lkml.org 
[lkml]   [2014]   [Dec]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 1/3] tracepoints: Do not use call_rcu_sched() before early_initcall()
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

In order to move enabling of trace events to just after mm_init(), the
tracepoint enable code can not use call_rcu_sched() because rcu isn't
even initialized yet. Since this can only happen before SMP is set up
(and even before interrupts are set up), there's no reason to use
call_rcu_sched() at this point.

Instead, create a variable called tracepoint_rcu_safe that gets enabled
via early_initcall() and if that is not set, free the code directly
instead of using call_rcu_sched().

This allows us to enable tracepoints early without issues.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/tracepoint.c | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 3490407dc7b7..9b90ef0ac731 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -33,6 +33,15 @@ extern struct tracepoint * const __stop___tracepoints_ptrs[];
/* Set to 1 to enable tracepoint debug output */
static const int tracepoint_debug;

+/*
+ * traceoint_rcu_is_safe is set to true at early_initcall().
+ * Tracepoints can be enabled before rcu is initialized.
+ * When that happens, there's no reason to free via call_rcu()
+ * because the system isn't even in SMP mode yet, and rcu isn't
+ * initialized. Just directly free the old tracepoints instead.
+ */
+static bool tracepoint_rcu_is_safe;
+
#ifdef CONFIG_MODULES
/*
* Tracepoint module list mutex protects the local module list.
@@ -76,7 +85,16 @@ static inline void release_probes(struct tracepoint_func *old)
if (old) {
struct tp_probes *tp_probes = container_of(old,
struct tp_probes, probes[0]);
- call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes);
+ /*
+ * Tracepoints can be enabled before RCU is initialized
+ * at boot up. If that is the case, do not bother using
+ * call_rcu() (because that will fail), but instead just
+ * free directly.
+ */
+ if (likely(tracepoint_rcu_is_safe))
+ call_rcu_sched(&tp_probes->rcu, rcu_free_old_probes);
+ else
+ rcu_free_old_probes(&tp_probes->rcu);
}
}

@@ -518,3 +536,10 @@ void syscall_unregfunc(void)
}
}
#endif
+
+static __init int init_tracepoint_rcu(void)
+{
+ tracepoint_rcu_is_safe = true;
+ return 0;
+}
+early_initcall(init_tracepoint_rcu);
--
2.1.3



\
 
 \ /
  Last update: 2014-12-14 18:21    [W:0.083 / U:0.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site