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Date: Wed, 19 Jun 2013 18:32:34 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: linux-kernel@vger.kernel.org, Jan Kratochvil <jan.kratochvil@redhat.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>
Subject: Re: [PATCH] ptrace: make PTRACE_DETACH work on non-stopped tracees.
Message-ID: <20130619163234.GA12029@redhat.com>
References: <1371654936-31742-1-git-send-email-dvlasenk@redhat.com>
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On 06/19, Denys Vlasenko wrote:
>
> This is a user-visible behavior change.
> Do we really have to introduce a separate
> PTRACE_NOT_STUPID_DETACH? I hope not.

Oh, I think yes.

> @@ -1062,7 +1060,8 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
>  	}
>
>  	ret = ptrace_check_attach(child, request == PTRACE_KILL ||
> -				  request == PTRACE_INTERRUPT);
> +				  request == PTRACE_INTERRUPT ||
> +				  request == PTRACE_DETACH);

There doesn't look right.

For example ptrace_disable(). See the comment set_task_blockstep().
And flush_ptrace_hw_breakpoint() can race with the exiting task.

And the setting of ->exit_code is racy too.

And this makes the ptrace_unfreeze_traced() logic more confusing...
but probably this is fine.

Oleg.