This is a note to let you know that I've just added the patch titled rcu/tree: Force quiescent state on callback overload to the 5.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: rcu-tree-force-quiescent-state-on-callback-overload.patch and it can be found in the queue-5.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit c493e686b5891a205c9c7f7b4dc8cdc1c9478255 Author: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx> Date: Mon Jun 22 00:07:27 2020 +0530 rcu/tree: Force quiescent state on callback overload [ Upstream commit 9c39245382de4d52a122641952900709d4a9950b ] On callback overload, it is necessary to quickly detect idle CPUs, and rcu_gp_fqs_check_wake() checks for this condition. Unfortunately, the code following the call to this function does not repeat this check, which means that in reality no actual quiescent-state forcing, instead only a couple of quick and pointless wakeups at the beginning of the grace period. This commit therefore adds a check for the RCU_GP_FLAG_OVLD flag in the post-wakeup "if" statement in rcu_gp_fqs_loop(). Fixes: 1fca4d12f4637 ("rcu: Expedite first two FQS scans under callback-overload conditions") Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Signed-off-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f78ee759af9cb..388a2ad292bf4 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1898,7 +1898,7 @@ static void rcu_gp_fqs_loop(void) break; /* If time for quiescent-state forcing, do it. */ if (!time_after(rcu_state.jiffies_force_qs, jiffies) || - (gf & RCU_GP_FLAG_FQS)) { + (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) { trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqsstart")); rcu_gp_fqs(first_gp_fqs);