linux-kernel - Re: [PATCH] mm: remove duplicated vma->vm

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Date:   Mon, 11 Sep 2023 10:04:43 +0800
From:   Xiu Jianfeng <xiujianfeng@...weicloud.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Xiu Jianfeng <xiujianfeng@...weicloud.com>
Cc:     Liam.Howlett@...cle.com, willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: remove duplicated vma->vm_flags check when expanding
 stack

Hi,

On 2023/9/11 5:26, Andrew Morton wrote:
> On Wed,  6 Sep 2023 10:33:12 +0000 Xiu Jianfeng <xiujianfeng@...weicloud.com> wrote:
> 
>> expand_upwards() and expand_downwards() will return -EFAULT if VM_GROWSUP
>> or VM_GROWSDOWN is not correctly set in vma->vm_flags, however in
>> !CONFIG_STACK_GROWSUP case, expand_stack_locked() returns -EINVAL first
>> if !(vma->vm_flags & VM_GROWSDOWN) before calling expand_downwards(), to
>> keep the consistency with CONFIG_STACK_GROWSUP case, remove this check.
> 
> What are the user-visible effects of this change?
> 
> Do you believe this fix should be backported into earlier kernel versions?

The usages of this function are as bellow:

A:fs/exec.c
ret = expand_stack_locked(vma, stack_base);
if (ret)
	ret = -EFAULT;

or

B:mm/memory.c mm/mmap.c
if (expand_stack_locked(vma, addr))
	return NULL;

which means the return value will not propagate to other places, so I
believe there is no user-visible effects of this change, and it's
unnecessary to backport to earlier versions.