On Tue, Apr 14, 2026 at 12:24:12PM -0700, Paul E. McKenney wrote: > On Thu, Apr 09, 2026 at 09:03:26PM -0700, Paul E. McKenney wrote: > Please see below for the full patch, including refraining from queueing > workqueue handlers on not-yet-online CPUs and diverting SRCU callbacks > from not-yet-fully-online CPUs to the boot CPU's callback queue. ... > commit ce533a60b2ef29a9b516cc717e77c6b679bc09c0 > Author: Paul E. McKenney <[email protected]> > Date: Thu Apr 9 11:16:02 2026 -0700 > > srcu: Don't queue workqueue handlers to never-online CPUs > > While an srcu_struct structure is in the midst of switching from CPU-0 > to all-CPUs state, it can attempt to invoke callbacks for CPUs that > have never been online. Worse yet, it can attempt in invoke callbacks > for CPUs that never will be online due to not being present in the > cpu_possible_mask. This can cause hangs on s390, which is not set up to > deal with workqueue handlers being scheduled on such CPUs. This commit > therefore causes Tree SRCU to refrain from queueing workqueue handlers > on CPUs that have not yet (and might never) come online. > > Because callbacks are not invoked on CPUs that have not been > online, it is an error to invoke call_srcu(), synchronize_srcu(), or > synchronize_srcu_expedited() on a CPU that is not yet fully online. > However, it turns out to be less code to redirect the callbacks > from too-early invocations of call_srcu() than to warn about such > invocations. This commit therefore also redirects callbacks queued on > not-yet-fully-online CPUs to the boot CPU. > > Reported-by: Vasily Gorbik <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > Tested-by: Vasily Gorbik <[email protected]> > Cc: Tejun Heo <[email protected]>
I retested it on s390 and on x86 KVM with --smp 16,maxcpus=255, all looks good to me. FWIW, again: Tested-by: Vasily Gorbik <[email protected]> Would you mind adding Cc: stable so it gets picked up for v7.0? 61bbcfb50514 ("srcu: Push srcu_node allocation to GP when non-preemptible") is what made it reproducible for us. Thank you!
