[PATCH 02/24] alpha: enter hardirq context before looking up the irq descriptor

[Matt Turner <mattst88@gmail.com>]

handle_irq() called irq_to_desc() before irq_enter(), so that lookup ran
with the preempt count still saying task context and with RCU not yet
watching.  Generic code called from an interrupt handler should see
hardirq context, and irq_to_desc() is more than an array index once
SPARSE_IRQ is in use.

Move irq_enter() to the top of the function and add the matching
irq_exit() to the invalid interrupt path.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 arch/alpha/kernel/irq.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git ./arch/alpha/kernel/irq.c ./arch/alpha/kernel/irq.c
index 4a6a8b1d5a8b..5867a1655045 100644
--- ./arch/alpha/kernel/irq.c
+++ ./arch/alpha/kernel/irq.c
@@ -107,18 +107,21 @@ handle_irq(int irq)
 	 * handled by some other CPU. (or is disabled)
 	 */
 	static unsigned int illegal_count=0;
-	struct irq_desc *desc = irq_to_desc(irq);
-	
+	struct irq_desc *desc;
+
+	irq_enter();
+
+	desc = irq_to_desc(irq);
 	if (!desc || ((unsigned) irq > ACTUAL_NR_IRQS &&
 	    illegal_count < MAX_ILLEGAL_IRQS)) {
 		irq_err_count++;
 		illegal_count++;
 		printk(KERN_CRIT "device_interrupt: invalid interrupt %d\n",
 		       irq);
+		irq_exit();
 		return;
 	}
 
-	irq_enter();
 	generic_handle_irq_desc(desc);
 	irq_exit();
 }
-- 
2.54.0