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Subject[PATCH] RCU: implement rcu_read_[un]lock_preempt()
With the introduction of preemptible RCU, RCU doesn't gurantee that
its critical section runs on the CPU it started to run. As there are
cases where non-preemptible RCU critical section makes sense, create
new RCU read lock variants which turns of preemption -
rcu_read_[un]lock_preempt() which are identical to rcu_read_[un]lock()
for classic implementation and have enclosing preempt disable/enable
for preemptible RCU.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
This will be used by following block layer updates. If this and the
block changes get acked, it'll be best to push this through block
tree.

Thanks.

include/linux/rcuclassic.h | 2 ++
include/linux/rcupdate.h | 18 ++++++++++++++++++
include/linux/rcupreempt.h | 6 ++++--
3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index b3aa05b..08c6153 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -136,6 +136,8 @@ extern struct lockdep_map rcu_lock_map;
__release(RCU); \
preempt_enable(); \
} while (0)
+#define __rcu_read_lock_preempt() __rcu_read_lock()
+#define __rcu_read_unlock_preempt() __rcu_read_unlock()
#define __rcu_read_lock_bh() \
do { \
local_bh_disable(); \
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index d42dbec..e0e3486 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -112,6 +112,24 @@ struct rcu_head {
#define rcu_read_unlock() __rcu_read_unlock()

/**
+ * rcu_read_lock_preempt - mark the beginning of non-preemptible RCU
+ * critical section
+ *
+ * Identical to rcu_read_lock() but the critical section is guaranteed
+ * to be non-preemptible. Note that this is identical to
+ * rcu_read_lock() on classic RCU implementation.
+ */
+#define rcu_read_lock_preempt() __rcu_read_lock_preempt()
+
+/**
+ * rcu_read_unlock_preempt - mark the end of of non-preemptible RCU
+ * critical section
+ *
+ * See rcu_read_lock_preempt() for more information.
+ */
+#define rcu_read_unlock_preempt() __rcu_read_unlock_preempt()
+
+/**
* rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
*
* This is equivalent of rcu_read_lock(), but to be used when updates
diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h
index 8a05c7e..b263ceb 100644
--- a/include/linux/rcupreempt.h
+++ b/include/linux/rcupreempt.h
@@ -49,8 +49,10 @@ extern void __rcu_read_unlock(void) __releases(RCU);
extern int rcu_pending(int cpu);
extern int rcu_needs_cpu(int cpu);

-#define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); }
-#define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); }
+#define __rcu_read_lock_preempt() { rcu_read_lock(); preempt_disable(); }
+#define __rcu_read_unlock_preempt() { preempt_enable(); rcu_read_unlock(); }
+#define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); }
+#define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); }

extern void __synchronize_sched(void);

--
1.5.4.5


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