From: Vivek Goyal <vgoyal@xxxxxxxxxx>
o check_timer() routine fails while second kernel is booting after a crash
on an opetron box. Problem happens because timer vector (0x31) seems to be
locked.
o After a system crash, it is not safe to service interrupts any more, hence
interrupts are disabled. This leads to pending interrupts at LAPIC. LAPIC
sends these interrupts to the CPU during early boot of second kernel. Other
pending interrupts are discarded saying unexpected trap but timer interrupt
is serviced and CPU does not issue an LAPIC EOI because it think this
interrupt came from i8259 and sends ack to 8259. This leads to vector 0x31
locking as LAPIC does not clear respective ISR and keeps on waiting for
EOI.
o This patch issues extra EOI for the pending interrupts who have ISR set.
o Though today only timer seems to be the special case because in early
boot it thinks interrupts are coming from i8259 and uses
mask_and_ack_8259A() as ack handler and does not issue LAPIC EOI. But
probably doing it in generic manner for all vectors makes sense.
Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxx>
---
---
arch/x86_64/kernel/apic.c | 20 ++++++++++++++++++++
include/asm-x86_64/apicdef.h | 1 +
2 files changed, 21 insertions(+)
Index: linux/arch/x86_64/kernel/apic.c
===================================================================
--- linux.orig/arch/x86_64/kernel/apic.c
+++ linux/arch/x86_64/kernel/apic.c
@@ -342,6 +342,7 @@ void __init init_bsp_APIC(void)
void __cpuinit setup_local_APIC (void)
{
unsigned int value, maxlvt;
+ int i, j;
value = apic_read(APIC_LVR);
@@ -371,6 +372,25 @@ void __cpuinit setup_local_APIC (void)
apic_write(APIC_TASKPRI, value);
/*
+ * After a crash, we no longer service the interrupts and a pending
+ * interrupt from previous kernel might still have ISR bit set.
+ *
+ * Most probably by now CPU has serviced that pending interrupt and
+ * it might not have done the ack_APIC_irq() because it thought,
+ * interrupt came from i8259 as ExtInt. LAPIC did not get EOI so it
+ * does not clear the ISR bit and cpu thinks it has already serivced
+ * the interrupt. Hence a vector might get locked. It was noticed
+ * for timer irq (vector 0x31). Issue an extra EOI to clear ISR.
+ */
+ for (i = APIC_ISR_NR - 1; i >= 0; i--) {
+ value = apic_read(APIC_ISR + i*0x10);
+ for (j = 31; j >= 0; j--) {
+ if (value & (1<<j))
+ ack_APIC_irq();
+ }
+ }
+
+ /*
* Now that we are all set up, enable the APIC
*/
value = apic_read(APIC_SPIV);
Index: linux/include/asm-x86_64/apicdef.h
===================================================================
--- linux.orig/include/asm-x86_64/apicdef.h
+++ linux/include/asm-x86_64/apicdef.h
@@ -39,6 +39,7 @@
#define APIC_SPIV_FOCUS_DISABLED (1<<9)
#define APIC_SPIV_APIC_ENABLED (1<<8)
#define APIC_ISR 0x100
+#define APIC_ISR_NR 0x8 /* Number of 32 bit ISR registers. */
#define APIC_TMR 0x180
#define APIC_IRR 0x200
#define APIC_ESR 0x280
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