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Re: [PATCH v2] x86/apic: Avoid infinite loop in io_apic_level_ack_pending()
- To: Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jason Andryuk <jason.andryuk@xxxxxxx>
- Date: Wed, 15 Oct 2025 13:14:20 -0400
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- Cc: <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Wed, 15 Oct 2025 17:14:39 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-10-15 08:59, Jan Beulich wrote:
On 14.10.2025 09:37, Roger Pau Monné wrote:
On Mon, Oct 13, 2025 at 05:11:06PM -0400, Jason Andryuk wrote:
io_apic_level_ack_pending() will end up in an infinite loop if
entry->pin == -1. entry does not change, so it will keep reading -1.
Do you know how you end up with an entry with pin == -1 on the
irq_pin_list? Are there systems with gaps in the GSI space between
IO-APICs? So far everything I saw had the IO-APIC in contiguous GSI
space.
Convert to a proper for loop so that continue works. Add a new helper,
next_entry(), to handle advancing to the next irq_pin_list entry.
Fixes: f821102450a1 ("x86: IRQ Migration logic enhancement.")
Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
---
v2:
continue (not break) for pin == -1.
I added the next_entry() helper since putting the expression in the for
loop is a little cluttered. The helper can also be re-used for other
instances within the file.
Would this intention ...
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -1586,14 +1586,21 @@ static int __init cf_check setup_ioapic_ack(const char
*s)
}
custom_param("ioapic_ack", setup_ioapic_ack);
+static struct irq_pin_list *next_entry(struct irq_pin_list *entry)
I think you can make the entry parameter const?
... possibly conflict with such a change?
I changed only the parameter to const, and the return value is still
non-const. So I think that will be re-usable.
I placed next_entry() immediately before its use in
io_apic_level_ack_pending(). It would need to be earlier in the file to
be used more. Should I move its addition earlier?
And another Minor question. Roger asked for ~Linux style in the for
loop. But in next_entry() I have Xen style:
if ( !entry->next )
Should I switch to:
if (!entry->next)
?
Thanks,
Jason
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