,
> as it used to have before PTRACE_SEIZE was introduced.
>
> PTRACE_SEIZE does not assume PTRACE_O_TRACESTOP, but with this patch
> it allows any PTRACE_O_opts to be set at attach time

Well. This assumes that the only difference with PTRACE_SEIZE is the
new stop/interrupt behaviour. I am not sure this is "safe" to assume.

Tejun, what do you think?

>From the correctness pov, the patch is mostly correct. but you forgot
to update ptrace_init_task(). I bet you didn't try to test the patch ;)

>  int ptrace_request(struct task_struct *child, long request,
>  		   unsigned long addr, unsigned long data)
>  {
> -	bool seized = child->ptrace & PT_SEIZED;
> +	bool stop_events_enabled = child->ptrace & PT_TRACE_STOP;

May be ptrace_event_enabled(child, PTRACE_EVENT_STOP) looks better...
The same about other PT_TRACE_STOP checks, although this is cosmetic.


And. Given that you can set/clear PT_TRACE_STOP in ptrace_setoptions(),
you need the locking.

Just for example. do_signal_stop() calls ptrace_trap_notify() and hits
WARN_ON_ONCE(!PT_TRACE_STOP) because it was cleared in between.

Oleg.

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