linux-kernel - Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE

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Message-ID: <20110214090356.GA21979@host1.dyn.jankratochvil.net>
Date:	Mon, 14 Feb 2011 10:03:56 +0100
From:	Jan Kratochvil <jan.kratochvil@...hat.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
 PTRACE_ATTACH

On Mon, 14 Feb 2011 00:01:47 +0100, Denys Vlasenko wrote:
> * sleep runs in nanosleep
> * SIGSTOP arrives, strace sees it
> * strace logs it and allows it via ptrace(PTRACE_SYSCALL, ..., SIGSTOP)
> * sleep process enters group-stop

The last point breaks the documented behavior of ptrace:
	If data is nonzero and not SIGSTOP, it is interpreted as a signal to
	be delivered to the child; otherwise, no signal is delivered.

I do not see it would affect gdb.  strace will change its behavior when
SIGSTOP is sent to its tracee although the new behavior may be OK.

It is more a subject of apps compatibility testing with such a kernel change.


> * nothing happens until some other signal arrives
> * say, SIGCONT arrives

What if other signal arrives?  The tracer probably should not be notified as
the tracee is in a group-stop.


> * strace logs it and allows it via ptrace(PTRACE_SYSCALL, ..., SIGCONT)


Thanks,
Jan
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