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SubjectPATCH/RFC: [kdump] fix APIC shutdown sequence
PATCH/RFC: [kdump] fix APIC shutdown sequence

This patch fixes a problem that we have encountered
with kdump under high I/O load on some machines.
The machines showing the errors have an Intel ICH7
chip set with a 6702PXH PCI Express-to-PCI Bridge
(8086:032c) containing an IO-APIC.

The bug symptom is that certain controllers connected
to the 6702PXH bridge wouldn't receive any IRQs in the
kdump kernel. In the error case (which is about 20% of
all cases) the IRR bit of the IO-APIC pin for that
controller is always set after the start of the kdump
kernel, indicating an IRQ in progress. We haven't found
a way to recover from this situation when it has once
occured, except for a system reset.

The error is caused by IRQs arriving while the APIC
subsystem is deactivated in machine_crash_shutdown().

Apparently, the IO-APIC gets stuck if it sends an IRQ
message to a Local APIC and never receives an EOI for that
message. This can have several possible reasons:

1. If, under SMP, the IO-APIC logical destination field is
set by the IRQ balancing code to one of the "other"
CPUs (i.e. not the crashing_cpu), and an IRQ arrives
on the respective pin after that CPU has shut down
its local APIC (but before the IO-APIC pin is masked)
the IRQ message can't be delivered.

2. The crashing CPU itself disables its local APIC
before the IO-APIC, leaving a short time window
where the IOAPIC can receive IRQs, but not
deliver them.

3. An IRQ is received and delivered to a local APIC, but
no CPU ever executes the IRQ handler and therefore no
EOI is sent.

After a lot of failed attempts, i have come up with the
following patch, which fixes the problem.

The patch first masks all IO-Apic pins to avoid a sitation
where the IO-Apic can receive, but not deliver, the IRQs.
Moreover, it enables interrupts for a short period before
eventually starting the kdump kernel, so that EOIs can be
sent to the APICs as necessary.

Notes:
a) Simply calling disable_IO_APIC() early doesn't
work, probably because that also clears the IRQ vector
information, so that arriving EOI messages can't be
associated with pins by the IO-APIC.
b) We have tried patches that avoid re-enabling interrupts,
but so far without success. Re-enabling IRQs is of course
dangerous while dumping, and I'd rather find a way to avoid it.
c) There are indications that besides the EOI, it's also
necessary that the PCI IRQ pin is deasserted at least for
a short time. That usually requires that the driver IRQ
handler is called and tells the FW that the IRQ was received.
Whether or not this is a requirement hasn't been finally
clarified yet.
d) The problem is only seen with the IO-APIC in the 6702PXH
PCI bridge, which is the system's secondary IO-APIC. On the
system's main IO-APIC, we see other IRQs (timer etc) arrive
and never get an EOI, but we see no errors.

The patch below is against 2.6.23-rc1. The problem was
originally analyzed and the patch developed against the
Red Hat EL5 kernel (2.6.18-8.el5). I verified that the
problem still occurs with 2.6.23-rc1, and that the patch
below fixes the problem.

Regards
Martin

PS: patch attached ain MIME format because it'd be mangled
quoted-printable by my Mail relay.

--
Martin Wilck
PRIMERGY System Software Engineer
FSC IP ESP DE6

Fujitsu Siemens Computers GmbH
Heinz-Nixdorf-Ring 1
33106 Paderborn
Germany

Tel: ++49 5251 8 15113
Fax: ++49 5251 8 20409
Email: mailto:martin.wilck@fujitsu-siemens.com
Internet: http://www.fujitsu-siemens.com
Company Details: http://www.fujitsu-siemens.com/imprint.html

PATCH/RFC: [kdump] fix APIC shutdown sequence

This patch fixes a problem that we have encountered
with kdump under high I/O load on some machines.
The machines showing the errors have an Intel ICH7
chip set with a 6702PXH PCI Express-to-PCI Bridge
(8086:032c) containing an IO-APIC.

The bug symptom is that certain controllers connected
to the 6702PXH bridge wouldn't receive any IRQs in the
kdump kernel. In the error case (which is about 20% of
all cases) the IRR bit of the IO-APIC pin for that
controller is always set after the start of the kdump
kernel, indicating an IRQ in progress. We haven't found
a way to recover from this situation when it has once
occured, except for a system reset.

The error is caused by IRQs arriving while the APIC
subsystem is deactivated in machine_crash_shutdown().

Apparently, the IO-APIC gets stuck if it sends an IRQ
message to a Local APIC and never receives an EOI for that
message. This can have several possible reasons:

1. If, under SMP, the IO-APIC logical destination field is
set by the IRQ balancing code to one of the "other"
CPUs (i.e. not the crashing_cpu), and an IRQ arrives
on the respective pin after that CPU has shut down
its local APIC (but before the IO-APIC pin is masked)
the IRQ message can't be delivered.

2. The crashing CPU itself disables its local APIC
before the IO-APIC, leaving a short time window
where the IOAPIC can receive IRQs, but not
deliver them.

3. An IRQ is received and delivered to a local APIC, but
no CPU ever executes the IRQ handler and therefore no
EOI is sent.

After a lot of failed attempts, i have come up with the
following patch, which fixes the problem.

The patch first masks all IO-Apic pins to avoid a sitation
where the IO-Apic can receive, but not deliver, the IRQs.
Moreover, it enables interrupts for a short period before
eventually starting the kdump kernel, so that EOIs can be
sent to the APICs as necessary.

Notes:
a) Simply calling disable_IO_APIC() early doesn't
work, probably because that also clears the IRQ vector
information, so that arriving EOI messages can't be
associated with pins by the IO-APIC.
b) We have tried patches that avoid re-enabling interrupts,
but so far without success. Re-enabling IRQs is of course
dangerous while dumping, and I'd rather find a way to avoid it.
c) There are indications that besides the EOI, it's also
necessary that the PCI IRQ pin is deasserted at least for
a short time. That usually requires that the driver IRQ
handler is called and tells the FW that the IRQ was received.
Whether or not this is a requirement hasn't been finally
clarified yet.
d) The problem is only seen with the IO-APIC in the 6702PXH
PCI bridge, which is the system's secondary IO-APIC. On the
system's main IO-APIC, we see other IRQs (timer etc) arrive
and never get an EOI, but we see no errors.

The patch below is against 2.6.23-rc1. The problem was
originally analyzed and the patch developed against the
Red Hat EL5 kernel (2.6.18-8.el5). I verified that the
problem still occurs with 2.6.23-rc1, and that the patch
below fixes the problem.

Regards
Martin

Signed-off-by: Martin Wilck <Martin.Wilck@fujitsu-siemens.com>


--- 2.6.23-rc1/arch/x86_64/kernel/crash.c.orig 2007-06-05 11:19:07.000000000 +0200
+++ 2.6.23-rc1/arch/x86_64/kernel/crash.c 2007-08-02 12:38:05.000000000 +0200
@@ -18,6 +18,7 @@
#include <linux/elf.h>
#include <linux/elfcore.h>
#include <linux/kdebug.h>
+#include <linux/interrupt.h>

#include <asm/processor.h>
#include <asm/hardirq.h>
@@ -30,6 +31,11 @@ static int crashing_cpu;

#ifdef CONFIG_SMP
static atomic_t waiting_for_crash_ipi;
+static atomic_t crash_ipi_stage2 = ATOMIC_INIT(0);
+
+extern void remove_siblinginfo(int);
+extern void remove_cpu_from_maps(void);
+extern void crash_mask_IO_APIC(int);

static int crash_nmi_callback(struct notifier_block *self,
unsigned long val, void *data)
@@ -53,13 +59,30 @@ static int crash_nmi_callback(struct not
local_irq_disable();

crash_save_cpu(regs, cpu);
- disable_local_APIC();
- atomic_dec(&waiting_for_crash_ipi);
+ disable_APIC_timer();
+ atomic_dec(&waiting_for_crash_ipi);
+
+ while(atomic_read(&crash_ipi_stage2) == 0)
+ cpu_relax();
+
+ /* Send EOI for pending IRQs */
+ local_irq_enable();
+ udelay(10000);
+ local_irq_disable();
+
+ remove_siblinginfo(cpu);
+ cpu_clear(cpu, cpu_online_map);
+ remove_cpu_from_maps();
+
+ disable_local_APIC();
+ atomic_dec(&crash_ipi_stage2);
+
+
/* Assume hlt works */
for(;;)
halt();

- return 1;
+ return NOTIFY_OK;
}

static void smp_send_nmi_allbutself(void)
@@ -79,7 +102,7 @@ static struct notifier_block crash_nmi_n

static void nmi_shootdown_cpus(void)
{
- unsigned long msecs;
+ unsigned long usecs;

atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
if (register_die_notifier(&crash_nmi_nb))
@@ -93,19 +116,33 @@ static void nmi_shootdown_cpus(void)

smp_send_nmi_allbutself();

+ usecs = 1000000; /* Wait at most a second for the other cpus to stop */
+ while ((atomic_read(&waiting_for_crash_ipi) > 0) && usecs) {
+ udelay(1);
+ usecs--;
+ }
+}
+
+static void nmi_shootdown_cpus_stage2(void)
+{
+
+ unsigned long msecs;
+ atomic_set(&crash_ipi_stage2, num_online_cpus());
+
msecs = 1000; /* Wait at most a second for the other cpus to stop */
- while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
+ while ((atomic_read(&crash_ipi_stage2) > 1) && msecs) {
mdelay(1);
msecs--;
}
- /* Leave the nmi callback set */
- disable_local_APIC();
}
#else
static void nmi_shootdown_cpus(void)
{
/* There are no cpus to shootdown */
}
+static void nmi_shootdown_cpus_stage2(void)
+{
+}
#endif

void machine_crash_shutdown(struct pt_regs *regs)
@@ -121,15 +158,27 @@ void machine_crash_shutdown(struct pt_re
*/
/* The kernel is broken so disable interrupts */
local_irq_disable();
-
/* Make a note of crashing cpu. Will be used in NMI callback.*/
crashing_cpu = smp_processor_id();
+ crash_save_cpu(regs, crashing_cpu);
+
+ /* disable timer interrupts */
+ disable_irq_nosync(0);
+ disable_APIC_timer();
+
nmi_shootdown_cpus();

+ /* Mask all IRQs, and make sure they are delivered to this CPU */
+ crash_mask_IO_APIC(crashing_cpu);
+ nmi_shootdown_cpus_stage2();
+
if(cpu_has_apic)
disable_local_APIC();

+ /* Send EOI for pending IRQs */
+ local_irq_enable();
+ udelay(10000);
+ local_irq_disable();
+
disable_IO_APIC();
-
- crash_save_cpu(regs, smp_processor_id());
}
--- 2.6.23-rc1/arch/x86_64/kernel/io_apic.c.orig 2007-07-25 17:50:05.000000000 +0200
+++ 2.6.23-rc1/arch/x86_64/kernel/io_apic.c 2007-08-02 12:17:57.000000000 +0200
@@ -371,6 +371,50 @@ static void unmask_IO_APIC_irq (unsigned
spin_unlock_irqrestore(&ioapic_lock, flags);
}

+static void crash_mask_IO_APIC_pin(unsigned int apic, unsigned int pin, int reg1)
+{
+ struct IO_APIC_route_entry entry;
+ unsigned long flags;
+
+ /* Check delivery_mode to be sure we're not clearing an SMI pin
+ * Don't bother disabling masked pins
+ */
+ spin_lock_irqsave(&ioapic_lock, flags);
+ *(((int*)&entry) + 0) = io_apic_read(apic, 0x10 + 2 * pin);
+ spin_unlock_irqrestore(&ioapic_lock, flags);
+ if (entry.delivery_mode == dest_SMI || entry.mask)
+ return;
+
+ entry.mask = 1;
+ *(((int*)&entry) + 1) = reg1;
+
+ spin_lock_irqsave(&ioapic_lock, flags);
+ io_apic_write(apic, 0x10 + 2 * pin, *(((int *)&entry) + 0));
+ io_apic_write(apic, 0x11 + 2 * pin, *(((int *)&entry) + 1));
+ io_apic_sync(apic);
+ spin_unlock_irqrestore(&ioapic_lock, flags);
+}
+
+/*
+ * This function is used for kdump to mask all IO-APIC IRQs, and reset
+ * the destination apic ID.
+ */
+void crash_mask_IO_APIC(int cpu)
+{
+ int apic, pin;
+ int reg1;
+ cpumask_t mask;
+
+ cpus_clear(mask);
+ cpu_set(cpu, mask);
+ reg1 = SET_APIC_LOGICAL_ID(cpu_mask_to_apicid(mask));
+
+ for (apic = 0; apic < nr_ioapics; apic++) {
+ for (pin = 0; pin < nr_ioapic_registers[apic]; pin++)
+ crash_mask_IO_APIC_pin(apic, pin, reg1);
+ }
+}
+
static void clear_IO_APIC_pin(unsigned int apic, unsigned int pin)
{
struct IO_APIC_route_entry entry;
--- 2.6.23-rc1/arch/x86_64/kernel/smpboot.c.orig 2007-06-05 11:19:07.000000000 +0200
+++ 2.6.23-rc1/arch/x86_64/kernel/smpboot.c 2007-08-02 12:17:57.000000000 +0200
@@ -973,7 +973,7 @@ void __init smp_cpus_done(unsigned int m

#ifdef CONFIG_HOTPLUG_CPU

-static void remove_siblinginfo(int cpu)
+void remove_siblinginfo(int cpu)
{
int sibling;
struct cpuinfo_x86 *c = cpu_data;
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