Re: [PATCH 2/3] x86/irq: Use irq_chip_retrigger_hierarchy() in fixup_irqs()

[Naman Jain]

On 7/28/2026 7:33 PM, sashiko-...@kernel.org wrote:
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) 
to consider:
- [High] The patch replaces the direct invocation of the outermost chip's 
irq_retrigger() callback with irq_chip_retrigger_hierarchy(). However, 
irq_chip_retrigger_hierarchy() initializes its loop with `data = 
data->parent_data`, completely skipping the outermost chip. This breaks 
interrupt retriggering for flat domains (like native lapic_controller) and any 
hierarchical domain where the outermost chip directly implements the retrigger 
callback.
--

--- Patch [2]: [PATCH 2/3] x86/irq: Use irq_chip_retrigger_hierarchy() in 
fixup_irqs() ---
commit f97e883de2f6626561de48c426194caa41c3e062
Author: Naman Jain <namj...@linux.microsoft.com>
x86/irq: Use irq_chip_retrigger_hierarchy() in fixup_irqs()

This commit modifies fixup_irqs() to use irq_chip_retrigger_hierarchy()
instead of invoking the outermost domain chip's irq_retrigger() callback
directly. It also refactors the loop to use scoped guards for the irq
descriptor lock.

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 30122f0b3af96..ef1bdd3c4659a 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
[ ... ]
@@ -489,22 +484,18 @@ void fixup_irqs(void)
[ ... ]
-       for (vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; vector++) {
-               if (IS_ERR_OR_NULL(__this_cpu_read(vector_irq[vector])))
+       for (unsigned int vector = FIRST_EXTERNAL_VECTOR; vector < NR_VECTORS; 
vector++) {
+               struct irq_desc *desc = __this_cpu_read(vector_irq[vector]);
+
+               if (IS_ERR_OR_NULL(desc))
                        continue;
  
  		if (is_vector_pending(vector)) {
-                       desc = __this_cpu_read(vector_irq[vector]);
-
-                       raw_spin_lock(&desc->lock);
-                       data = irq_desc_get_irq_data(desc);
-                       chip = irq_data_get_irq_chip(data);
-                       if (chip->irq_retrigger) {
-                               chip->irq_retrigger(data);
+                       guard(raw_spinlock)(&desc->lock);
+                       if (irq_chip_retrigger_hierarchy(&desc->irq_data))
[Severity: High]
Will this skip the outermost chip and cause a regression for flat domains?

Looking at kernel/irq/chip.c:irq_chip_retrigger_hierarchy(), the loop
initializes by immediately moving to the parent_data:

     int irq_chip_retrigger_hierarchy(struct irq_data *data)
     {
         for (data = data->parent_data; data; data = data->parent_data)
             if (data->chip && data->chip->irq_retrigger)
                 return data->chip->irq_retrigger(data);

         return 0;
     }

By passing &desc->irq_data directly to this function, it seems any retrigger
callback on the outermost chip itself will be bypassed.

Could this lead to dropped hardware interrupts during CPU hot-unplug for
flat domains (like native lapic_controller) or any hierarchical domain where
the outermost chip implements the retrigger callback?

                                __this_cpu_write(vector_irq[vector], 
VECTOR_RETRIGGERED);
-                       }
-                       raw_spin_unlock(&desc->lock);
                }


I think this is a false positive, considering we are not changing the 
behavior for any of the existing chip->irq_retrigger(data) which come in 
this path (irq_chip_retrigger_hierarchy()).

Regards,
Naman