From: Oleg Nesterov <oleg@redhat.com>
To: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Tejun Heo <tj@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
indan@nul.nu, bdonlan@gmail.com, linux-kernel@vger.kernel.org,
jan.kratochvil@redhat.com, akpm@linux-foundation.org
Subject: Re: thread leader death under strace (was Re: [PATCH 03/10] ptrace: implement PTRACE_SEIZE)
Date: Sat, 4 Jun 2011 17:27:26 +0200 [thread overview]
Message-ID: <20110604152726.GA5734@redhat.com> (raw)
In-Reply-To: <201106032010.03947.vda.linux@googlemail.com>
On 06/03, Denys Vlasenko wrote:
>
> On Friday 03 June 2011 17:29, Oleg Nesterov wrote:
> > > > > > thread_leader(void *unused)
> > > > > > {
> > > > > > /* malloc gives sufficiently aligned buffer.
> > > > > > * long buf[] does not! (on ia64).
> > > > > > */
> > > > > > clone2(thread1, malloc(16 * 1024), 16 * 1024, 0
> > > > >
> > > > > Probably because of this clone2.
> > >
> > > This seems to be not a problem (it is defined to clone()).
> >
> > Doesn't matter.
> >
> > Unlike pthread_create() which uses CLONE_SETTLS, this doesn't setup
> > the tls area, and I assume you used -lpthread. In this case it is clear
> > why raise() doesn't work, pt-raise.c thinks that THREAD_GETMEM(tid)
> > should always work.
>
> I don't link against pthread.
Hmm. OK, I was wrong, I thought that the !pt version in raise.c should
work because it does
selftid = THREAD_GETMEM(tid);
if (!selftid) {
selftid = sys_gettid();
THREAD_GETMEM(tid) = selftid;
}
and thus uses the correct tid. But it doesn't work because it uses the
wrong _pid_ by the same reason (tls). It rechecks THREAD_GETMEM(tid)
but not THREAD_GETMEM(pid), then it does
if (!pid)
pid = selftid;
and tgkill() correctly fails again.
Heh,
int tfunc(void *unused)
{
raise(SIGKILL);
printf("WTF? SIGKILL doesn't work\n");
printf("thread: tgid = %d\n", getpid());
exit(0);
}
char stack[32 * 1024];
int main(void)
{
printf("main: tgid = %ld\n", syscall(__NR_getpid));
clone(tfunc, stack + sizeof(stack)/2,
CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_THREAD,
NULL);
pause();
assert(0);
return 0;
}
prints
main: tgid = 5959
WTF? SIGKILL doesn't work
thread: tgid = 5960
on my machine. Note that if the main thread uses getpid() (which caches
the returned value in THREAD_GETMEM) instead of syscall, everything works.
And if you remove raise() from tfunc(), the thread prints the correct tgid.
This is because raise() fills THREAD_GETMEM(tid) which is used (why???) by
really_getpid() before sys_getpid().
Funny that...
On your machine you can have the different results, my glibc is rather
old. Anyway, I think we can conclude that there is no kernel bug involved.
I am not brave enough to contact glibc developers, may be you can ;)
Oleg.
prev parent reply other threads:[~2011-06-04 15:29 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-02 15:33 thread leader death under strace (was Re: [PATCH 03/10] ptrace: implement PTRACE_SEIZE) Denys Vlasenko
2011-06-02 16:36 ` Oleg Nesterov
2011-06-02 16:39 ` Oleg Nesterov
2011-06-02 22:26 ` Denys Vlasenko
2011-06-03 15:29 ` Oleg Nesterov
2011-06-03 18:10 ` Denys Vlasenko
2011-06-04 15:27 ` Oleg Nesterov [this message]
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