linux-kernel - Re: [PATCH v2 5/5] perf: Enable applicable siblings when group leader is enable-on-exec

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Date:	Wed, 23 Nov 2011 12:39:42 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Deng-Cheng Zhu <dczhu@...s.com>
Cc:	"Barzilay, Eyal" <eyal@...s.com>,
	"Fortuna, Zenon" <zenon@...s.com>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] perf: Enable applicable siblings when group
 leader is enable-on-exec

On Wed, 2011-11-23 at 11:38 +0800, Deng-Cheng Zhu wrote:

> +	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
> +		ret = event_enable_on_exec(event, ctx);
> +		if (ret)
> +			enabled = 1;
> +	}
> +
>   	list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
>   		ret = event_enable_on_exec(event, ctx);
>   		if (ret)

This isn't correct either, in this case you should then remove the other
two iterations of pinned/flexible group lists.

Also your use of list_for_each_entry_rcu() is incorrect, either you then
should also use rcu_read_lock(), or its not needed and not use the _rcu
list primitive at all.

Now since event_list is modified under ctx->lock, and we hold that lock
no fancy stuff is needed and we can do without.

---
Subject: perf: Fix enable_on_exec for sibling events
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Tue Nov 22 11:25:43 CET 2011

Deng-Cheng Zhu reported that sibling events that were created disabled
with enable_on_exec would never get enabled. Iterate all events instead
of the group lists.

Reported-by: Deng-Cheng Zhu <dczhu@...s.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/n/tip-299rxrpmmle8hp3spyxfo202@git.kernel.org
---
 kernel/events/core.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

Index: linux-2.6/kernel/events/core.c
===================================================================
--- linux-2.6.orig/kernel/events/core.c
+++ linux-2.6/kernel/events/core.c
@@ -2494,13 +2494,7 @@ static void perf_event_enable_on_exec(st
 	raw_spin_lock(&ctx->lock);
 	task_ctx_sched_out(ctx);
 
-	list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
-		ret = event_enable_on_exec(event, ctx);
-		if (ret)
-			enabled = 1;
-	}
-
-	list_for_each_entry(event, &ctx->flexible_groups, group_entry) {
+	list_for_each_entry(event, &ctx->event_list, group_entry) {
 		ret = event_enable_on_exec(event, ctx);
 		if (ret)
 			enabled = 1;

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