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SubjectRe: bisected: 'perf top' causing soft lockups under Xen
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Re-send, with patch pasted in-line, rather than attached...


Hmm - sorry I neglected this - it got filtered into my LKML folder,
which I usually ignore, unless I'm looking for something.
I'll have to adjust that filter for when I'm in the To: line.

I've attached a work-in-progress patch, that allows for kdb to work
with the hvc console.

It assigns some IPI functions that may be applicable here...

That said - I'm not convinced it "rounds up" the cpus
properly...though I haven't been able to prove otherwise. It seems to
work generally...



diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index d5e0e0a..88815a1 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -65,6 +65,7 @@

#include "xen-ops.h"
#include "mmu.h"
+#include "smp.h"
#include "multicalls.h"

EXPORT_SYMBOL_GPL(hypercall_page);
@@ -768,6 +769,12 @@ static void set_xen_basic_apic_ops(void)
apic->icr_write = xen_apic_icr_write;
apic->wait_icr_idle = xen_apic_wait_icr_idle;
apic->safe_wait_icr_idle = xen_safe_apic_wait_icr_idle;
+
+ apic->send_IPI_allbutself = xen_send_IPI_allbutself;
+ apic->send_IPI_mask_allbutself = xen_send_IPI_mask_allbutself;
+ apic->send_IPI_mask = xen_send_IPI_mask;
+ apic->send_IPI_all = xen_send_IPI_all;
+ apic->send_IPI_self = xen_send_IPI_self;
}

#endif
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 3061244..d8928a1 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -436,8 +436,8 @@ static void xen_smp_send_reschedule(int cpu)
xen_send_IPI_one(cpu, XEN_RESCHEDULE_VECTOR);
}

-static void xen_send_IPI_mask(const struct cpumask *mask,
- enum ipi_vector vector)
+void xen_send_IPI_mask(const struct cpumask *mask,
+ int vector)
{
unsigned cpu;

@@ -466,6 +466,39 @@ static void xen_smp_send_call_function_single_ipi(int cpu)
XEN_CALL_FUNCTION_SINGLE_VECTOR);
}

+void xen_send_IPI_all(int vector)
+{
+ xen_send_IPI_mask(cpu_online_mask, vector);
+}
+
+void xen_send_IPI_self(int vector)
+{
+ xen_send_IPI_one(smp_processor_id(), vector);
+}
+
+void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
+ int vector)
+{
+ unsigned cpu;
+ unsigned int this_cpu = smp_processor_id();
+
+ if (!(num_online_cpus() > 1))
+ return;
+
+ for_each_cpu_and(cpu, mask, cpu_online_mask) {
+ if (this_cpu == cpu)
+ continue;
+
+ xen_smp_send_call_function_single_ipi(cpu);
+ }
+}
+
+void xen_send_IPI_allbutself(int vector)
+{
+ xen_send_IPI_mask_allbutself(cpu_online_mask, vector);
+}
+
+
static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)
{
irq_enter();
diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h
new file mode 100644
index 0000000..8981a76
--- /dev/null
+++ b/arch/x86/xen/smp.h
@@ -0,0 +1,12 @@
+#ifndef _XEN_SMP_H
+
+extern void xen_send_IPI_mask(const struct cpumask *mask,
+ int vector);
+extern void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
+ int vector);
+extern void xen_send_IPI_allbutself(int vector);
+extern void physflat_send_IPI_allbutself(int vector);
+extern void xen_send_IPI_all(int vector);
+extern void xen_send_IPI_self(int vector);
+
+#endif
diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 58ca7ce..4addc80 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -754,13 +754,10 @@ int hvc_poll_init(struct tty_driver *driver, int
line, char *options)

static int hvc_poll_get_char(struct tty_driver *driver, int line)
{
- struct tty_struct *tty = driver->ttys[0];
- struct hvc_struct *hp = tty->driver_data;
int n;
char ch;

- n = hp->ops->get_chars(hp->vtermno, &ch, 1);
-
+ n = cons_ops[last_hvc]->get_chars(vtermnos[last_hvc], &ch, 1);
if (n == 0)
return NO_POLL_CHAR;

@@ -769,12 +766,10 @@ static int hvc_poll_get_char(struct tty_driver
*driver, int line)

static void hvc_poll_put_char(struct tty_driver *driver, int line, char ch)
{
- struct tty_struct *tty = driver->ttys[0];
- struct hvc_struct *hp = tty->driver_data;
int n;

do {
- n = hp->ops->put_chars(hp->vtermno, &ch, 1);
+ n = cons_ops[last_hvc]->put_chars(vtermnos[last_hvc], &ch, 1);
} while (n <= 0);
}
#endif
diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index cefd4a1..df904a5 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -581,12 +581,14 @@ return_normal:
kgdb_roundup_cpus(flags);
#endif

+#ifndef CONFIG_XEN
/*
* Wait for the other CPUs to be notified and be waiting for us:
*/
while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
atomic_read(&slaves_in_kgdb)) != online_cpus)
cpu_relax();
+#endif

/*
* At this point the primary processor is completely


On Fri, Feb 10, 2012 at 2:04 PM, Konrad Rzeszutek Wilk
<konrad.wilk@oracle.com> wrote:
>
> On Fri, Feb 10, 2012 at 06:28:21PM +0100, Peter Zijlstra wrote:
> > On Thu, 2012-02-09 at 18:32 -0800, Steven Noonan wrote:
> > > [   88.517599]  [<ffffffff81085a86>] smp_call_function_single+0xec/0xfd
> >
> > This looks like its waiting for an IPI to complete..
>
> Hmm, Ben you tried some kdb debugging using Xen and ran in some IPI issues
> didn't you? Do you remember what was the problem?
>
> >
> > There's no actual BUGS or WARNs in the output, just the soft lockup
> > thing saying things are taking a bit of time (clearly 15s waiting for an
> > IPI isn't quite normal).
> >
> > I've no idea why this wouldn't work on Xen, nor do the trace have any
> > Xen specific muck in them.
>
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