linux-kernel - Re: [PATCH 4/8] mm/vmalloc: Remove cond_resched() in vm_area_alloc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aJSMfJhBOltRiSUh@tiehlicka>
Date: Thu, 7 Aug 2025 13:22:36 +0200
From: Michal Hocko <mhocko@...e.com>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, Baoquan He <bhe@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/8] mm/vmalloc: Remove cond_resched() in
 vm_area_alloc_pages()

On Thu 07-08-25 09:58:06, Uladzislau Rezki wrote:
> The vm_area_alloc_pages() function uses cond_resched() to yield the
> CPU during potentially long-running loops. However, these loops are
> not considered long-running under normal conditions.

To be more precise they can take long if they dive into the page
allocator but that already involves cond_rescheds where appropriate so
these are not needed in fact.

> In non-blocking
> contexts, calling cond_resched() is inappropriate also.
> 
> Remove these calls to ensure correctness for blocking/non-blocking
> contexts. This also simplifies the code path. In fact, a slow path
> of page allocator already includes reschedule points to mitigate
> latency.
> 
> This patch was tested for !CONFIG_PREEMPT kernel and with large
> allocation chunks(~1GB), without triggering any "BUG: soft lockup"
> warnings.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!
> ---
>  mm/vmalloc.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 81b6d3bde719..b0255e0c74b3 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3633,7 +3633,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  							pages + nr_allocated);
>  
>  			nr_allocated += nr;
> -			cond_resched();
>  
>  			/*
>  			 * If zero or pages were obtained partly,
> @@ -3675,7 +3674,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  		for (i = 0; i < (1U << order); i++)
>  			pages[nr_allocated + i] = page + i;
>  
> -		cond_resched();
>  		nr_allocated += 1U << order;
>  	}
>  
> -- 
> 2.39.5
> 

-- 
Michal Hocko
SUSE Labs