Re: [tip: x86/mm] x86/mm/pat: Take cpa_lock around large-page collapse

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jul 16, 2026 at 08:01:07AM -0000, tip-bot2 for Denis V. Lunev wrote:
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index e9b4083..b1e780a 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -417,6 +417,8 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
>  	int collapsed = 0;
>  	int i;
>  
> +	spin_lock(&cpa_lock);
> +
>  	if (cpa->flags & (CPA_PAGES_ARRAY | CPA_ARRAY)) {
>  		for (i = 0; i < cpa->numpages; i++)
>  			collapsed += collapse_large_pages(__cpa_addr(cpa, i),
> @@ -430,8 +432,10 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
>  			collapsed += collapse_large_pages(addr, &pgtables);
>  	}
>  
> -	if (!collapsed)
> +	if (!collapsed) {
> +		spin_unlock(&cpa_lock);
>  		return;
> +	}
>  
>  	flush_tlb_all();
>  
> @@ -439,6 +443,8 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
>  		list_del(&ptdesc->pt_list);
>  		pagetable_free(ptdesc);
>  	}
> +
> +	spin_unlock(&cpa_lock);
>  }
>  
>  static void cpa_flush(struct cpa_data *cpa, int cache)

*groan*

Can we pretty please write it like so?


diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 1f2a2ba9ce57..f90f90bd879f 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -417,7 +417,7 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
 	int collapsed = 0;
 	int i;
 
-	spin_lock(&cpa_lock);
+	guard(spinlock)(&cpa_lock);
 
 	if (cpa->flags & (CPA_PAGES_ARRAY | CPA_ARRAY)) {
 		for (i = 0; i < cpa->numpages; i++)
@@ -432,10 +432,8 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
 			collapsed += collapse_large_pages(addr, &pgtables);
 	}
 
-	if (!collapsed) {
-		spin_unlock(&cpa_lock);
+	if (!collapsed)
 		return;
-	}
 
 	flush_tlb_all();
 
@@ -443,8 +441,6 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa)
 		list_del(&ptdesc->pt_list);
 		pagetable_free(ptdesc);
 	}
-
-	spin_unlock(&cpa_lock);
 }
 
 static void cpa_flush(struct cpa_data *cpa, int cache)