linux-kernel - Re: [PATCH 1/2] ptrace: make wait_on_bit(JOBCTL_TRAPPING_BIT) in ptrace

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Date:	Mon, 23 Nov 2015 18:05:52 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Pedro Alves <palves@...hat.com>,
	Jan Kratochvil <jan.kratochvil@...hat.com>
Subject: Re: [PATCH 1/2] ptrace: make wait_on_bit(JOBCTL_TRAPPING_BIT) in
 ptrace_attach() killable

On Thu, Nov 19, 2015 at 07:47:32PM +0100, Oleg Nesterov wrote:
> ptrace_attach() can hang waiting for STOPPED -> TRACED transition if the
> tracee gets frozen in between, change wait_on_bit() to use TASK_KILLABLE.
> 
> This doesn't really solve the problem(s) and we probably need to fix the
> freezer. In particular, note that this means that pm freezer will fail if
> it races attach-to-stopped-task.
> 
> And otoh perhaps we can just remove JOBCTL_TRAPPING_BIT altogether, it is
> not clear if we really need to hide this transition from debugger, WNOHANG
> after PTRACE_ATTACH can fail anyway if it races with SIGCONT.
> 
> Reported-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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