From 12bcbe66d7b3cc9f9f86cd02f925666eaa3c2107 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Tue, 28 May 2013 14:38:42 -0400 Subject: rcu: Add _notrace variation of rcu_dereference_raw() and hlist_for_each_entry_rcu() As rcu_dereference_raw() under RCU debug config options can add quite a bit of checks, and that tracing uses rcu_dereference_raw(), these checks happen with the function tracer. The function tracer also happens to trace these debug checks too. This added overhead can livelock the system. Add a new interface to RCU for both rcu_dereference_raw_notrace() as well as hlist_for_each_entry_rcu_notrace() as the hlist iterator uses the rcu_dereference_raw() as well, and is used a bit with the function tracer. Link: http://lkml.kernel.org/r/20130528184209.304356745@goodmis.org Acked-by: Paul E. McKenney Signed-off-by: Steven Rostedt --- include/linux/rculist.h | 20 ++++++++++++++++++++ include/linux/rcupdate.h | 9 +++++++++ 2 files changed, 29 insertions(+) diff --git a/include/linux/rculist.h b/include/linux/rculist.h index 8089e35d47ac..f4b1001a4676 100644 --- a/include/linux/rculist.h +++ b/include/linux/rculist.h @@ -460,6 +460,26 @@ static inline void hlist_add_after_rcu(struct hlist_node *prev, pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\ &(pos)->member)), typeof(*(pos)), member)) +/** + * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing) + * @pos: the type * to use as a loop cursor. + * @head: the head for your list. + * @member: the name of the hlist_node within the struct. + * + * This list-traversal primitive may safely run concurrently with + * the _rcu list-mutation primitives such as hlist_add_head_rcu() + * as long as the traversal is guarded by rcu_read_lock(). + * + * This is the same as hlist_for_each_entry_rcu() except that it does + * not do any RCU debugging or tracing. + */ +#define hlist_for_each_entry_rcu_notrace(pos, head, member) \ + for (pos = hlist_entry_safe (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\ + typeof(*(pos)), member); \ + pos; \ + pos = hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\ + &(pos)->member)), typeof(*(pos)), member)) + /** * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type * @pos: the type * to use as a loop cursor. diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 4ccd68e49b00..ddcc7826d907 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -640,6 +640,15 @@ static inline void rcu_preempt_sleep_check(void) #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ +/* + * The tracing infrastructure traces RCU (we want that), but unfortunately + * some of the RCU checks causes tracing to lock up the system. + * + * The tracing version of rcu_dereference_raw() must not call + * rcu_read_lock_held(). + */ +#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu) + /** * rcu_access_index() - fetch RCU index with no dereferencing * @p: The index to read -- cgit v1.2.3