linux-kernel - Re: [REGRESSION] ptrace broken from "cgroup: cgroup v2 freezer" (76f969e)

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Date:   Mon, 13 May 2019 18:38:14 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>
Cc:     linux-kernel@...r.kernel.org, tj@...nel.org, guro@...com,
        kernel-team@...com
Subject: Re: [REGRESSION] ptrace broken from "cgroup: cgroup v2 freezer"
 (76f969e)

On 05/13, Oleg Nesterov wrote:
>
> Probably we add leave_frozen(true) after freezable_schedule() for now, then
> think try to make something better...

And again, this is what I thought ptrace_stop() does, somehow I didn't notice
that the last version doesn't have leave_frozen() in ptrace_stop().

Perhaps we can do a bit better, change only tracehook_report_syscall_entry() and
PTRACE_EVENT_EXIT/SECCOMP paths to do leave_frozen() ?

At first glance other callers look fine in that they can do nothing "interesting"
befor get_signal(), but we need to re-check...

Oleg.

> But I am not sure I 100% understand whats going on in this case, could you
> try the patch below? (Just in case, of course it is wrong).
> 
> Oleg.
> 
> --- x/kernel/signal.c
> +++ x/kernel/signal.c
> @@ -149,8 +149,7 @@
>  {
>  	if ((t->jobctl & (JOBCTL_PENDING_MASK | JOBCTL_TRAP_FREEZE)) ||
>  	    PENDING(&t->pending, &t->blocked) ||
> -	    PENDING(&t->signal->shared_pending, &t->blocked) ||
> -	    cgroup_task_frozen(t)) {
> +	    PENDING(&t->signal->shared_pending, &t->blocked) {
>  		set_tsk_thread_flag(t, TIF_SIGPENDING);
>  		return true;
>  	}
>