Hello, On Wed, Jan 31, 2024 at 08:27:45PM +0100, Helge Deller wrote: > When hot-unplugging a 32-bit CPU on the parisc platform with > "chcpu -d 1", I get the following kernel panic. Adding a check > for !pwq prevents the panic. > > Kernel Fault: Code=26 (Data memory access rights trap) at addr 00000000 > CPU: 1 PID: 21 Comm: cpuhp/1 Not tainted 6.8.0-rc1-32bit+ #1291 > Hardware name: 9000/778/B160L > > IASQ: 00000000 00000000 IAOQ: 10446db4 10446db8 > IIR: 0f80109c ISR: 00000000 IOR: 00000000 > CPU: 1 CR30: 11dd1710 CR31: 00000000 > IAOQ[0]: wq_update_pod+0x98/0x14c > IAOQ[1]: wq_update_pod+0x9c/0x14c > RP(r2): wq_update_pod+0x80/0x14c > Backtrace: > [<10448744>] workqueue_offline_cpu+0x1d4/0x1dc > [<10429db4>] cpuhp_invoke_callback+0xf8/0x200 > [<1042a1d0>] cpuhp_thread_fun+0xb8/0x164 > [<10452970>] smpboot_thread_fn+0x284/0x288 > [<1044d8f4>] kthread+0x12c/0x13c > [<1040201c>] ret_from_kernel_thread+0x1c/0x24 > Kernel panic - not syncing: Kernel Fault > > Signed-off-by: Helge Deller <deller@xxxxxx> > > --- > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 76e60faed892..dfeee7b7322c 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -4521,6 +4521,8 @@ static void wq_update_pod(struct workqueue_struct *wq, int cpu, > wq_calc_pod_cpumask(target_attrs, cpu, off_cpu); > pwq = rcu_dereference_protected(*per_cpu_ptr(wq->cpu_pwq, cpu), > lockdep_is_held(&wq_pool_mutex)); > + if (!pwq) > + return; Hmm... I have a hard time imagining a scenario where some CPUs don't have pwq installed on wq->cpu_pwq. Can you please run `drgn tools/workqueue/wq_dump.py` before triggering the hotplug event and paste the output along with full dmesg? Thanks. -- tejun
