[stable,5.15/5.10,0/2] rcu-tasks: Idle tasks on offline CPUs are in quiescent states

Message

Krister Johansen Nov. 22, 2024, 8:46 a.m. UTC

Paul, Neeraj, and Stable Team:
I've run into a case with rcu_tasks_postscan where the warning introduced as
part of 46aa886c4("rcu-tasks: Fix IPI failure handling in
trc_wait_for_one_reader") is getting triggered when trc_wait_for_one_reader
sends an IPI to a CPU that is offline.  This is occurring on a platform that has
hotplug slots available but not populated.  I don't believe the bug is caused by
this change, but I do think that Paul's commit that confines the postscan
operation to just the active CPUs would help prevent this from happening.

Would the RCU maintainers be amenable to having this patch backported to the
5.10 and 5.15 branches as well?  I've attached cherry-picks of the relevant
commits to minimize the additional work needed.

Thanks,

-K

Paul E. McKenney (1):
  rcu-tasks: Idle tasks on offline CPUs are in quiescent states

 kernel/rcu/tasks.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)