The rcu_torture_reader() drives RCU readers from interrupt context via smp_call_function_single(cpu, rcu_torture_irq, NULL, 0) with wait=0, to runs rcu_torture_irq() on a remote CPU. this is async, nothing waits for the remote handler to run.
On shutdown, torture_stop_kthread() only waits for each reader kthread to return, and the reader's timer_delete_sync() only drains its timer. Neither waits for a rcu_torture_irq() which still pending or executing on a remote CPU, so it can run after all readers have exited and rcu_torture_cleanup() has already advanced. 1. rcu_torture_irq() may issue cur_ops->call(rhp, rcu_torture_timer_cb) after cur_ops->cb_barrier() has been waiting for all outstanding callbacks complete. once the module is unloaded, fires into freed module text, a use-after-free happen. 2. rcu_torture_irq() may still be inside rcu_torture_one_read(), holding a read-side critical section, when cur_ops->cleanup() tears the flavor down (e.g. cleanup_srcu_struct()), triggering an active-reader warning or use-after-free of the torn-down structure. This commit therefore issue a kick_all_cpus_sync() after all readers kthread have returned and before cur_ops->cb_barrier(), synchronous IPI round trip to every CPU guarantees that every rcu_torture_irq() which previously issued by any reader has completed. Signed-off-by: Zqiang <[email protected]> --- kernel/rcu/rcutorture.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 4b4d9c70e827..f177ba9cb604 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -4476,6 +4476,8 @@ rcu_torture_cleanup(void) for (i = 0; i < nrealreaders; i++) torture_stop_kthread(rcu_torture_reader, reader_tasks[i]); + if (irqreader && cur_ops->irq_capable) + kick_all_cpus_sync(); kfree(reader_tasks); reader_tasks = NULL; } -- 2.17.1
