[PATCH tip/core/rcu 07/13] rcu: Move preemption disabling out of __srcu_read_lock()

[Paul E. McKenney]

Currently, __srcu_read_lock() cannot be invoked from restricted
environments because it contains calls to preempt_disable() and
preempt_enable(), both of which can invoke lockdep, which is a bad
idea in some restricted execution modes.  This commit therefore moves
the preempt_disable() and preempt_enable() from __srcu_read_lock()
to srcu_read_lock().  It also inserts the preempt_disable() and
preempt_enable() around the call to __srcu_read_lock() in do_exit().

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
 include/linux/srcu.h | 5 ++++-
 kernel/exit.c        | 2 ++
 kernel/rcu/srcu.c    | 2 --
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index bdeb4567b71e..f5f80c5643ac 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -215,8 +215,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
  */
 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 {
-	int retval = __srcu_read_lock(sp);
+	int retval;
 
+	preempt_disable();
+	retval = __srcu_read_lock(sp);
+	preempt_enable();
 	rcu_lock_acquire(&(sp)->dep_map);
 	return retval;
 }
diff --git a/kernel/exit.c b/kernel/exit.c
index ea95ee1b5ef7..0e93b63bbc59 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -761,7 +761,9 @@ void do_exit(long code)
 	 */
 	flush_ptrace_hw_breakpoint(tsk);
 
+	TASKS_RCU(preempt_disable());
 	TASKS_RCU(tasks_rcu_i = __srcu_read_lock(&tasks_rcu_exit_srcu));
+	TASKS_RCU(preempt_enable());
 	exit_notify(tsk, group_dead);
 	proc_exit_connector(tsk);
 #ifdef CONFIG_NUMA
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index 9e6122540d28..a63a1ea5a41b 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -298,11 +298,9 @@ int __srcu_read_lock(struct srcu_struct *sp)
 	int idx;
 
 	idx = READ_ONCE(sp->completed) & 0x1;
-	preempt_disable();
 	__this_cpu_inc(sp->per_cpu_ref->c[idx]);
 	smp_mb(); /* B */  /* Avoid leaking the critical section. */
 	__this_cpu_inc(sp->per_cpu_ref->seq[idx]);
-	preempt_enable();
 	return idx;
 }
 EXPORT_SYMBOL_GPL(__srcu_read_lock);
-- 
2.5.2

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