The two READ_ONCEs here imply that there might be updater concurrently modifies rcu_read_lock_nesting, although it's true there could be interrupt handlers enter rcu RSCS, but rcu_read_lock_nesting should remain unchanged after they finished. That is, READ_ONCE and then WRITE_ONCE the same variable is not a valid pattern, this patch thus removes the two READ_ONCEs.
Signed-off-by: Alan Huang <[email protected]> --- kernel/rcu/tree_plugin.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 340bbefe5f65..c90edbb7fa40 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -376,12 +376,12 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) static void rcu_preempt_read_enter(void) { - WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1); + WRITE_ONCE(current->rcu_read_lock_nesting, current->rcu_read_lock_nesting + 1); } static int rcu_preempt_read_exit(void) { - int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1; + int ret = current->rcu_read_lock_nesting - 1; WRITE_ONCE(current->rcu_read_lock_nesting, ret); return ret; -- 2.34.1
