On Thu, Apr 09, 2026 at 01:10:14PM -0700, Paul E. McKenney wrote: > On Thu, Apr 09, 2026 at 09:15:50PM +0200, Vasily Gorbik wrote:
[ . . . ] > > Yes, tested on s390 LPAR (76 online, 400 possible) as well as > > on x86 KVM with --smp 16,maxcpus=255 and CONFIG_NR_CPUS=256 > > no more workqueue lockup in both cases. > > > > Thank you! > > > > Tested-by: Vasily Gorbik <[email protected]> > > Thank you for testing this! > > Please see below for an updated patch. Tejun's patch might obsolete > this one, but just in case he balks at SRCU queueing handlers for CPUs > that are not even in the cpu_possible_mask. ;-) And because we don't invoke SRCU callbacks on CPUs that are not yet fully online, such CPUs had better not invoke call_srcu(), synchronize_srcu(), or synchronize_srcu_expedited() on a CPU that is not yet fully online. I am therefore adding the warning shown below. Better paranoid late than paranoid not at all. ;-) Thanx, Paul ------------------------------------------------------------------------ diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index a67af44fc0745..d62509efb52f5 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1431,6 +1431,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rcu_callback_t func, bool do_norm) { + WARN_ON_ONCE(!rcu_cpu_beenfullyonline(raw_smp_processor_id())); if (debug_rcu_head_queue(rhp)) { /* Probable double call_srcu(), so leak the callback. */ WRITE_ONCE(rhp->func, srcu_leak_callback);
