In kexec_prepare_cpus cpu, the primary CPU IPIs the secondary CPUs to
kexec_smp_down(). kexec_smp_down() calls kexec_smp_wait() which sets
the hw_cpu_id() to -1. The primary does this while leaving IRQs on
which means the primary can take a timer interrupt which can lead to
the primary IPIing one of the secondary CPUs (say, for a scheduler
re-balance) but since the secondary CPU now has a hw_cpu_id = -1, we
IPI CPU -1... Kaboom!
We are hitting this case regularly on POWER7 machines.
Also, the secondaries are clearing out any pending IPIs before
guaranteeing that no more will be received.
This changes kexec_prepare_cpus() so that we turn off IRQs in the
primary CPU much earlier. It adds a paca flag to say that the
secondaries have entered the kexec_smp_down() IPI and turned off IRQs,
rather than overloading hw_cpu_id with -1.
It also ensures that all CPUs have their IRQs off before we clear out
any pending IPI requests (in kexec_cpu_down()) to ensure there are no
trailing IPIs left unacknowledged.
Signed-off-by: Michael Neuling <mi...@neuling.org>
---
arch/powerpc/include/asm/paca.h | 1 +
arch/powerpc/kernel/machine_kexec_64.c | 28 ++++++++++++++++++++--------
arch/powerpc/kernel/misc_64.S | 3 ---
3 files changed, 21 insertions(+), 11 deletions(-)
Index: linux-2.6-ozlabs/arch/powerpc/include/asm/paca.h
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/include/asm/paca.h
+++ linux-2.6-ozlabs/arch/powerpc/include/asm/paca.h
@@ -82,6 +82,7 @@ struct paca_struct {
s16 hw_cpu_id; /* Physical processor number */
u8 cpu_start; /* At startup, processor spins until */
/* this becomes non-zero. */
+ u8 kexec_irqs_off; /* set when kexec down has irqs off */
#ifdef CONFIG_PPC_STD_MMU_64
struct slb_shadow *slb_shadow_ptr;
Index: linux-2.6-ozlabs/arch/powerpc/kernel/machine_kexec_64.c
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/kernel/machine_kexec_64.c
+++ linux-2.6-ozlabs/arch/powerpc/kernel/machine_kexec_64.c
@@ -155,16 +155,23 @@ void kexec_copy_flush(struct kimage *ima
#ifdef CONFIG_SMP
-/* FIXME: we should schedule this function to be called on all cpus based
- * on calling the interrupts, but we would like to call it off irq level
- * so that the interrupt controller is clean.
- */
+static int kexec_all_irq_disabled = 0;
+
static void kexec_smp_down(void *arg)
{
+ local_irq_disable();
+ mb(); /* make sure our irqs are disabled before we say they are */
+ get_paca()->kexec_irqs_off = 1;
+ while(kexec_all_irq_disabled == 0)
+ cpu_relax();
+ mb(); /* make sure all irqs are disabled before this */
+ /*
+ * Now every CPU has IRQs off, we can clear out any pending
+ * IPIs and be sure that no more will come in after this.
+ */
if (ppc_md.kexec_cpu_down)
ppc_md.kexec_cpu_down(0, 1);
- local_irq_disable();
kexec_smp_wait();
/* NOTREACHED */
}
@@ -174,14 +181,17 @@ static void kexec_prepare_cpus(void)
int my_cpu, i, notified=-1;
smp_call_function(kexec_smp_down, NULL, /* wait */0);
+ local_irq_disable();
+ mb(); /* make sure IRQs are disabled before we say they are */
+ get_paca()->kexec_irqs_off = 1;
my_cpu = get_cpu();
- /* check the others cpus are now down (via paca hw cpu id == -1) */
+ /* check the others cpus are now down (via paca kexec_irqs_off == 1) */
for (i=0; i < NR_CPUS; i++) {
if (i == my_cpu)
continue;
- while (paca[i].hw_cpu_id != -1) {
+ while (paca[i].kexec_irqs_off != 1) {
barrier();
if (!cpu_possible(i)) {
printk("kexec: cpu %d hw_cpu_id %d is not"
@@ -207,6 +217,9 @@ static void kexec_prepare_cpus(void)
}
}
}
+ mb();
+ /* we are sure every CPU has IRQs off at this point */
+ kexec_all_irq_disabled = 1;
/* after we tell the others to go down */
if (ppc_md.kexec_cpu_down)
@@ -214,7 +227,6 @@ static void kexec_prepare_cpus(void)
put_cpu();
- local_irq_disable();
}
#else /* ! SMP */
Index: linux-2.6-ozlabs/arch/powerpc/kernel/misc_64.S
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/kernel/misc_64.S
+++ linux-2.6-ozlabs/arch/powerpc/kernel/misc_64.S
@@ -494,14 +494,11 @@ kexec_flag:
* note: this is a terminal routine, it does not save lr
*
* get phys id from paca
- * set paca id to -1 to say we got here
* switch to real mode
* join other cpus in kexec_wait(phys_id)
*/
_GLOBAL(kexec_smp_wait)
lhz r3,PACAHWCPUID(r13)
- li r4,-1
- sth r4,PACAHWCPUID(r13) /* let others know we left */
bl real_mode
b .kexec_wait
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