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Re: strace lockup when tracing exec in go

From Oleg Nesterov <oleg@redhat.com>
Newsgroups linux.kernel
Subject Re: strace lockup when tracing exec in go
Date 2016-09-23 12:30 +0200
Message-ID <skvTY-2pQ-41@gated-at.bofh.it> (permalink)
References (4 earlier) <sk8NI-4AG-35@gated-at.bofh.it> <sk8Xn-4DU-7@gated-at.bofh.it> <sk973-4Wz-1@gated-at.bofh.it> <ska38-5ym-33@gated-at.bofh.it> <skcHF-74T-39@gated-at.bofh.it>
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On 09/22, Michal Hocko wrote:
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -91,6 +91,10 @@ static int sig_ignored(struct task_struct *t, int sig, bool force)
>  	if (!sig_task_ignored(t, sig, force))
>  		return 0;
>  
> +	/* Do not ignore signals sent from child to the parent */
> +	if (current->ptrace && current->parent == t)
> +		return 0;

This doesn't look right in general, and this can't really help.

This assumes that the tracer will call do_wait() after mm_access()
fails, but this is not necessarily true.

Note also ptrace_attach(), -ERESTARTNOINTR means that the tracer won't
even return to user-space if SIGCHLD is ignored, the tracer will silently
restart the syscall.

Oleg.

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Thread

strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-21 17:40 +0200
  Re: strace lockup when tracing exec in go Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-09-22 06:20 +0200
    Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-22 10:10 +0200
      Re: strace lockup when tracing exec in go Aleksa Sarai <asarai@suse.com> - 2016-09-22 10:30 +0200
      Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-22 10:40 +0200
        Re: strace lockup when tracing exec in go Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-09-22 11:50 +0200
          Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-22 12:00 +0200
            Re: strace lockup when tracing exec in go Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-09-22 12:10 +0200
              Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-22 13:10 +0200
                Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-22 16:00 +0200
                Re: strace lockup when tracing exec in go Aleksa Sarai <asarai@suse.com> - 2016-09-23 03:20 +0200
                Re: strace lockup when tracing exec in go Oleg Nesterov <oleg@redhat.com> - 2016-09-23 12:30 +0200
                Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-23 13:20 +0200
                Re: strace lockup when tracing exec in go Oleg Nesterov <oleg@redhat.com> - 2016-09-23 15:30 +0200
                Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-23 15:50 +0200
                Re: strace lockup when tracing exec in go Oleg Nesterov <oleg@redhat.com> - 2016-09-23 16:10 +0200
                Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-23 16:20 +0200
  Re: strace lockup when tracing exec in go Oleg Nesterov <oleg@redhat.com> - 2016-09-23 12:00 +0200
    Re: strace lockup when tracing exec in go Michal Hocko <mhocko@kernel.org> - 2016-09-23 13:30 +0200

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