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From:   "H. Peter Anvin" <hpa@zytor.com>
To:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH v2.1 7/8] x86/irq: WARN_ONCE() if irq_move_cleanup is called on a pending interrupt
Date:   Sat, 15 May 2021 02:59:07 -0700
Message-Id: <20210515095907.3020486-1-hpa@zytor.com>
In-Reply-To: <20210515014400.2999028-8-hpa@zytor.com>
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From: "H. Peter Anvin (Intel)" <hpa@zytor.com>

The current IRQ vector allocation code should be "clean" and never
issue a IRQ_MOVE_CLEANUP_VECTOR IPI for an interrupt that could still
be pending. This should make it possible to move it to the "normal"
system IRQ vector range. This should probably be a three-step process:

1. Introduce this WARN_ONCE() on this event ever occurring.
2. Remove the self-IPI hack.
3. Move the IRQ_MOVE_CLEANUP_VECTOR to the sysvec range.

This implements step 1.

[ Previous versions of this patch had steps 2 and 3 reversed. ]

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
---
 arch/x86/kernel/apic/vector.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index 6dbdc7c22bb7..7ba2982a3585 100644
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -939,9 +939,14 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_irq_move_cleanup)
 		 * to this CPU. IRQ_MOVE_CLEANUP_VECTOR is the lowest
 		 * priority external vector, so on return from this
 		 * interrupt the device interrupt will happen first.
+		 *
+		 * *** This should never happen with the current IRQ
+		 * cleanup code, so WARN_ONCE() for now, and
+		 * eventually get rid of this hack.
 		 */
 		irr = apic_read(APIC_IRR + (vector / 32 * 0x10));
 		if (irr & (1U << (vector % 32))) {
+			WARN_ONCE(1, "irq_move_cleanup called on still pending interrupt\n");
 			apic->send_IPI_self(IRQ_MOVE_CLEANUP_VECTOR);
 			continue;
 		}
-- 
2.31.1