linux-kernel - Re: [PATCH v2 2/3] mm: vmalloc: Switch to find_unlink_vmap_area() in vm_unmap

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: <Y6QaTqq8KXv3Dg7p@infradead.org>
Date:   Thu, 22 Dec 2022 00:50:22 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>, Baoquan He <bhe@...hat.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH v2 2/3] mm: vmalloc: Switch to find_unlink_vmap_area() in
 vm_unmap_ram()

Looks good:

Reviewed-by: Christoph Hellwig <hch@....de>

On Wed, Dec 21, 2022 at 06:44:53PM +0100, Uladzislau Rezki (Sony) wrote:
> Switch from find_vmap_area() to find_unlink_vmap_area() to prevent
> a double access to the vmap_area_lock: one for finding area, second
> time is for unlinking from a tree.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> ---
>  mm/vmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 28030d2441f1..17e688cc7357 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2251,7 +2251,7 @@ void vm_unmap_ram(const void *mem, unsigned int count)
>  		return;
>  	}
>  
> -	va = find_vmap_area(addr);
> +	va = find_unlink_vmap_area(addr);

I can't find find_unlink_vmap_area in current -next, but shouldn't
this also switch from free_vmap_area_noflush to something that
doesn't unlink from the list and avoid the lock?

In general the code could probably use a bit of refactoring to
split unmapping from freeing.