3.10.97-rt107-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Andrzej Siewior With completion using swait and so rawlocks we don't need this anymore. Further, bisect thinks this patch is responsible for: |BUG: unable to handle kernel NULL pointer dereference at (null) |IP: [] sched_cpu_active+0x53/0x70 |PGD 0 |Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC |Dumping ftrace buffer: | (ftrace buffer empty) |Modules linked in: |CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.4.1+ #330 |Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Debian-1.8.2-1 04/01/2014 |task: ffff88013ae64b00 ti: ffff88013ae74000 task.ti: ffff88013ae74000 |RIP: 0010:[] [] sched_cpu_active+0x53/0x70 |RSP: 0000:ffff88013ae77eb8 EFLAGS: 00010082 |RAX: 0000000000000001 RBX: ffffffff81c2cf20 RCX: 0000001050fb52fb |RDX: 0000001050fb52fb RSI: 000000105117ca1e RDI: 00000000001c7723 |RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001 |R10: 0000000000000000 R11: 0000000000000001 R12: 00000000ffffffff |R13: ffffffff81c2cee0 R14: 0000000000000000 R15: 0000000000000001 |FS: 0000000000000000(0000) GS:ffff88013b200000(0000) knlGS:0000000000000000 |CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b |CR2: 0000000000000000 CR3: 0000000001c09000 CR4: 00000000000006e0 |Stack: | ffffffff810c446d ffff88013ae77f00 ffffffff8107d8dd 000000000000000a | 0000000000000001 0000000000000000 0000000000000000 0000000000000000 | 0000000000000000 ffff88013ae77f10 ffffffff8107d90e ffff88013ae77f20 |Call Trace: | [] ? debug_lockdep_rcu_enabled+0x1d/0x20 | [] ? notifier_call_chain+0x5d/0x80 | [] ? __raw_notifier_call_chain+0xe/0x10 | [] ? cpu_notify+0x23/0x40 | [] ? notify_cpu_starting+0x28/0x30 during hotplug. The rawlocks need to remain however. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt --- kernel/stop_machine.c | 38 +++++++------------------------------- 1 file changed, 7 insertions(+), 31 deletions(-) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 5f02a3fe729f..652fea4b0c83 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -29,7 +29,7 @@ struct cpu_stop_done { atomic_t nr_todo; /* nr left to execute */ bool executed; /* actually executed? */ int ret; /* collected return value */ - struct task_struct *waiter; /* woken when nr_todo reaches 0 */ + struct completion completion; /* fired if nr_todo reaches 0 */ }; /* the actual stopper, one per every possible cpu, enabled on online cpus */ @@ -47,7 +47,7 @@ static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo) { memset(done, 0, sizeof(*done)); atomic_set(&done->nr_todo, nr_todo); - done->waiter = current; + init_completion(&done->completion); } /* signal completion unless @done is NULL */ @@ -56,10 +56,8 @@ static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed) if (done) { if (executed) done->executed = true; - if (atomic_dec_and_test(&done->nr_todo)) { - wake_up_process(done->waiter); - done->waiter = NULL; - } + if (atomic_dec_and_test(&done->nr_todo)) + complete(&done->completion); } } @@ -82,22 +80,6 @@ static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work) raw_spin_unlock_irqrestore(&stopper->lock, flags); } -static void wait_for_stop_done(struct cpu_stop_done *done) -{ - set_current_state(TASK_UNINTERRUPTIBLE); - while (atomic_read(&done->nr_todo)) { - schedule(); - set_current_state(TASK_UNINTERRUPTIBLE); - } - /* - * We need to wait until cpu_stop_signal_done() has cleared - * done->waiter. - */ - while (done->waiter) - cpu_relax(); - set_current_state(TASK_RUNNING); -} - /** * stop_one_cpu - stop a cpu * @cpu: cpu to stop @@ -129,7 +111,7 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) cpu_stop_init_done(&done, 1); cpu_stop_queue_work(cpu, &work); - wait_for_stop_done(&done); + wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT; } @@ -195,7 +177,7 @@ static int __stop_cpus(const struct cpumask *cpumask, cpu_stop_init_done(&done, cpumask_weight(cpumask)); queue_stop_cpus_work(cpumask, fn, arg, &done, false); - wait_for_stop_done(&done); + wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT; } @@ -326,13 +308,7 @@ repeat: kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL, ksym_buf), arg); - /* - * Make sure that the wakeup and setting done->waiter - * to NULL is atomic. - */ - local_irq_disable(); cpu_stop_signal_done(done, true); - local_irq_enable(); goto repeat; } } @@ -573,7 +549,7 @@ int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data, ret = stop_machine_cpu_stop(&smdata); /* Busy wait for completion. */ - while (atomic_read(&done.nr_todo)) + while (!completion_done(&done.completion)) cpu_relax(); mutex_unlock(&stop_cpus_mutex); -- 2.7.0