Hello, Paul. On Wed, Apr 26, 2023 at 10:26:38AM -0700, Paul E. McKenney wrote: > The rcu_tasks_invoke_cbs() relies on queue_work_on() to silently fall > back to WORK_CPU_UNBOUND when the specified CPU is offline. However, > the queue_work_on() function's silent fallback mechanism relies on that > CPU having been online at some time in the past. When queue_work_on() > is passed a CPU that has never been online, workqueue lockups ensue, > which can be bad for your kernel's general health and well-being. > > This commit therefore checks whether a given CPU is currently online, > and, if not substitutes WORK_CPU_UNBOUND in the subsequent call to > queue_work_on(). Why not simply omit the queue_work_on() call entirely? > Because this function is flooding callback-invocation notifications > to all CPUs, and must deal with possibilities that include a sparse > cpu_possible_mask. > > Fixes: d363f833c6d88 rcu-tasks: Use workqueues for multiple rcu_tasks_invoke_cbs() invocations > Reported-by: Tejun Heo <tj@xxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> I don't understand the code at all but wonder whether it can do sth similar to cpumask_any_distribute() which RR's through the specified cpumask. Would it make sense to change rcu_tasks_invoke_cbs() to do something similar against cpu_online_mask? Thanks. -- tejun
