Ingo,
While testing my new code I stumbled upon this bug. This is a real
bug and has been in the kernel forever. Luckily, it's in a feature
that is seldom used. But it can cause a crash if the race is hit.
I based this off of my last pull request of tip/perf/urgent.
Thanks,
-- Steve
Please pull the latest tip/perf/urgent-2 tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/perf/urgent-2
Head SHA1: 740466bc89ad8bd5afcc8de220f715f62b21e365
Steven Rostedt (Red Hat) (1):
tracing: Fix free of probe entry by calling call_rcu_sched()
----
kernel/trace/ftrace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
---------------------------
commit 740466bc89ad8bd5afcc8de220f715f62b21e365
Author: Steven Rostedt (Red Hat) <rostedt@xxxxxxxxxxx>
Date: Wed Mar 13 11:15:19 2013 -0400
tracing: Fix free of probe entry by calling call_rcu_sched()
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: stable@xxxxxxxxxxxxxxx
Cc: Paul McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 98ca94a..e6effd0 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -3108,8 +3108,8 @@ __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();
--
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