Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756527AbcDBBjB (ORCPT ); Fri, 1 Apr 2016 21:39:01 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:53871 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756243AbcDBAy4 (ORCPT ); Fri, 1 Apr 2016 20:54:56 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: "Paul E . McKenney" , Andrew Morton , Linus Torvalds , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Owen Hofmann , Luis Henriques , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 018/170] cpu: Defer smpboot kthread unparking until CPU known to scheduler Date: Fri, 1 Apr 2016 17:51:44 -0700 Message-Id: <1459558456-24452-19-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1459558456-24452-1-git-send-email-kamal@canonical.com> References: <1459558456-24452-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3821 Lines: 125 3.19.8-ckt18 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: "Paul E. McKenney" commit 00df35f991914db6b8bde8cf09808e19a9cffc3d upstream. Currently, smpboot_unpark_threads() is invoked before the incoming CPU has been added to the scheduler's runqueue structures. This might potentially cause the unparked kthread to run on the wrong CPU, since the correct CPU isn't fully set up yet. That causes a sporadic, hard to debug boot crash triggering on some systems, reported by Borislav Petkov, and bisected down to: 2a442c9c6453 ("x86: Use common outgoing-CPU-notification code") This patch places smpboot_unpark_threads() in a CPU hotplug notifier with priority set so that these kthreads are unparked just after the CPU has been added to the runqueues. Reported-and-tested-by: Borislav Petkov Signed-off-by: Paul E. McKenney Cc: Andrew Morton Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar Cc: Owen Hofmann Signed-off-by: Luis Henriques Signed-off-by: Kamal Mostafa --- include/linux/cpu.h | 2 ++ init/main.c | 1 + kernel/cpu.c | 34 +++++++++++++++++++++++++++++++--- 3 files changed, 34 insertions(+), 3 deletions(-) diff --git a/include/linux/cpu.h b/include/linux/cpu.h index 4260e85..f1b8f4a 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -73,6 +73,7 @@ enum { /* migration should happen before other stuff but after perf */ CPU_PRI_PERF = 20, CPU_PRI_MIGRATION = 10, + CPU_PRI_SMPBOOT = 9, /* bring up workqueues before normal notifiers and down after */ CPU_PRI_WORKQUEUE_UP = 5, CPU_PRI_WORKQUEUE_DOWN = -5, @@ -161,6 +162,7 @@ static inline void __unregister_cpu_notifier(struct notifier_block *nb) } #endif +void smpboot_thread_init(void); int cpu_up(unsigned int cpu); void notify_cpu_starting(unsigned int cpu); extern void cpu_maps_update_begin(void); diff --git a/init/main.c b/init/main.c index 4872fb5..94138aa 100644 --- a/init/main.c +++ b/init/main.c @@ -397,6 +397,7 @@ static noinline void __init_refok rest_init(void) int pid; rcu_scheduler_starting(); + smpboot_thread_init(); /* * We need to spawn init first so that it obtains pid 1, however * the init task will end up wanting to create kthreads, which, if diff --git a/kernel/cpu.c b/kernel/cpu.c index 1972b16..ebfb188 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -446,6 +446,37 @@ out: EXPORT_SYMBOL(cpu_down); #endif /*CONFIG_HOTPLUG_CPU*/ +/* + * Unpark per-CPU smpboot kthreads at CPU-online time. + */ +static int smpboot_thread_call(struct notifier_block *nfb, + unsigned long action, void *hcpu) +{ + int cpu = (long)hcpu; + + switch (action & ~CPU_TASKS_FROZEN) { + + case CPU_ONLINE: + smpboot_unpark_threads(cpu); + break; + + default: + break; + } + + return NOTIFY_OK; +} + +static struct notifier_block smpboot_thread_notifier = { + .notifier_call = smpboot_thread_call, + .priority = CPU_PRI_SMPBOOT, +}; + +void __cpuinit smpboot_thread_init(void) +{ + register_cpu_notifier(&smpboot_thread_notifier); +} + /* Requires cpu_add_remove_lock to be held */ static int _cpu_up(unsigned int cpu, int tasks_frozen) { @@ -485,9 +516,6 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen) goto out_notify; BUG_ON(!cpu_online(cpu)); - /* Wake the per cpu threads */ - smpboot_unpark_threads(cpu); - /* Now call notifier in preparation. */ cpu_notify(CPU_ONLINE | mod, hcpu); -- 2.7.4