linux-kernel - Re: [2.6.32-rc5-git5] synchronize_sched() inside spin

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Message-Id: <200911021533.46413.dmitry.torokhov@gmail.com>
Date:	Mon, 2 Nov 2009 15:33:46 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	nhorman@...driver.com, linux-kernel@...r.kernel.org
Subject: Re: [2.6.32-rc5-git5] synchronize_sched() inside spin_lock()?

On Monday 02 November 2009 02:30:28 pm Paul E. McKenney wrote:
> On Mon, Nov 02, 2009 at 09:00:06PM +0900, Tetsuo Handa wrote:
> > Commit: 4ea7e38696c7e798c47ebbecadfd392f23f814f9
> >
> > tracepoint_synchronize_unregister() calls synchronize_sched(), but it is
> > between spin_lock() and spin_unlock(). Is it OK?
> 
> Calling synchronize_sched() while holding a spinlock would indeed be
> very bad, but the code below seems to instead be invoking call_rcu(),
> which is no problem.
> 
> Or am I missing something here?
> 
> 							Thanx, Paul
> 
> > static int set_all_monitor_traces(int state)
> > {
> > 	int rc = 0;
> > 	struct dm_hw_stat_delta *new_stat = NULL;
> > 	struct dm_hw_stat_delta *temp;
> >
> > 	spin_lock(&trace_state_lock);
> >
> > 	switch (state) {
> > 	case TRACE_ON:
> > 		rc |= register_trace_kfree_skb(trace_kfree_skb_hit);
> > 		rc |= register_trace_napi_poll(trace_napi_poll_hit);
> > 		break;
> > 	case TRACE_OFF:
> > 		rc |= unregister_trace_kfree_skb(trace_kfree_skb_hit);
> > 		rc |= unregister_trace_napi_poll(trace_napi_poll_hit);
> >
> > 		tracepoint_synchronize_unregister();

This has synchronize_sched() inside.


-- 
Dmitry
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