linux-kernel - Re: [tip:timers/core] BUILD SUCCESS WITH UNVERIFIED WARNING 7dec062cfcf27808dbb70a0b231d1a698792743d

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Message-ID: <87v7j2hy3r.ffs@tglx>
Date: Sat, 22 Nov 2025 16:43:20 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: kernel test robot <lkp@...el.com>, x86-ml <x86@...nel.org>
Cc: linux-kernel@...r.kernel.org, Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [tip:timers/core] BUILD SUCCESS WITH UNVERIFIED WARNING
 7dec062cfcf27808dbb70a0b231d1a698792743d

On Sat, Nov 22 2025 at 15:20, kernel test robot wrote:

> tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/core
> branch HEAD: 7dec062cfcf27808dbb70a0b231d1a698792743d  timers/migration: Exclude isolated cpus from hierarchy
>
> Unverified Warning (likely false positive, kindly check if interested):
>
>     kernel/time/timer_migration.c:1866 tmigr_setup_groups() error: we previously assumed 'start' could be null (see line 1764)

Yes, the code is prone to that problem, but the two callers do the right
thing. Though this can be simplified.

Thanks

        tglx
---
 kernel/time/timer_migration.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/kernel/time/timer_migration.c
+++ b/kernel/time/timer_migration.c
@@ -1750,12 +1750,12 @@ static void tmigr_connect_child_parent(s
 	trace_tmigr_connect_child_parent(child);
 }
 
-static int tmigr_setup_groups(unsigned int cpu, unsigned int node,
-			      struct tmigr_group *start, bool activate)
+static int tmigr_setup_groups(unsigned int cpu, unsigned int node, struct tmigr_group *start)
 {
 	struct tmigr_group *group, *child, **stack;
 	int i, top = 0, err = 0, start_lvl = 0;
 	bool root_mismatch = false;
+	bool activate = false;
 
 	stack = kcalloc(tmigr_hierarchy_levels, sizeof(*stack), GFP_KERNEL);
 	if (!stack)
@@ -1764,6 +1764,7 @@ static int tmigr_setup_groups(unsigned i
 	if (start) {
 		stack[start->level] = start;
 		start_lvl = start->level + 1;
+		activate = true;
 	}
 
 	if (tmigr_root)
@@ -1893,7 +1894,7 @@ static int tmigr_add_cpu(unsigned int cp
 
 	guard(mutex)(&tmigr_mutex);
 
-	ret = tmigr_setup_groups(cpu, node, NULL, false);
+	ret = tmigr_setup_groups(cpu, node, NULL);
 
 	/* Root has changed? Connect the old one to the new */
 	if (ret >= 0 && old_root && old_root != tmigr_root) {
@@ -1910,7 +1911,7 @@ static int tmigr_add_cpu(unsigned int cp
 		 * otherwise the old root may not be active as expected.
 		 */
 		WARN_ON_ONCE(!per_cpu_ptr(&tmigr_cpu, raw_smp_processor_id())->available);
-		ret = tmigr_setup_groups(-1, old_root->numa_node, old_root, true);
+		ret = tmigr_setup_groups(-1, old_root->numa_node, old_root);
 	}
 
 	return ret;