[2.6.32-rc5-git5] synchronize_sched() inside spin_lock()?

[2.6.32-rc5-git5] synchronize_sched() inside spin_lock()?

[Tetsuo Handa]

Commit: 4ea7e38696c7e798c47ebbecadfd392f23f814f9

tracepoint_synchronize_unregister() calls synchronize_sched(), but it is
between spin_lock() and spin_unlock(). Is it OK?

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();

		/*
		 * Clean the device list
		 */
		list_for_each_entry_safe(new_stat, temp, &hw_stats_list, list) {
			if (new_stat->dev == NULL) {
				list_del_rcu(&new_stat->list);
				call_rcu(&new_stat->rcu, free_dm_hw_stat);
			}
		}
		break;
	default:
		rc = 1;
		break;
	}

	if (!rc)
		trace_state = state;

	spin_unlock(&trace_state_lock);

	if (rc)
		return -EINPROGRESS;
	return rc;
}

Re: [2.6.32-rc5-git5] synchronize_sched() inside spin_lock()?

[Paul E. McKenney]

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();
> 
> 		/*
> 		 * Clean the device list
> 		 */
> 		list_for_each_entry_safe(new_stat, temp, &hw_stats_list, list) {
> 			if (new_stat->dev == NULL) {
> 				list_del_rcu(&new_stat->list);
> 				call_rcu(&new_stat->rcu, free_dm_hw_stat);
> 			}
> 		}
> 		break;
> 	default:
> 		rc = 1;
> 		break;
> 	}
> 
> 	if (!rc)
> 		trace_state = state;
> 
> 	spin_unlock(&trace_state_lock);
> 
> 	if (rc)
> 		return -EINPROGRESS;
> 	return rc;
> }
> --
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Re: [2.6.32-rc5-git5] synchronize_sched() inside spin_lock()?

[Dmitry Torokhov]

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

Re: [2.6.32-rc5-git5] synchronize_sched() inside spin_lock()?

[Paul E. McKenney]

On Mon, Nov 02, 2009 at 03:33:46PM -0800, Dmitry Torokhov wrote:
> 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.

Ah!  That would indeed be bad.

							Thanx, Paul

[2.6.32-rc8] set_all_monitor_traces() sleeping bug.

[Tetsuo Handa]

Commit: 4ea7e38696c7e798c47ebbecadfd392f23f814f9

set_all_monitor_traces() calls tracepoint_synchronize_unregister()
with a spinlock held, but tracepoint_synchronize_unregister() may sleep.

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();

		/*
		 * Clean the device list
		 */
		list_for_each_entry_safe(new_stat, temp, &hw_stats_list, list) {
			if (new_stat->dev == NULL) {
				list_del_rcu(&new_stat->list);
				call_rcu(&new_stat->rcu, free_dm_hw_stat);
			}
		}
		break;
	default:
		rc = 1;
		break;
	}

	if (!rc)
		trace_state = state;

	spin_unlock(&trace_state_lock);

	if (rc)
		return -EINPROGRESS;
	return rc;
}