[ 3.5.y.z extended stable ] Patch "tracing: Fix free of probe entry by calling call_rcu_sched()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    tracing: Fix free of probe entry by calling call_rcu_sched()

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 44ef71022419362427dd888e1bff079574c30db1 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt at goodmis.org>
Date: Wed, 13 Mar 2013 11:15:19 -0400
Subject: [PATCH] tracing: Fix free of probe entry by calling call_rcu_sched()

commit 740466bc89ad8bd5afcc8de220f715f62b21e365 upstream.

Because function tracing is very invasive, and can even trace
calls to rcu_read_lock(), RCU access in function tracing is done
with preempt_disable_notrace(). This requires a synchronize_sched()
for updates and not a synchronize_rcu().

Function probes (traceon, traceoff, etc) must be freed after
a synchronize_sched() after its entry has been removed from the
hash. But call_rcu() is used. Fix this by using call_rcu_sched().

Also fix the usage to use hlist_del_rcu() instead of hlist_del().

Cc: Paul McKenney <paulmck at linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt <rostedt at goodmis.org>
Luis Henriques <luis.henriques at canonical.com>
---
 kernel/trace/ftrace.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index e5a77ba..1b6ec54 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3002,8 +3002,8 @@ __unregister_ftrace_function_probe(char *glob, struct ftrace_probe_ops *ops,
 					continue;
 			}

-			hlist_del(&entry->node);
-			call_rcu(&entry->rcu, ftrace_free_entry_rcu);
+			hlist_del_rcu(&entry->node);
+			call_rcu_sched(&entry->rcu, ftrace_free_entry_rcu);
 		}
 	}
 	__disable_ftrace_function_probe();
--
1.8.1.2