linux-kernel - Re: [RFC PATCH 1/5] powerpc: Syscall hooks for context tracking subsystem

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Date:	Thu, 7 Feb 2013 17:09:43 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	paulmck@...ux.vnet.ibm.com, benh@...nel.crashing.org,
	paulus@...ba.org
Subject: Re: [RFC PATCH 1/5] powerpc: Syscall hooks for context tracking subsystem

2013/2/7 Li Zhong <zhong@...ux.vnet.ibm.com>:
> On Thu, 2013-02-07 at 01:29 +0100, Frederic Weisbecker wrote:
>> In x86-64, schedule_user() and do_notify_resume() can be called before
>> syscall_trace_leave(). As a result we may be entering
>> syscall_trace_leave() in user mode (from a context tracking POV). To
>> fix this I added a call to user_exit() on the very beginning of that
>> function.
>>
>> You can find the details in 2c5594df344cd1ff0cc9bf007dea3235582b3acf
>> ("rcu: Fix unrecovered RCU user mode in syscall_trace_leave()").
>
> Hi Frederic,
>
> Thank you very much for the reminding.
>
>>
>> Could this problem happen in ppc as well?
>
> I checked the code(64 bit) today, it seems to me that it won't happen.
> But fortunately, we are in the ppc mailing list, please correct me if my
> understanding is wrong.

Ah indeed. Looking at syscall_exit_work label in entry_64.S,
do_syscall_trace_leave is called before ret_from_except which is where
we handle user preemption and do_notify_resume. So that looks fine.

>
> By the way, I enabled CONTEXT_TRACKING_FORCE and PROVE_RCU, so if it
> could happen, I think there should be some illegal RCU usage complaints
> reported.

Ok.

Thanks.
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