From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752072AbcBLXDl (ORCPT ); Fri, 12 Feb 2016 18:03:41 -0500 Received: from www.linutronix.de ([62.245.132.108]:43530 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751888AbcBLXDF (ORCPT ); Fri, 12 Feb 2016 18:03:05 -0500 From: Sebastian Andrzej Siewior To: linux-rt-users@vger.kernel.org Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, Steven Rostedt , Sebastian Andrzej Siewior Subject: [PATCH RT 5/6] kernel/stop_machine: partly revert "stop_machine: Use raw spinlocks" Date: Sat, 13 Feb 2016 00:02:47 +0100 Message-Id: <1455318168-7125-5-git-send-email-bigeasy@linutronix.de> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1455318168-7125-1-git-send-email-bigeasy@linutronix.de> References: <1455318168-7125-1-git-send-email-bigeasy@linutronix.de> X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- kernel/stop_machine.c | 40 ++++++++-------------------------------- 1 file changed, 8 insertions(+), 32 deletions(-) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 2c5acc882bad..f84d3b45cda7 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -30,7 +30,7 @@ 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 */ @@ -59,7 +59,7 @@ 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 */ @@ -68,10 +68,8 @@ 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); } } @@ -96,22 +94,6 @@ 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 @@ -143,7 +125,7 @@ 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; } @@ -302,7 +284,7 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void * preempt_enable_nort(); - wait_for_stop_done(&done); + wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT; } @@ -364,7 +346,7 @@ 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; } @@ -495,13 +477,7 @@ static void cpu_stopper_thread(unsigned int cpu) 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; } } @@ -663,7 +639,7 @@ int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data, ret = multi_cpu_stop(&msdata); /* 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