Le Thu, Dec 12, 2024 at 10:42:14AM -0800, Paul E. McKenney a écrit : > From: Frederic Weisbecker <frederic@xxxxxxxxxx> > > After a CPU has set itself offline and before it eventually calls > rcutree_report_cpu_dead(), there are still opportunities for callbacks > to be enqueued, for example from an IRQ. When that happens on NOCB, the > rcuog wake-up is deferred through an IPI to an online CPU in order not > to call into the scheduler and risk arming the RT-bandwidth after > hrtimers have been migrated out and disabled. > > But performing a synchronized IPI from an IRQ is buggy as reported in > the following scenario: > > WARNING: CPU: 1 PID: 26 at kernel/smp.c:633 smp_call_function_single > Modules linked in: rcutorture torture > CPU: 1 UID: 0 PID: 26 Comm: migration/1 Not tainted 6.11.0-rc1-00012-g9139f93209d1 #1 > Stopper: multi_cpu_stop+0x0/0x320 <- __stop_cpus+0xd0/0x120 > RIP: 0010:smp_call_function_single > <IRQ> > swake_up_one_online > __call_rcu_nocb_wake > __call_rcu_common > ? rcu_torture_one_read > call_timer_fn > __run_timers > run_timer_softirq > handle_softirqs > irq_exit_rcu > ? tick_handle_periodic > sysvec_apic_timer_interrupt > </IRQ> > > The periodic tick must be shutdown when the CPU is offline, just like is > done for oneshot tick. This must be fixed but this is not enough: > softirqs can happen on any hardirq tail and reproduce the above scenario. > > Fix this with introducing a special deferred rcuog wake up mode when the > CPU is offline. This deferred wake up doesn't arm any timer and simply > wait for rcu_report_cpu_dead() to be called in order to flush any > pending rcuog wake up. > > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> > Closes: https://lore.kernel.org/oe-lkp/202409231644.4c55582d-lkp@xxxxxxxxx > Fixes: 9139f93209d1 ("rcu/nocb: Fix RT throttling hrtimer armed from offline CPU") > Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> You can drop this patch, it has been replaced with another version upstream. Thanks!
