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SubjectRe: [PATCH] ioapic: fix potential resume deadlock
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On Tue, 2011-05-10 at 03:53 -0700, Daniel J Blueman wrote:
> On 10 May 2011 15:35, Ingo Molnar <mingo@elte.hu> wrote:
> > Hm, there must be some other bug here.
> >
> > ioapic entries should be allocated on system bootup and should never really be
> > deallocated.
> >
> > The bug might be in the idea to call to enable_IR_x2apic() on resume - why are
> > ioapic entries reallocated there? That call in default_setup_apic_routing() was
> > introduced some time ago in:
> >
> > fa47f7e52874: x86, x2apic: Simplify apic init in SMP and UP builds
> >
> > and that it results in reallocation in the suspend patch is distinctly wrong.
> >
> > I suspect the reason why this has not triggered for others is the relative
> > rarity of affected systems?
> >
> > Suresh?

This will happen only on interrupt-remapping enabled systems and hence
hidden so far.

enable_IR_x2apic() / default_setup_apic_routing() routines don't get
called during resume. Problem is with the lapic_resume() path which is
trying to re-enable x2apic mode and this requires masking io-apic
entries, re-enabling x2apic and interrupt-remapping, restoring io-apic
entries etc. ioapic entry allocation that is happening in lapic_resume()
is just for storing the original io-apic RTE's during the mask/restore
operations that happen around re-enabling x2apic.

Anyways looking at that code, there is some duplicate code between
x2apic code and the io-apic suspend/resume sequence. So a better fix
will be to remove this duplicate code.

Daniel, I appended a quick patch which should fix the problem you
reported. This is not a final patch, as I can do some more cleanup and
re-use the io-apic suspend/resume code a bit more.

If this patch works for you, then I can spend some more time to do the
complete cleanup patch in a day or two. Thanks.

arch/x86/include/asm/io_apic.h | 1 +
arch/x86/kernel/apic/apic.c | 26 ++++----------------------
arch/x86/kernel/apic/io_apic.c | 2 +-
3 files changed, 6 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/io_apic.h b/arch/x86/include/asm/io_apic.h
index a97a240..9e229be 100644
--- a/arch/x86/include/asm/io_apic.h
+++ b/arch/x86/include/asm/io_apic.h
@@ -177,6 +177,7 @@ extern void __init pre_init_apic_IRQ0(void);
extern void mp_save_irq(struct mpc_intsrc *m);

extern void disable_ioapic_support(void);
+extern struct IO_APIC_route_entry *ioapic_saved_data[MAX_IO_APICS];

#else /* !CONFIG_X86_IO_APIC */

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index fabf01e..9000409 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2088,28 +2088,14 @@ static void lapic_resume(void)
{
unsigned int l, h;
unsigned long flags;
- int maxlvt, ret;
- struct IO_APIC_route_entry **ioapic_entries = NULL;
+ int maxlvt;

if (!apic_pm_state.active)
return;

local_irq_save(flags);
if (intr_remapping_enabled) {
- ioapic_entries = alloc_ioapic_entries();
- if (!ioapic_entries) {
- WARN(1, "Alloc ioapic_entries in lapic resume failed.");
- goto restore;
- }
-
- ret = save_IO_APIC_setup(ioapic_entries);
- if (ret) {
- WARN(1, "Saving IO-APIC state failed: %d\n", ret);
- free_ioapic_entries(ioapic_entries);
- goto restore;
- }
-
- mask_IO_APIC_setup(ioapic_entries);
+ mask_IO_APIC_setup(ioapic_saved_data);
legacy_pic->mask_all();
}

@@ -2152,13 +2138,9 @@ static void lapic_resume(void)
apic_write(APIC_ESR, 0);
apic_read(APIC_ESR);

- if (intr_remapping_enabled) {
+ if (intr_remapping_enabled)
reenable_intr_remapping(x2apic_mode);
- legacy_pic->restore_mask();
- restore_IO_APIC_setup(ioapic_entries);
- free_ioapic_entries(ioapic_entries);
- }
-restore:
+
local_irq_restore(flags);
}

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 45fd33d..5e6a78e 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2918,7 +2918,7 @@ static int __init io_apic_bug_finalize(void)

late_initcall(io_apic_bug_finalize);

-static struct IO_APIC_route_entry *ioapic_saved_data[MAX_IO_APICS];
+struct IO_APIC_route_entry *ioapic_saved_data[MAX_IO_APICS];

static void suspend_ioapic(int ioapic_id)
{



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