linux-kernel - [tip: x86/cache] x86/resctrl: Remove lockdep annotation that triggers false positive

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Date: Thu, 22 Feb 2024 15:26:19 -0000
From: "tip-bot2 for James Morse" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Tony Luck <tony.luck@...el.com>, James Morse <james.morse@....com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/cache] x86/resctrl: Remove lockdep annotation that triggers
 false positive

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     c0d848fcb09d80a5f48b99f85e448185125ef59f
Gitweb:        https://git.kernel.org/tip/c0d848fcb09d80a5f48b99f85e448185125ef59f
Author:        James Morse <james.morse@....com>
AuthorDate:    Wed, 21 Feb 2024 12:23:06 
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Thu, 22 Feb 2024 16:15:38 +01:00

x86/resctrl: Remove lockdep annotation that triggers false positive

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.

  [ bp: Refresh it ontop of x86/cache. ]

Fixes: fb700810d30b ("x86/resctrl: Separate arch and fs resctrl locks")
Reported-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: James Morse <james.morse@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Link: https://lore.kernel.org/all/ZdUSwOM9UUNpw84Y@agluck-desk3
---
 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 8a4ef4f..83e4034 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_HOTPLUG_CPU) && IS_ENABLED(CONFIG_LOCKDEP))
-		WARN_ON_ONCE(!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))