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rcu: Add _notrace variation of rcu_dereference_raw() and hlist_for_each_entry_rcu()

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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 <paulmck@linux.vnet.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2013-05-28 14:38:42 -04:00
parent 6721cb6002
commit 12bcbe66d7
2 changed files with 29 additions and 0 deletions
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9
include/linux/rcupdate.h
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@ -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