linux-kernel - [PATCH] x86/apic/vector: Fix ordering in vector assignment

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Message-ID: <87ft4djtyp.fsf@nanos.tec.linutronix.de>
Date:   Thu, 10 Dec 2020 21:18:22 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Shung-Hsi Yu <shung-hsi.yu@...e.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Ming Lei <ming.lei@...hat.com>, Peter Xu <peterx@...hat.com>
Subject: [PATCH] x86/apic/vector: Fix ordering in vector assignment

Prarit reported that depending on the affinity setting the

 ' irq $N: Affinity broken due to vector space exhaustion.'

message is showing up in dmesg, but the vector space on the CPUs in the
affinity mask is definitely not exhausted.

Shung-Hsi provided traces and analysis which pinpoints the problem:

The ordering of trying to assign an interrupt vector in
assign_irq_vector_any_locked() is simply wrong if the interrupt data has a
valid node assigned. It does:

 1) Try the intersection of affinity mask and node mask
 2) Try the node mask
 3) Try the full affinity mask
 4) Try the full online mask

Obviously #2 and #3 are in the wrong order as the requested affinity
mask has to take precedence.

In the observed cases #1 failed because the affinity mask did not contain
CPUs from node 0. That made it allocate a vector from node 0, thereby
breaking affinity and emitting the misleading message.

Revert the order of #2 and #3 so the full affinity mask without the node
intersection is tried before actually affinity is broken.

If no node is assigned then only the full affinity mask and if that fails
the full online mask is tried.

Fixes: d6ffc6ac83b1 ("x86/vector: Respect affinity mask in irq descriptor")
Reported-by: Shung-Hsi Yu <shung-hsi.yu@...e.com>
Reported-by: Prarit Bhargava <prarit@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Shung-Hsi Yu <shung-hsi.yu@...e.com>
Cc: stable@...r.kernel.org
---
 arch/x86/kernel/apic/vector.c |   24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -273,20 +273,24 @@ static int assign_irq_vector_any_locked(
 	const struct cpumask *affmsk = irq_data_get_affinity_mask(irqd);
 	int node = irq_data_get_node(irqd);
 
-	if (node == NUMA_NO_NODE)
-		goto all;
-	/* Try the intersection of @affmsk and node mask */
-	cpumask_and(vector_searchmask, cpumask_of_node(node), affmsk);
-	if (!assign_vector_locked(irqd, vector_searchmask))
-		return 0;
-	/* Try the node mask */
-	if (!assign_vector_locked(irqd, cpumask_of_node(node)))
-		return 0;
-all:
+	if (node != NUMA_NO_NODE) {
+		/* Try the intersection of @affmsk and node mask */
+		cpumask_and(vector_searchmask, cpumask_of_node(node), affmsk);
+		if (!assign_vector_locked(irqd, vector_searchmask))
+			return 0;
+	}
+
 	/* Try the full affinity mask */
 	cpumask_and(vector_searchmask, affmsk, cpu_online_mask);
 	if (!assign_vector_locked(irqd, vector_searchmask))
 		return 0;
+
+	if (node != NUMA_NO_NODE) {
+		/* Try the node mask */
+		if (!assign_vector_locked(irqd, cpumask_of_node(node)))
+			return 0;
+	}
+
 	/* Try the full online mask */
 	return assign_vector_locked(irqd, cpu_online_mask);
 }