From 528a25b00e1f84eaba6c98e63f58ee0a8e472102 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 28 Jan 2015 14:09:43 -0800 Subject: cpu: Make CPU-offline idle-loop transition point more precise This commit uses a per-CPU variable to make the CPU-offline code path through the idle loop more precise, so that the outgoing CPU is guaranteed to make it into the idle loop before it is powered off. This commit is in preparation for putting the RCU offline-handling code on this code path, which will eliminate the magic one-jiffy wait that RCU uses as the maximum time for an outgoing CPU to get all the way through the scheduler. The magic one-jiffy wait for incoming CPUs remains a separate issue. Signed-off-by: Paul E. McKenney --- kernel/cpu.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 1972b161c61e..d46b4dae0ca0 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -408,8 +408,10 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) * * Wait for the stop thread to go away. */ - while (!idle_cpu(cpu)) + while (!per_cpu(cpu_dead_idle, cpu)) cpu_relax(); + smp_mb(); /* Read from cpu_dead_idle before __cpu_die(). */ + per_cpu(cpu_dead_idle, cpu) = false; /* This actually kills the CPU. */ __cpu_die(cpu); -- cgit v1.2.3 From 00df35f991914db6b8bde8cf09808e19a9cffc3d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 12 Apr 2015 08:06:55 -0700 Subject: cpu: Defer smpboot kthread unparking until CPU known to scheduler 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 --- include/linux/cpu.h | 2 ++ init/main.c | 1 + kernel/cpu.c | 34 +++++++++++++++++++++++++++++++--- 3 files changed, 34 insertions(+), 3 deletions(-) (limited to 'kernel/cpu.c') diff --git a/include/linux/cpu.h b/include/linux/cpu.h index d028721748d4..091badf0f6ba 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, @@ -165,6 +166,7 @@ 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 6f0f1c5ff8cc..a12548c93318 100644 --- a/init/main.c +++ b/init/main.c @@ -384,6 +384,7 @@ 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 d46b4dae0ca0..57858cebd6b5 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -448,6 +448,37 @@ 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) { @@ -487,9 +518,6 @@ 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); -- cgit v1.2.3