Re: system hung up when offlining CPUs
From: Thomas Gleixner
Date: Wed Oct 04 2017 - 17:04:54 EST
On Tue, 3 Oct 2017, Thomas Gleixner wrote:
> Can you please apply the debug patch below.
I found an issue with managed interrupts when the affinity mask of an
managed interrupt spawns multiple CPUs. Explanation in the changelog
below. I'm not sure that this cures the problems you have, but at least I
could prove that it's not doing what it should do. The failure I'm seing is
fixed, but I can't test that megasas driver due to -ENOHARDWARE.
Can you please apply the patch below on top of Linus tree and retest?
Please send me the outputs I asked you to provide last time in any case
(success or fail).
@block/scsi folks: Can you please run that through your tests as well?
Thanks,
tglx
8<-----------------------
Subject: genirq/cpuhotplug: Enforce affinity setting on startup of managed irqs
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Wed, 04 Oct 2017 21:07:38 +0200
Managed interrupts can end up in a stale state on CPU hotplug. If the
interrupt is not targeting a single CPU, i.e. the affinity mask spawns
multiple CPUs then the following can happen:
After boot:
dstate: 0x01601200
IRQD_ACTIVATED
IRQD_IRQ_STARTED
IRQD_SINGLE_TARGET
IRQD_AFFINITY_SET
IRQD_AFFINITY_MANAGED
node: 0
affinity: 24-31
effectiv: 24
pending: 0
After offlining CPU 31 - 24
dstate: 0x01a31000
IRQD_IRQ_DISABLED
IRQD_IRQ_MASKED
IRQD_SINGLE_TARGET
IRQD_AFFINITY_SET
IRQD_AFFINITY_MANAGED
IRQD_MANAGED_SHUTDOWN
node: 0
affinity: 24-31
effectiv: 24
pending: 0
Now CPU 25 gets onlined again, so it should get the effective interrupt
affinity for this interruopt, but due to the x86 interrupt affinity setter
restrictions this ends up after restarting the interrupt with:
dstate: 0x01601300
IRQD_ACTIVATED
IRQD_IRQ_STARTED
IRQD_SINGLE_TARGET
IRQD_AFFINITY_SET
IRQD_SETAFFINITY_PENDING
IRQD_AFFINITY_MANAGED
node: 0
affinity: 24-31
effectiv: 24
pending: 24-31
So the interrupt is still affine to CPU 24, which was the last CPU to go
offline of that affinity set and the move to an online CPU within 24-31,
in this case 25, is pending. This mechanism is x86/ia64 specific as those
architectures cannot move interrupts from thread context and do this when
an interrupt is actually handled. So the move is set to pending.
Whats worse is that offlining CPU 25 again results in:
dstate: 0x01601300
IRQD_ACTIVATED
IRQD_IRQ_STARTED
IRQD_SINGLE_TARGET
IRQD_AFFINITY_SET
IRQD_SETAFFINITY_PENDING
IRQD_AFFINITY_MANAGED
node: 0
affinity: 24-31
effectiv: 24
pending: 24-31
This means the interrupt has not been shut down, because the outgoing CPU
is not in the effective affinity mask, but of course nothing notices that
the effective affinity mask is pointing at an offline CPU.
In the case of restarting a managed interrupt the move restriction does not
apply, so the affinity setting can be made unconditional. This needs to be
done _before_ the interrupt is started up as otherwise the condition for
moving it from thread context would not longer be fulfilled.
With that change applied onlining CPU 25 after offlining 31-24 results in:
dstate: 0x01600200
IRQD_ACTIVATED
IRQD_IRQ_STARTED
IRQD_SINGLE_TARGET
IRQD_AFFINITY_MANAGED
node: 0
affinity: 24-31
effectiv: 25
pending:
And after offlining CPU 25:
dstate: 0x01a30000
IRQD_IRQ_DISABLED
IRQD_IRQ_MASKED
IRQD_SINGLE_TARGET
IRQD_AFFINITY_MANAGED
IRQD_MANAGED_SHUTDOWN
node: 0
affinity: 24-31
effectiv: 25
pending:
which is the correct and expected result.
To complete that, add some debug code to catch this kind of situation in
the cpu offline code and warn about interrupt chips which allow affinity
setting and do not update the effective affinity mask if that feature is
enabled.
Reported-by: YASUAKI ISHIMATSU <yasu.isimatu@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/irq/chip.c | 2 +-
kernel/irq/cpuhotplug.c | 28 +++++++++++++++++++++++++++-
kernel/irq/manage.c | 17 +++++++++++++++++
3 files changed, 45 insertions(+), 2 deletions(-)
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -265,8 +265,8 @@ int irq_startup(struct irq_desc *desc, b
irq_setup_affinity(desc);
break;
case IRQ_STARTUP_MANAGED:
+ irq_do_set_affinity(d, aff, false);
ret = __irq_startup(desc);
- irq_set_affinity_locked(d, aff, false);
break;
case IRQ_STARTUP_ABORT:
return 0;
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -18,8 +18,34 @@
static inline bool irq_needs_fixup(struct irq_data *d)
{
const struct cpumask *m = irq_data_get_effective_affinity_mask(d);
+ unsigned int cpu = smp_processor_id();
- return cpumask_test_cpu(smp_processor_id(), m);
+#ifdef CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK
+ /*
+ * The cpumask_empty() check is a workaround for interrupt chips,
+ * which do not implement effective affinity, but the architecture has
+ * enabled the config switch. Use the general affinity mask instead.
+ */
+ if (cpumask_empty(m))
+ m = irq_data_get_affinity_mask(d);
+
+ /*
+ * Sanity check. If the mask is not empty when excluding the outgoing
+ * CPU then it must contain at least one online CPU. The outgoing CPU
+ * has been removed from the online mask already.
+ */
+ if (cpumask_any_but(m, cpu) < nr_cpu_ids &&
+ cpumask_any_and(m, cpu_online_mask) >= nr_cpu_ids) {
+ /*
+ * If this happens then there was a missed IRQ fixup at some
+ * point. Warn about it and enforce fixup.
+ */
+ pr_warn("Eff. affinity %*pbl of IRQ %u contains only offline CPUs after offlining CPU %u\n",
+ cpumask_pr_args(m), d->irq, cpu);
+ return true;
+ }
+#endif
+ return cpumask_test_cpu(cpu, m);
}
static bool migrate_one_irq(struct irq_desc *desc)
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -168,6 +168,19 @@ void irq_set_thread_affinity(struct irq_
set_bit(IRQTF_AFFINITY, &action->thread_flags);
}
+static void irq_validate_effective_affinity(struct irq_data *data)
+{
+#ifdef CONFIG_GENERIC_IRQ_EFFECTIVE_AFF_MASK
+ const struct cpumask *m = irq_data_get_effective_affinity_mask(data);
+ struct irq_chip *chip = irq_data_get_irq_chip(data);
+
+ if (!cpumask_empty(m))
+ return;
+ pr_warn_once("irq_chip %s did not update eff. affinity mask of irq %u\n",
+ chip->name, data->irq);
+#endif
+}
+
int irq_do_set_affinity(struct irq_data *data, const struct cpumask *mask,
bool force)
{
@@ -175,12 +188,16 @@ int irq_do_set_affinity(struct irq_data
struct irq_chip *chip = irq_data_get_irq_chip(data);
int ret;
+ if (!chip || !chip->irq_set_affinity)
+ return -EINVAL;
+
ret = chip->irq_set_affinity(data, mask, force);
switch (ret) {
case IRQ_SET_MASK_OK:
case IRQ_SET_MASK_OK_DONE:
cpumask_copy(desc->irq_common_data.affinity, mask);
case IRQ_SET_MASK_OK_NOCOPY:
+ irq_validate_effective_affinity(data);
irq_set_thread_affinity(desc);
ret = 0;
}