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

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Message-ID: <20110226035900.GD1656@ucw.cz>
Date:	Sat, 26 Feb 2011 04:59:01 +0100
From:	Pavel Machek <pavel@....cz>
To:	Jan Kratochvil <jan.kratochvil@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	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 2011-02-14 10:03:56, Jan Kratochvil wrote:
> 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.

apps compatibility testing?

No, we don't change kernel APIs like that -- those are called
regressions.

Just make ptrace(PTRACE_SYSCALL_2, ...) with fixed semantics.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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