Commit 49f5903b authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Move preemption disabling out of __srcu_read_lock() 



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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 7f21aeef

include/linux/srcu.h

+4 −1
Original line number Diff line number Diff line
@@ -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;

}

kernel/exit.c

+2 −0
Original line number Diff line number Diff line
@@ -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

kernel/rcu/srcu.c

+0 −2
Original line number Diff line number Diff line
@@ -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);

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