[PATCH 4.4 11/11] rcu: Update documentation of rcu_read_unlock()

From: Greg Kroah-Hartman
Date: Sun Aug 08 2021 - 03:23:07 EST

From: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>

[ Upstream commit ec84b27f9b3b569f9235413d1945a2006b97b0aa ]

Since commit b4abf91047cf ("rtmutex: Make wait_lock irq safe") the
explanation in rcu_read_unlock() documentation about irq unsafe rtmutex
wait_lock is no longer valid.

Remove it to prevent kernel developers reading the documentation to rely on

Suggested-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: bigeasy@xxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20180525090507.22248-2-anna-maria@xxxxxxxxxxxxx
Signed-off-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>
Acked-by: Joe Korty <joe.korty@xxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
include/linux/rcupdate.h | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -880,9 +880,7 @@ static __always_inline void rcu_read_loc
* Unfortunately, this function acquires the scheduler's runqueue and
* priority-inheritance spinlocks. This means that deadlock could result
* if the caller of rcu_read_unlock() already holds one of these locks or
- * any lock that is ever acquired while holding them; or any lock which
- * can be taken from interrupt context because rcu_boost()->rt_mutex_lock()
- * does not disable irqs while taking ->wait_lock.
+ * any lock that is ever acquired while holding them.
* That said, RCU readers are never priority boosted unless they were
* preempted. Therefore, one way to avoid deadlock is to make sure