linux-kernel - Re: [PATCH 08/14] ptrace: make do_signal_stop() use ptrace

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Message-ID: <20101128195442.GB12896@redhat.com>
Date:	Sun, 28 Nov 2010 20:54:42 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	roland@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	"rjw@...k.plpavel"@ucw.cz,
	Jan Kratochvil <jan.kratochvil@...hat.com>
Subject: Re: [PATCH 08/14] ptrace: make do_signal_stop() use ptrace_stop()
	if the task is being ptraced

On 11/26, Tejun Heo wrote:
>
> A ptraced task would still stop at do_signal_stop() when it's stopping
> for stop signals and do_signal_stop() behaves the same whether the
> task is ptraced or not.  However, in addition to stopping,
> ptrace_stop() also does ptrace specific stuff like calling
> architecture specific callbacks, so this behavior makes the code more
> fragile and difficult to understand.

OK. This patch adds the obviously user-visible change. It looks
very minor, but I never know when it comes to ptrace.

To simplify, suppose that we have a single-thread tracee, and
debugger "acks" SIGSTOP, say, it does ptrace(PTRACE_CONT, SIGSTOP).

Before this patch, the tracee stops in TASK_STOPPED, now it calls
ptrace_stop() and goes to TASK_TRACED state.

Add Jan. I hope this is OK, but this might break the tracer if
it looks into fs/proc (probably only test-cases do this).

At least, with or without this patch ->last_siginfo is NULL, good.

The check in do_signal_stop() looks racy though, see the next
email.

Oleg.

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