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From: James Morse <james.morse@arm.com>
To: x86@kernel.org,
	linux-kernel@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>,
	Reinette Chatre <reinette.chatre@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	H Peter Anvin <hpa@zytor.com>,
	Tony Luck <tony.luck@intel.com>,
	James Morse <james.morse@arm.com>
Subject: [PATCH] x86/resctrl: Remove lockdep annotation that triggers false positive
Date: Wed, 21 Feb 2024 12:23:06 +0000
Message-Id: <20240221122306.633273-1-james.morse@arm.com>
Precedence: bulk
MIME-Version: 1.0
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get_domain_from_cpu() walks a list of domains to find the one that
contains the specified CPU. This needs to be protected against races
with CPU hotplug when the list is modified. It has recently gained a
lockdep annotation to check this.

The lockdep annotation causes false positives when called via IPI
as the lock is held, but by another process. Remove it.

Reported-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/all/ZdUSwOM9UUNpw84Y@agluck-desk3/
Fixes: fb700810d30b ("x86/resctrl: Separate arch and fs resctrl locks")
Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/x86/kernel/cpu/resctrl/core.c | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 9f1aa555a8ea..83e40341583e 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -362,15 +362,6 @@ struct rdt_domain *get_domain_from_cpu(int cpu, struct rdt_resource *r)
 {
 	struct rdt_domain *d;
 
-	/*
-	 * Walking r->domains, ensure it can't race with cpuhp.
-	 * Because this is called via IPI by rdt_ctrl_update(), assertions
-	 * about locks this thread holds will lead to false positives. Check
-	 * someone is holding the CPUs lock.
-	 */
-	if (IS_ENABLED(CONFIG_LOCKDEP))
-		lockdep_is_cpus_held();
-
 	list_for_each_entry(d, &r->domains, list) {
 		/* Find the domain that contains this CPU */
 		if (cpumask_test_cpu(cpu, &d->cpu_mask))
-- 
2.39.2