[PATCH v5 0/4] x86: fix hang when AP bringup is too slow

[PATCH v5 0/4] x86: fix hang when AP bringup is too slow

[Igor Mammedov]

changes since v4:
 * merge "[PATCH v4 1/5] x86: fix list corruption on CPU hotplug"
   and "[PATCH v4 2/5] x86: fix memory corruption in acpi_unmap_lsapic()"
   together
 * "x86: initialize secondary CPU only if master CPU will wait for it:
    - add 10 seconds timeout description into commit message
    - add smp_mb() after clearing cpu_initialized_mask

changes since v3:
 * put simple bugfixes first
 * move common part of syncing with master CPU in cpu_init()
   for x32/64 variant into helper function
 * cpu_init(): WARN_ON if cpu_initialized_mask is set
 * fix panic on CPU unplug, caused by erroneous removing
   of "pr->dev = dev;" in drivers/acpi/acpi_processor.c

--
Hang is observed on virtual machines during CPU hotplug,
especially in big guests with many CPUs. (It happens more
often if host is over-committed).

Hang happens because master CPU timeouts on waiting till
AP boots and 'cancels' CPU online operation assuming AP
is not functional but AP may continue run wild later
causing various hangs or panics in running kernel that
is assuming that AP was offline.

This is an alternative approach, that instead of canceling
in-progress AP bringup (https://lkml.org/lkml/2014/3/6/257),
removes timeouts so that AP bringup won't be affected by
poor timing and syncs AP with master CPU at early startup
making sure that AP won't run wild if master CPU doesn't
expect AP to come online.

Series also fixes 3 bugs found during testing CPU bringup
failure case.

--
Below is the detailed description of a more often happening hang:
---
Master CPU may timeout before cpu_callin_mask is set and cancel
booting CPU, but being onlined CPU still continues to boot, sets
cpu_active_mask (CPU_STARTING notifiers) and spins in
check_tsc_sync_target() for master cpu to arrive. Following attempt
to online another cpu hangs in stop_machine, initiated from here:
smp_callin ->
  smp_store_cpu_info ->
    identify_secondary_cpu ->
      mtrr_ap_init -> set_mtrr_from_inactive_cpu

stop_machine waits on completion of stop_work on all CPUs from
cpu_active_mask including a failed CPU that spins in check_tsc_sync_target().

Igor Mammedov (4):
  x86: fix list/memory corruption on CPU hotplug
  acpi_processor: do not mark present at boot but not onlined CPU as
    onlined
  x86: log error on secondary CPU wakeup failure at ERR level
  x86: initialize secondary CPU only if master CPU will wait for it

 arch/x86/kernel/cpu/common.c  |   27 ++++++----
 arch/x86/kernel/smpboot.c     |  104 +++++++++++++----------------------------
 drivers/acpi/acpi_processor.c |    1 -
 3 files changed, 48 insertions(+), 84 deletions(-)

[PATCH v5 1/4] x86: fix list/memory corruption on CPU hotplug

[Igor Mammedov]

currently if AP wake up is failed, master CPU marks AP as not present
in do_boot_cpu() by calling set_cpu_present(cpu, false).
That leads to following list corruption on the next physical CPU
hotplug:

[  418.107336] WARNING: CPU: 1 PID: 45 at lib/list_debug.c:33 __list_add+0xbe/0xd0()
[  418.115268] list_add corruption. prev->next should be next (ffff88003dc57600), but was ffff88003e20c3a0. (prev=ffff88003e20c3a0).
[  418.123693] Modules linked in: nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6t_REJECT ipt_REJECT cfg80211 xt_conntrack rfkill ee
[  418.138979] CPU: 1 PID: 45 Comm: kworker/u10:1 Not tainted 3.14.0-rc6+ #387
[  418.149989] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2007
[  418.165750] Workqueue: kacpi_hotplug acpi_hotplug_work_fn
[  418.166433]  0000000000000021 ffff880038ca7988 ffffffff8159b22d 0000000000000021
[  418.176460]  ffff880038ca79d8 ffff880038ca79c8 ffffffff8106942c ffff880038ca79e8
[  418.177453]  ffff88003e20c3a0 ffff88003dc57600 ffff88003e20c3a0 00000000ffffffea
[  418.178445] Call Trace:
[  418.185811]  [<ffffffff8159b22d>] dump_stack+0x49/0x5c
[  418.186440]  [<ffffffff8106942c>] warn_slowpath_common+0x8c/0xc0
[  418.187192]  [<ffffffff81069516>] warn_slowpath_fmt+0x46/0x50
[  418.191231]  [<ffffffff8136ef51>] ? acpi_ns_get_node+0xb7/0xc7
[  418.193889]  [<ffffffff812f796e>] __list_add+0xbe/0xd0
[  418.196649]  [<ffffffff812e2aa9>] kobject_add_internal+0x79/0x200
[  418.208610]  [<ffffffff812e2e18>] kobject_add_varg+0x38/0x60
[  418.213831]  [<ffffffff812e2ef4>] kobject_add+0x44/0x70
[  418.229961]  [<ffffffff813e2c60>] device_add+0xd0/0x550
[  418.234991]  [<ffffffff813f0e95>] ? pm_runtime_init+0xe5/0xf0
[  418.250226]  [<ffffffff813e32be>] device_register+0x1e/0x30
[  418.255296]  [<ffffffff813e82a3>] register_cpu+0xe3/0x130
[  418.266539]  [<ffffffff81592be5>] arch_register_cpu+0x65/0x150
[  418.285845]  [<ffffffff81355c0d>] acpi_processor_hotadd_init+0x5a/0x9b
...
Which is caused by the fact that generic_processor_info() allocates
logical CPU id by calling:

 cpu = cpumask_next_zero(-1, cpu_present_mask);

which returns id of previously failed to wake up CPU, since its bit
is cleared by do_boot_cpu() and as result register_cpu() tries to
register another CPU with the same id as already present but failed
to be onlined CPU.

Taking in account that AP will not do anything if master CPU failed to
wake it up, there is no reason to mark that AP as not present and
break next cpu hotplug attempts. As a side effect of not marking AP
as not present, user would be allowed to online it again later.

--
Also fix memory corruption in acpi_unmap_lsapic()

if during CPU hotplug master CPU failed to wake up AP
it set percpu x86_cpu_to_apicid to BAD_APICID=0xFFFF for AP.

However following attempt to unplug that CPU will lead to
out of bound write access to __apicid_to_node[] which is
32768 items long on x86_64 kernel.

So with above fix of cpu_present_mask make sure that a present
CPU has a valid APIC ID by not setting x86_cpu_to_apicid
to BAD_APICID in do_boot_cpu() on failure and allow
acpi_processor_remove()->acpi_unmap_lsapic() cleanly remove CPU.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
---
v2:
 - squash "[v4 2/5] x86: fix memory corruption in acpi_unmap_lsapic()"
   into "[v4 1/5]  x86: fix list corruption on CPU hotplug"
---
 arch/x86/kernel/smpboot.c |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 3482693..2988f69 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -859,9 +859,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 
 		/* was set by cpu_init() */
 		cpumask_clear_cpu(cpu, cpu_initialized_mask);
-
-		set_cpu_present(cpu, false);
-		per_cpu(x86_cpu_to_apicid, cpu) = BAD_APICID;
 	}
 
 	/* mark "stuck" area as not stuck */
-- 
1.7.1

[PATCH v5 2/4] acpi_processor: do not mark present at boot but not onlined CPU as onlined

[Igor Mammedov]

acpi_processor_add() assumes that present at boot CPUs
are always onlined, it is not so if a CPU failed to become
onlined. As result acpi_processor_add() will mark such CPU
device as onlined in sysfs and following attempts to
online/offline it using /sys/device/system/cpu/cpuX/online
attribute will fail.

Do not poke into device internals in acpi_processor_add()
and touch "struct device { .offline }" attribute, since
for CPUs onlined at boot it's set by:
  topology_init() -> arch_register_cpu() -> register_cpu()
before ACPI device tree is parsed, and for hotplugged
CPUs it's set when userspace onlines CPU via sysfs.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
---
v2:
 - fix regression in v1 leading to NULL pointer dereference
   on CPU unplug, do not remove "pr->dev = dev;"
---
 drivers/acpi/acpi_processor.c |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index b06f5f5..52c81c4 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -405,7 +405,6 @@ static int acpi_processor_add(struct acpi_device *device,
 		goto err;
 
 	pr->dev = dev;
-	dev->offline = pr->flags.need_hotplug_init;
 
 	/* Trigger the processor driver's .probe() if present. */
 	if (device_attach(dev) >= 0)
-- 
1.7.1

Re: [PATCH v5 2/4] acpi_processor: do not mark present at boot but not onlined CPU as onlined

[Rafael J. Wysocki]

On Monday, May 05, 2014 10:49:49 PM Igor Mammedov wrote:
> acpi_processor_add() assumes that present at boot CPUs
> are always onlined, it is not so if a CPU failed to become
> onlined. As result acpi_processor_add() will mark such CPU
> device as onlined in sysfs and following attempts to
> online/offline it using /sys/device/system/cpu/cpuX/online
> attribute will fail.
> 
> Do not poke into device internals in acpi_processor_add()
> and touch "struct device { .offline }" attribute, since
> for CPUs onlined at boot it's set by:
>   topology_init() -> arch_register_cpu() -> register_cpu()
> before ACPI device tree is parsed, and for hotplugged
> CPUs it's set when userspace onlines CPU via sysfs.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Acked-by: Toshi Kani <toshi.kani@hp.com>

Would there be a problem if I applied this separately from the rest of the
series?

> ---
> v2:
>  - fix regression in v1 leading to NULL pointer dereference
>    on CPU unplug, do not remove "pr->dev = dev;"
> ---
>  drivers/acpi/acpi_processor.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index b06f5f5..52c81c4 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -405,7 +405,6 @@ static int acpi_processor_add(struct acpi_device *device,
>  		goto err;
>  
>  	pr->dev = dev;
> -	dev->offline = pr->flags.need_hotplug_init;
>  
>  	/* Trigger the processor driver's .probe() if present. */
>  	if (device_attach(dev) >= 0)
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH v5 2/4] acpi_processor: do not mark present at boot but not onlined CPU as onlined

[Ingo Molnar]

* Rafael J. Wysocki <rjw@rjwysocki.net> wrote:

> On Monday, May 05, 2014 10:49:49 PM Igor Mammedov wrote:
> > acpi_processor_add() assumes that present at boot CPUs
> > are always onlined, it is not so if a CPU failed to become
> > onlined. As result acpi_processor_add() will mark such CPU
> > device as onlined in sysfs and following attempts to
> > online/offline it using /sys/device/system/cpu/cpuX/online
> > attribute will fail.
> > 
> > Do not poke into device internals in acpi_processor_add()
> > and touch "struct device { .offline }" attribute, since
> > for CPUs onlined at boot it's set by:
> >   topology_init() -> arch_register_cpu() -> register_cpu()
> > before ACPI device tree is parsed, and for hotplugged
> > CPUs it's set when userspace onlines CPU via sysfs.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > Acked-by: Toshi Kani <toshi.kani@hp.com>
> 
> Would there be a problem if I applied this separately from the rest 
> of the series?

If you push the fix upstream for v3.15 then it would be fine and I 
could base the other patches on top of your (soon to be upstream) 
commit.

Thanks,

	Ingo

Re: [PATCH v5 2/4] acpi_processor: do not mark present at boot but not onlined CPU as onlined

[Rafael J. Wysocki]

On Thursday, May 08, 2014 08:09:35 AM Ingo Molnar wrote:
> 
> * Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> 
> > On Monday, May 05, 2014 10:49:49 PM Igor Mammedov wrote:
> > > acpi_processor_add() assumes that present at boot CPUs
> > > are always onlined, it is not so if a CPU failed to become
> > > onlined. As result acpi_processor_add() will mark such CPU
> > > device as onlined in sysfs and following attempts to
> > > online/offline it using /sys/device/system/cpu/cpuX/online
> > > attribute will fail.
> > > 
> > > Do not poke into device internals in acpi_processor_add()
> > > and touch "struct device { .offline }" attribute, since
> > > for CPUs onlined at boot it's set by:
> > >   topology_init() -> arch_register_cpu() -> register_cpu()
> > > before ACPI device tree is parsed, and for hotplugged
> > > CPUs it's set when userspace onlines CPU via sysfs.
> > > 
> > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > > Acked-by: Toshi Kani <toshi.kani@hp.com>
> > 
> > Would there be a problem if I applied this separately from the rest 
> > of the series?
> 
> If you push the fix upstream for v3.15 then it would be fine and I 
> could base the other patches on top of your (soon to be upstream) 
> commit.

OK, I can do that.

We also seem to need this in -stable, right?


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

Re: [PATCH v5 2/4] acpi_processor: do not mark present at boot but not onlined CPU as onlined

[Ingo Molnar]

* Rafael J. Wysocki <rjw@rjwysocki.net> wrote:

> On Thursday, May 08, 2014 08:09:35 AM Ingo Molnar wrote:
> > 
> > * Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> > 
> > > On Monday, May 05, 2014 10:49:49 PM Igor Mammedov wrote:
> > > > acpi_processor_add() assumes that present at boot CPUs
> > > > are always onlined, it is not so if a CPU failed to become
> > > > onlined. As result acpi_processor_add() will mark such CPU
> > > > device as onlined in sysfs and following attempts to
> > > > online/offline it using /sys/device/system/cpu/cpuX/online
> > > > attribute will fail.
> > > > 
> > > > Do not poke into device internals in acpi_processor_add()
> > > > and touch "struct device { .offline }" attribute, since
> > > > for CPUs onlined at boot it's set by:
> > > >   topology_init() -> arch_register_cpu() -> register_cpu()
> > > > before ACPI device tree is parsed, and for hotplugged
> > > > CPUs it's set when userspace onlines CPU via sysfs.
> > > > 
> > > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > > > Acked-by: Toshi Kani <toshi.kani@hp.com>
> > > 
> > > Would there be a problem if I applied this separately from the rest 
> > > of the series?
> > 
> > If you push the fix upstream for v3.15 then it would be fine and I 
> > could base the other patches on top of your (soon to be upstream) 
> > commit.
> 
> OK, I can do that.
> 
> We also seem to need this in -stable, right?

Yeah, agreed.

Thanks,

	Ingo

[PATCH v5 3/4] x86: log error on secondary CPU wakeup failure at ERR level

[Igor Mammedov]

If system is running without debug level logging,
it will not log error if do_boot_cpu() failed to
wakeup AP. It may lead to silent AP bringup
failures at boot time.
Change message level to KERN_ERR to make error
visible to user as it's done on other architectures.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>
---
 arch/x86/kernel/smpboot.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 2988f69..ae2fd97 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -918,7 +918,7 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 
 	err = do_boot_cpu(apicid, cpu, tidle);
 	if (err) {
-		pr_debug("do_boot_cpu failed %d\n", err);
+		pr_err("do_boot_cpu failed(%d) to wakeup CPU#%u\n", err, cpu);
 		return -EIO;
 	}
 
-- 
1.7.1

[PATCH v5 4/4] x86: initialize secondary CPU only if master CPU will wait for it

[Igor Mammedov]

Hang is observed on virtual machines during CPU hotplug,
especially in big guests with many CPUs. (It reproducible
more often if host is over-committed).

It happens because master CPU gives up waiting on
secondary CPU and allows it to run wild. As result
AP causes locking or crashing system. For example
as described here: https://lkml.org/lkml/2014/3/6/257

If master CPU have sent STARTUP IPI successfully,
and AP signalled to master CPU that it's ready
to start initialization, make master CPU wait
indefinitely till AP is onlined.
To ensure that AP won't ever run wild, make it
wait at early startup till master CPU confirms its
intention to wait for AP. If AP doesn't respond in 10
seconds, the master CPU will timeout and cancel
AP onlining.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
v2:
 - ammend comment in cpu_init()
v3:
 - leave timeouts in do_boot_cpu(), so that master CPU
   won't hang if AP doesn't respond, use cpu_initialized_mask
   as a way for AP to signal to master CPU that it's ready
   to start initialzation.
v4:
 - move commont code in cpu_init() for x32/x64 in shared
   helper function wait_formaster_cpu()
 - add WARN_ON(cpumask_test_and_set_cpu(cpu, cpu_initialized_mask))
   to wait_formaster_cpu()
v5:
 - add smp_mb() after clearing cpu_initialized_mask in do_boot_cpu()
 - add 10 sec timeout description into commit message.
---
 arch/x86/kernel/cpu/common.c |   27 +++++++-----
 arch/x86/kernel/smpboot.c    |   99 +++++++++++++-----------------------------
 2 files changed, 47 insertions(+), 79 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a135239..a4bcbac 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1221,6 +1221,17 @@ static void dbg_restore_debug_regs(void)
 #define dbg_restore_debug_regs()
 #endif /* ! CONFIG_KGDB */
 
+static void wait_for_master_cpu(int cpu)
+{
+	/*
+	 * wait for ACK from master CPU before continuing
+	 * with AP initialization
+	 */
+	WARN_ON(cpumask_test_and_set_cpu(cpu, cpu_initialized_mask));
+	while (!cpumask_test_cpu(cpu, cpu_callout_mask))
+		cpu_relax();
+}
+
 /*
  * cpu_init() initializes state that is per-CPU. Some data is already
  * initialized (naturally) in the bootstrap process, such as the GDT
@@ -1236,16 +1247,17 @@ void cpu_init(void)
 	struct task_struct *me;
 	struct tss_struct *t;
 	unsigned long v;
-	int cpu;
+	int cpu = stack_smp_processor_id();
 	int i;
 
+	wait_for_master_cpu(cpu);
+
 	/*
 	 * Load microcode on this cpu if a valid microcode is available.
 	 * This is early microcode loading procedure.
 	 */
 	load_ucode_ap();
 
-	cpu = stack_smp_processor_id();
 	t = &per_cpu(init_tss, cpu);
 	oist = &per_cpu(orig_ist, cpu);
 
@@ -1257,9 +1269,6 @@ void cpu_init(void)
 
 	me = current;
 
-	if (cpumask_test_and_set_cpu(cpu, cpu_initialized_mask))
-		panic("CPU#%d already initialized!\n", cpu);
-
 	pr_debug("Initializing CPU#%d\n", cpu);
 
 	clear_in_cr4(X86_CR4_VME|X86_CR4_PVI|X86_CR4_TSD|X86_CR4_DE);
@@ -1336,13 +1345,9 @@ void cpu_init(void)
 	struct tss_struct *t = &per_cpu(init_tss, cpu);
 	struct thread_struct *thread = &curr->thread;
 
-	show_ucode_info_early();
+	wait_for_master_cpu(cpu);
 
-	if (cpumask_test_and_set_cpu(cpu, cpu_initialized_mask)) {
-		printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
-		for (;;)
-			local_irq_enable();
-	}
+	show_ucode_info_early();
 
 	printk(KERN_INFO "Initializing CPU#%d\n", cpu);
 
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ae2fd97..bc52fac 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -111,7 +111,6 @@ atomic_t init_deasserted;
 static void smp_callin(void)
 {
 	int cpuid, phys_id;
-	unsigned long timeout;
 
 	/*
 	 * If waken up by an INIT in an 82489DX configuration
@@ -130,37 +129,6 @@ static void smp_callin(void)
 	 * (This works even if the APIC is not enabled.)
 	 */
 	phys_id = read_apic_id();
-	if (cpumask_test_cpu(cpuid, cpu_callin_mask)) {
-		panic("%s: phys CPU#%d, CPU#%d already present??\n", __func__,
-					phys_id, cpuid);
-	}
-	pr_debug("CPU#%d (phys ID: %d) waiting for CALLOUT\n", cpuid, phys_id);
-
-	/*
-	 * STARTUP IPIs are fragile beasts as they might sometimes
-	 * trigger some glue motherboard logic. Complete APIC bus
-	 * silence for 1 second, this overestimates the time the
-	 * boot CPU is spending to send the up to 2 STARTUP IPIs
-	 * by a factor of two. This should be enough.
-	 */
-
-	/*
-	 * Waiting 2s total for startup (udelay is not yet working)
-	 */
-	timeout = jiffies + 2*HZ;
-	while (time_before(jiffies, timeout)) {
-		/*
-		 * Has the boot CPU finished it's STARTUP sequence?
-		 */
-		if (cpumask_test_cpu(cpuid, cpu_callout_mask))
-			break;
-		cpu_relax();
-	}
-
-	if (!time_before(jiffies, timeout)) {
-		panic("%s: CPU%d started up but did not get a callout!\n",
-		      __func__, cpuid);
-	}
 
 	/*
 	 * the boot CPU has finished the init stage and is spinning
@@ -750,8 +718,8 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 	unsigned long start_ip = real_mode_header->trampoline_start;
 
 	unsigned long boot_error = 0;
-	int timeout;
 	int cpu0_nmi_registered = 0;
+	unsigned long timeout;
 
 	/* Just in case we booted with a single CPU. */
 	alternatives_enable_smp();
@@ -799,6 +767,15 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 	}
 
 	/*
+	 * AP might wait on cpu_callout_mask in cpu_init() with
+	 * cpu_initialized_mask set if previous attempt to online
+	 * it timed-out. Clear cpu_initialized_mask so that after
+	 * INIT/SIPI it could start with a clean state.
+	 */
+	cpumask_clear_cpu(cpu, cpu_initialized_mask);
+	smp_mb();
+
+	/*
 	 * Wake up a CPU in difference cases:
 	 * - Use the method in the APIC driver if it's defined
 	 * Otherwise,
@@ -810,55 +787,41 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
 		boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
 						     &cpu0_nmi_registered);
 
+
 	if (!boot_error) {
 		/*
-		 * allow APs to start initializing.
+		 * Wait 10s total for a response from AP
 		 */
-		pr_debug("Before Callout %d\n", cpu);
-		cpumask_set_cpu(cpu, cpu_callout_mask);
-		pr_debug("After Callout %d\n", cpu);
+		boot_error = -1;
+		timeout = jiffies + 10*HZ;
+		while (time_before(jiffies, timeout)) {
+			if (cpumask_test_cpu(cpu, cpu_initialized_mask)) {
+				/*
+				 * Tell AP to proceed with initialization
+				 */
+				cpumask_set_cpu(cpu, cpu_callout_mask);
+				boot_error = 0;
+				break;
+			}
+			udelay(100);
+			schedule();
+		}
+	}
 
+	if (!boot_error) {
 		/*
-		 * Wait 5s total for a response
+		 * Wait till AP completes initial initialization
 		 */
-		for (timeout = 0; timeout < 50000; timeout++) {
-			if (cpumask_test_cpu(cpu, cpu_callin_mask))
-				break;	/* It has booted */
-			udelay(100);
+		while (!cpumask_test_cpu(cpu, cpu_callin_mask)) {
 			/*
 			 * Allow other tasks to run while we wait for the
 			 * AP to come online. This also gives a chance
 			 * for the MTRR work(triggered by the AP coming online)
 			 * to be completed in the stop machine context.
 			 */
+			udelay(100);
 			schedule();
 		}
-
-		if (cpumask_test_cpu(cpu, cpu_callin_mask)) {
-			print_cpu_msr(&cpu_data(cpu));
-			pr_debug("CPU%d: has booted.\n", cpu);
-		} else {
-			boot_error = 1;
-			if (*trampoline_status == 0xA5A5A5A5)
-				/* trampoline started but...? */
-				pr_err("CPU%d: Stuck ??\n", cpu);
-			else
-				/* trampoline code not run */
-				pr_err("CPU%d: Not responding\n", cpu);
-			if (apic->inquire_remote_apic)
-				apic->inquire_remote_apic(apicid);
-		}
-	}
-
-	if (boot_error) {
-		/* Try to put things back the way they were before ... */
-		numa_remove_cpu(cpu); /* was set by numa_add_cpu */
-
-		/* was set by do_boot_cpu() */
-		cpumask_clear_cpu(cpu, cpu_callout_mask);
-
-		/* was set by cpu_init() */
-		cpumask_clear_cpu(cpu, cpu_initialized_mask);
 	}
 
 	/* mark "stuck" area as not stuck */
-- 
1.7.1

Re: [PATCH v5 4/4] x86: initialize secondary CPU only if master CPU will wait for it

[Toshi Kani]

On Mon, 2014-05-05 at 22:49 +0200, Igor Mammedov wrote:
> Hang is observed on virtual machines during CPU hotplug,
> especially in big guests with many CPUs. (It reproducible
> more often if host is over-committed).
> 
> It happens because master CPU gives up waiting on
> secondary CPU and allows it to run wild. As result
> AP causes locking or crashing system. For example
> as described here: https://lkml.org/lkml/2014/3/6/257
> 
> If master CPU have sent STARTUP IPI successfully,
> and AP signalled to master CPU that it's ready
> to start initialization, make master CPU wait
> indefinitely till AP is onlined.
> To ensure that AP won't ever run wild, make it
> wait at early startup till master CPU confirms its
> intention to wait for AP. If AP doesn't respond in 10
> seconds, the master CPU will timeout and cancel
> AP onlining.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>

Thanks for the update.

Acked-by: Toshi Kani <toshi.kani@hp.com>

-Toshi

Re: [PATCH v5 0/4] x86: fix hang when AP bringup is too slow

[Igor Mammedov]

On Mon,  5 May 2014 22:49:47 +0200
Igor Mammedov <imammedo@redhat.com> wrote:

> changes since v4:
>  * merge "[PATCH v4 1/5] x86: fix list corruption on CPU hotplug"
>    and "[PATCH v4 2/5] x86: fix memory corruption in acpi_unmap_lsapic()"
>    together
>  * "x86: initialize secondary CPU only if master CPU will wait for it:
>     - add 10 seconds timeout description into commit message
>     - add smp_mb() after clearing cpu_initialized_mask
> 
> changes since v3:
>  * put simple bugfixes first
>  * move common part of syncing with master CPU in cpu_init()
>    for x32/64 variant into helper function
>  * cpu_init(): WARN_ON if cpu_initialized_mask is set
>  * fix panic on CPU unplug, caused by erroneous removing
>    of "pr->dev = dev;" in drivers/acpi/acpi_processor.c
> 
> --
> Hang is observed on virtual machines during CPU hotplug,
> especially in big guests with many CPUs. (It happens more
> often if host is over-committed).
> 
> Hang happens because master CPU timeouts on waiting till
> AP boots and 'cancels' CPU online operation assuming AP
> is not functional but AP may continue run wild later
> causing various hangs or panics in running kernel that
> is assuming that AP was offline.
> 
> This is an alternative approach, that instead of canceling
> in-progress AP bringup (https://lkml.org/lkml/2014/3/6/257),
> removes timeouts so that AP bringup won't be affected by
> poor timing and syncs AP with master CPU at early startup
> making sure that AP won't run wild if master CPU doesn't
> expect AP to come online.
> 
> Series also fixes 3 bugs found during testing CPU bringup
> failure case.

since 3.16 merge window is open now,
ping

> --
> Below is the detailed description of a more often happening hang:
> ---
> Master CPU may timeout before cpu_callin_mask is set and cancel
> booting CPU, but being onlined CPU still continues to boot, sets
> cpu_active_mask (CPU_STARTING notifiers) and spins in
> check_tsc_sync_target() for master cpu to arrive. Following attempt
> to online another cpu hangs in stop_machine, initiated from here:
> smp_callin ->
>   smp_store_cpu_info ->
>     identify_secondary_cpu ->
>       mtrr_ap_init -> set_mtrr_from_inactive_cpu
> 
> stop_machine waits on completion of stop_work on all CPUs from
> cpu_active_mask including a failed CPU that spins in check_tsc_sync_target().
> 
> Igor Mammedov (4):
>   x86: fix list/memory corruption on CPU hotplug
>   acpi_processor: do not mark present at boot but not onlined CPU as
>     onlined
>   x86: log error on secondary CPU wakeup failure at ERR level
>   x86: initialize secondary CPU only if master CPU will wait for it
> 
>  arch/x86/kernel/cpu/common.c  |   27 ++++++----
>  arch/x86/kernel/smpboot.c     |  104 +++++++++++++----------------------------
>  drivers/acpi/acpi_processor.c |    1 -
>  3 files changed, 48 insertions(+), 84 deletions(-)
> 

Re: [PATCH v5 0/4] x86: fix hang when AP bringup is too slow

[Ingo Molnar]

* Igor Mammedov <imammedo@redhat.com> wrote:

> > Series also fixes 3 bugs found during testing CPU bringup
> > failure case.
> 
> since 3.16 merge window is open now,
> ping

Mind resending the remaining patches on top of Linus's latest, which I 
suppose has one of the fixes already included via Rafael's tree?

Thanks,

	Ingo

Re: [PATCH v5 0/4] x86: fix hang when AP bringup is too slow

[Igor Mammedov]

On Thu, 5 Jun 2014 14:29:40 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Igor Mammedov <imammedo@redhat.com> wrote:
> 
> > > Series also fixes 3 bugs found during testing CPU bringup
> > > failure case.
> > 
> > since 3.16 merge window is open now,
> > ping
> 
> Mind resending the remaining patches on top of Linus's latest, which I 
> suppose has one of the fixes already included via Rafael's tree?
Sure, I'll rebase and repost it today.

> 
> Thanks,
> 
> 	Ingo