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SubjectRe: [PATCH] rcu: Remove unnecessary updates to ret in rcu_gp_fqs_loop
On Tue, Jun 29, 2021 at 09:55:51PM +0800, Liu Song wrote:
> From: Liu Song <liu.song11@zte.com.cn>
>
> The ret value will be updated in the subsequent process,
> so there is no need to update it here.
>
> Signed-off-by: Liu Song <liu.song11@zte.com.cn>

Good eyes, and it is safe to say that rcutorture would never have found
that one. ;-)

As usual, I could not resist the urge to edit the commit log, and I also
added the "(void)" to indicate that the code intends to ignore the return
value, as it now uses elapsed time to make its decisions.

Please let me know if I messed anything up.

Thanx, Paul

------------------------------------------------------------------------

commit 48434fc6700c31bd258713c24b78053fe47d393e
Author: Liu Song <liu.song11@zte.com.cn>
Date: Tue Jun 29 21:55:51 2021 +0800

rcu: Remove useless "ret" update in rcu_gp_fqs_loop()

Within rcu_gp_fqs_loop(), the "ret" local variable is set to the
return value from swait_event_idle_timeout_exclusive(), but "ret" is
unconditionally overwritten later in the code. This commit therefore
removes this useless assignment.

Signed-off-by: Liu Song <liu.song11@zte.com.cn>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 35ed10bb95ef..a627a200a5ae 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1958,8 +1958,8 @@ static noinline_for_stack void rcu_gp_fqs_loop(void)
trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
TPS("fqswait"));
WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
- ret = swait_event_idle_timeout_exclusive(
- rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
+ (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
+ rcu_gp_fqs_check_wake(&gf), j);
rcu_gp_torture_wait();
WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
/* Locking provides needed memory barriers. */
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