This is the mail archive of the
gdb@sourceware.org
mailing list for the GDB project.
Re: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is traced
- From: Oleg Nesterov <oleg at redhat dot com>
- To: Pedro Alves <palves at redhat dot com>
- Cc: Denys Vlasenko <vda dot linux at googlemail dot com>, Denys Vlasenko <dvlasenk at redhat dot com>, Andrew Morton <akpm at linux-foundation dot org>, Dmitry Vyukov <dvyukov at google dot com>, Alexander Potapenko <glider at google dot com>, Eric Dumazet <edumazet at google dot com>, Jan Kratochvil <jan dot kratochvil at redhat dot com>, Julien Tinnes <jln at google dot com>, Kees Cook <keescook at google dot com>, Kostya Serebryany <kcc at google dot com>, Linus Torvalds <torvalds at linux-foundation dot org>, "Michael Kerrisk (man-pages)" <mtk dot manpages at gmail dot com>, Robert Swiecki <swiecki at google dot com>, Roland McGrath <roland at hack dot frob dot com>, syzkaller at googlegroups dot com, Linux Kernel Mailing List <linux-kernel at vger dot kernel dot org>, "gdb at sourceware dot org" <gdb at sourceware dot org>
- Date: Wed, 28 Oct 2015 20:02:35 +0100
- Subject: Re: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is traced
- Authentication-results: sourceware.org; auth=none
- References: <20151020171754 dot GA29304 at redhat dot com> <20151020153155 dot e03f4219da4014efe6f810b0 at linux-foundation dot org> <5627EE9E dot 8040600 at redhat dot com> <5627F607 dot 4050506 at redhat dot com> <20151021214703 dot GA1810 at redhat dot com> <CAK1hOcP027FAWg5uVDjiFDC+0=dGu5JFJcy9Jij4dY8SBnT4MA at mail dot gmail dot com> <20151025155440 dot GB2043 at redhat dot com> <562E17D8 dot 4000108 at redhat dot com> <20151028161152 dot GA24042 at redhat dot com> <5630ED16 dot 50900 at redhat dot com>
On 10/28, Pedro Alves wrote:
>
> On 10/28/2015 04:11 PM, Oleg Nesterov wrote:
> > On 10/26, Pedro Alves wrote:
> >>
> >> (Also, in the original test case, if the child gets/raises a signal or execs
> >> before exiting, the bash/init/whatever process won't be issuing PTRACE_CONT,
> >> and the child will thus end up stuck (though should be SIGKILLable,
> >
> > Oh, but if it is killable everything is fine. How does this differ from the
> > case when, say, you jusr reparent to init and do kill(getpid(), SIGSTOP) ?
>
> The difference is that if the child called PTRACE_TRACEME, then it goes
> to ptrace-stop instead and no amount of SIGCONT unstucks it -- the only way
> out is force killing. I agree it's not a major issue as there's a way out
> (and thus made it a parens), but I wouldn't call it nice either.
IOW, the difference is that it is TASK_TRACED, not TASK_STOPPED. I agree,
this is not nice. But this is not nice simply because PTRACE_TRACEME is
not nice.
> >> All this because PTRACE_TRACEME is broken by design
> >
> > Heh. I agree. But we can't fix it now.
>
> Perhaps the man page could document it as deprecated, suggesting
> PTRACE_ATTACH/PTRACE_SEIZE instead?
I don't know. but I won't mind if you mark PTRACE_ATTACH as deprecated
too ;) PTRACE_SEIZE can be used instead and it doesn't abuse SIGSTOP.
Oleg.