From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id B37174C81
	for <linux-kernel@vger.kernel.org>; Thu, 16 Jan 2025 04:01:39 +0000 (UTC)
Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201
ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;
	t=1737000099; cv=none; b=bM+DhTKAoZS98eyQXMEppf2zE3nT4uWhRLv/5c1Ad9M//OKl3SzVAiOO0ShPgZDPpm/B7dua8kbsrckdXqoJ+cR6bEa295rMYgtOjofDhPoxKv5S0GXco9PvpqA0EH5+FBtc6LPam9ECO741hUWdjp2BImGddw17ZsNRIK/nnvI=
ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org;
	s=arc-20240116; t=1737000099; c=relaxed/simple;
	bh=/A3EHbhjm/JMu8+qy59CDtweJJn9hEoeX0pag1cKcpY=;
	h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References:
	 Mime-Version:Content-Type; b=W3MstH/wn+ILndAAyD3BeVPxKb2xsoM5Lqrsjhr5q8pxsff4xXzgmnOWIpN9nLdGTxpYyuRP1DUQG3wcLRBBlI19JGgE3Bi17amKiLDQAe8Oe1HrrwSC4qESpjGtHIg7yZgNcrUgX6SO7OyYmA6lbx3nLznk0puF5Q7G5WnLMZI=
ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=2L7Cip36; arc=none smtp.client-ip=10.30.226.201
Authentication-Results: smtp.subspace.kernel.org;
	dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="2L7Cip36"
Received: by smtp.kernel.org (Postfix) with ESMTPSA id F077DC4CED6;
	Thu, 16 Jan 2025 04:01:38 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org;
	s=korg; t=1737000099;
	bh=/A3EHbhjm/JMu8+qy59CDtweJJn9hEoeX0pag1cKcpY=;
	h=Date:From:To:Cc:Subject:In-Reply-To:References:From;
	b=2L7Cip36NIW/dcUhC5QVzFHb+UTkkkvY3aXesgJJ+9ks6EcuuRmneiLYWYY4P+oHN
	 JRsRuOs/8e/4NEX9kDHQ3e57BlkOQ9ArQ/AFZLbCwpic9OXK/2OCMt0KvtjmEk+OEp
	 FqRQwrARMdinpGoAMRlnYvgyVFk4b/yRZPmOpSG0=
Date: Wed, 15 Jan 2025 20:01:38 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Liu Ye <liuye@kylinos.cn>
Cc: Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, jannh@google.com,
 vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/vma: Add VM_WARN_ON for commit_merge
Message-Id: <20250115200138.708adc518dd4f92f4fe7fae5@linux-foundation.org>
In-Reply-To: <20250116025005.55846-1-liuye@kylinos.cn>
References: <20250116025005.55846-1-liuye@kylinos.cn>
X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu)
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

On Thu, 16 Jan 2025 10:50:05 +0800 Liu Ye <liuye@kylinos.cn> wrote:

>     Add VM_WARN_ON to prevent 'adjust' from accessing NULL pointers
>     when 'adjust' is NULL and 'expanded' is false or 'adj_start' is
>     not zero.
>
> ...
>
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -641,6 +641,7 @@ static int commit_merge(struct vma_merge_struct *vmg,
>  
>  	init_multi_vma_prep(&vp, vmg->vma, adjust, remove, remove2);
>  
> +	VM_WARN_ON(!adjust && (!expanded || adj_start));
>  	VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
>  		   vp.anon_vma != adjust->anon_vma);
>  

This won't prevent a null deref.  It will emit a warning which
duplicates all the information which we're about to emit from the oops
handler.

Are there any reports of an oops from a NULL deref of `adjust'?