[PATCH] x86/resctrl: Remove lockdep annotation that triggers false positive

[PATCH] x86/resctrl: Remove lockdep annotation that triggers false positive

[James Morse]

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

Re: [PATCH] x86/resctrl: Remove lockdep annotation that triggers false positive

[Reinette Chatre]

Hi James,

On 2/21/2024 4:23 AM, James Morse wrote:
> 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))

I agree with this change. Could you please base it on x86/cache
branch of tip? 

Thank you

Reinette

Re: [PATCH] x86/resctrl: Remove lockdep annotation that triggers false positive

[Borislav Petkov]

On Wed, Feb 21, 2024 at 08:48:24AM -0800, Reinette Chatre wrote:
> I agree with this change. Could you please base it on x86/cache
> branch of tip?

No need - whacked it into submission.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH] x86/resctrl: Remove lockdep annotation that triggers false positive

[Reinette Chatre]

On 2/22/2024 7:16 AM, Borislav Petkov wrote:
> On Wed, Feb 21, 2024 at 08:48:24AM -0800, Reinette Chatre wrote:
>> I agree with this change. Could you please base it on x86/cache
>> branch of tip?
> 
> No need - whacked it into submission.

Thank you very much Boris.

Reinette