Commit d4e287d7 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Frederic Weisbecker
Browse files

rcu-tasks: Remove open-coded one-byte cmpxchg() emulation 



This commit removes the open-coded one-byte cmpxchg() emulation from
rcu_trc_cmpxchg_need_qs(), replacing it with just cmpxchg() given the
latter's new-found ability to handle single-byte arguments across all
architectures.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Reviewed-by: default avatarNeeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
parent 0a116dc8

kernel/rcu/tasks.h

+1 −16
Original line number Diff line number Diff line
@@ -1541,22 +1541,7 @@ static void rcu_st_need_qs(struct task_struct *t, u8 v) 
 */

u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new)

{

	union rcu_special ret;

	union rcu_special trs_old = READ_ONCE(t->trc_reader_special);

	union rcu_special trs_new = trs_old;



	if (trs_old.b.need_qs != old)

		return trs_old.b.need_qs;

	trs_new.b.need_qs = new;



	// Although cmpxchg() appears to KCSAN to update all four bytes,

	// only the .b.need_qs byte actually changes.

	instrument_atomic_read_write(&t->trc_reader_special.b.need_qs,

				     sizeof(t->trc_reader_special.b.need_qs));

	// Avoid false-positive KCSAN failures.

	ret.s = data_race(cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s));



	return ret.b.need_qs;

	return cmpxchg(&t->trc_reader_special.b.need_qs, old, new);

}

EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs);