linux-kernel - [PATCH -mm] markers: avoid call_rcu

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Message-ID: <4873CE05.2030001@redhat.com>
Date:	Tue, 08 Jul 2008 16:28:53 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	LKML <linux-kernel@...r.kernel.org>, Hideo AOKI <haoki@...hat.com>,
	Takahiro Yasui <tyasui@...hat.com>
Subject: [PATCH -mm] markers: avoid call_rcu_sched if old is NULL

Introduce marker_entry_free_old() and check old pointer is NULL before
setting call_rcu_sched(), because marker_entry_remove/add_probe() can
return NULL.

Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
---
 kernel/marker.c |   29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

Mathieu, I think this might be a bug. Tracepoint also has
same bug...

Index: 2.6.26-rc8-mm1/kernel/marker.c
===================================================================
--- 2.6.26-rc8-mm1.orig/kernel/marker.c	2008-07-07 11:42:04.000000000 -0400
+++ 2.6.26-rc8-mm1/kernel/marker.c	2008-07-07 11:42:04.000000000 -0400
@@ -201,6 +201,17 @@ static void free_old_closure(struct rcu_
 	entry->rcu_pending = 0;
 }

+static void marker_entry_free_old(struct marker_entry *entry, void *old)
+{
+	if (!old)
+		return;
+	entry->oldptr = old;
+	entry->rcu_pending = 1;
+	/* write rcu_pending before calling the RCU callback */
+	smp_wmb();
+	call_rcu_sched(&entry->rcu, free_old_closure);
+}
+
 static void debug_print_probes(struct marker_entry *entry)
 {
 	int i;
@@ -666,11 +677,7 @@ int marker_probe_register(const char *na
 	mutex_lock(&markers_mutex);
 	entry = get_marker(name);
 	WARN_ON(!entry);
-	entry->oldptr = old;
-	entry->rcu_pending = 1;
-	/* write rcu_pending before calling the RCU callback */
-	smp_wmb();
-	call_rcu_sched(&entry->rcu, free_old_closure);
+	marker_entry_free_old(entry, old);
 end:
 	mutex_unlock(&markers_mutex);
 	return ret;
@@ -709,11 +716,7 @@ int marker_probe_unregister(const char *
 	entry = get_marker(name);
 	if (!entry)
 		goto end;
-	entry->oldptr = old;
-	entry->rcu_pending = 1;
-	/* write rcu_pending before calling the RCU callback */
-	smp_wmb();
-	call_rcu_sched(&entry->rcu, free_old_closure);
+	marker_entry_free_old(entry, old);
 	remove_marker(name);	/* Ignore busy error message */
 	ret = 0;
 end:
@@ -787,11 +790,7 @@ int marker_probe_unregister_private_data
 	mutex_lock(&markers_mutex);
 	entry = get_marker_from_private_data(probe, probe_private);
 	WARN_ON(!entry);
-	entry->oldptr = old;
-	entry->rcu_pending = 1;
-	/* write rcu_pending before calling the RCU callback */
-	smp_wmb();
-	call_rcu_sched(&entry->rcu, free_old_closure);
+	marker_entry_free_old(entry, old);
 	remove_marker(entry->name);	/* Ignore busy error message */
 end:
 	mutex_unlock(&markers_mutex);
-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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