linux-kernel - Re: [PATCH RESEND 1/2] tracing: syscall_*regfunc() can race with copy

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Message-ID: <20140410133305.GA12228@redhat.com>
Date:	Thu, 10 Apr 2014 15:33:05 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH RESEND 1/2] tracing: syscall_*regfunc() can race with
	copy_process()

On 04/10, Steven Rostedt wrote:
>
> On Wed, 9 Apr 2014 19:05:42 +0200
> Oleg Nesterov <oleg@...hat.com> wrote:
>
> > syscall_regfunc() and syscall_unregfunc() should set/clear
> > TIF_SYSCALL_TRACEPOINT system-wide, but do_each_thread() can race
> > with copy_process() and miss the new child which was not added to
> > init_task.tasks list yet.
> >
> > Change copy_process() to update the child's TIF_SYSCALL_TRACEPOINT
> > under tasklist.
> >
> > While at it,
> >
> > 	- remove _irqsafe from syscall_regfunc/syscall_unregfunc,
> > 	  read_lock(tasklist) doesn't need to disable irqs.
> >
> > 	- change syscall_unregfunc() to check PF_KTHREAD to skip
> > 	  the kernel threads, ->mm != NULL is the common mistake.
> >
> > 	  Note: probably this check should be simply removed, needs
> > 	  another patch.
> >
> > Signed-off-by: Oleg Nesterov <oleg@...hat.com>
>
> BTW, how important is this fix? Something we should aim for the current
> merge window? stable? Or can it wait till 3.16?

I think this all can wait till 3.16. The problem is really minor.

Oleg.

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