linux-kernel - [PATCH] genirq: Ensure flags in lock guard is consistently initialized

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Message-Id: <20250513-irq-guards-fix-flags-init-v1-1-1dca3f5992d6@kernel.org>
Date: Tue, 13 May 2025 00:16:55 +0200
From: Nathan Chancellor <nathan@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>, 
 Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] genirq: Ensure flags in lock guard is consistently
 initialized

After the conversion to locking guards within the interrupt core code,
several builds with clang show the "Interrupts were enabled early"
WARN() in start_kernel() on boot.

In class_irqdesc_lock_constructor(), _t.flags is initialized via
__irq_get_desc_lock() within the _t initializer list. However, the C11
standard 6.7.9.23 states that the evaluation of the initialization list
expressions are indeterminately sequenced relative to one another,
meaning _t.flags could be initialized by __irq_get_desc_lock() then be
initialized to zero due to flags being absent from the initializer list.

To ensure _t.flags is consistently initialized, move the call to
__irq_get_desc_lock() and the assignment of its result to _t.lock out of
the designated initializer.

Fixes: 0f70a49f3fa3 ("genirq: Provide conditional lock guards")
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 kernel/irq/internals.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index bd2db6ebb98e..476a20fd9bfc 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -176,10 +176,10 @@ __DEFINE_UNLOCK_GUARD(irqdesc_lock, struct irq_desc,
 static inline class_irqdesc_lock_t class_irqdesc_lock_constructor(unsigned int irq, bool bus,
 								  unsigned int check)
 {
-	class_irqdesc_lock_t _t = {
-		.bus	= bus,
-		.lock	= __irq_get_desc_lock(irq, &_t.flags, bus, check),
-	};
+	class_irqdesc_lock_t _t = { .bus = bus, };
+
+	_t.lock = __irq_get_desc_lock(irq, &_t.flags, bus, check);
+
 	return _t;
 }

---
base-commit: c1ab449df871d6ce9189cb0a9efcd37d2ead10f0
change-id: 20250512-irq-guards-fix-flags-init-1243eabe3401

Best regards,
-- 
Nathan Chancellor <nathan@...nel.org>