linux-kernel - Re: Can kfree() sleep at runtime?

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Message-Id: <0875D539-4B35-402D-9CCA-09BBA8DDB46E@gmail.com>
Date:   Thu, 31 May 2018 18:34:45 -0700
From:   Nadav Amit <nadav.amit@...il.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     Christopher Lameter <cl@...ux.com>,
        Matthew Wilcox <willy@...radead.org>, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Can kfree() sleep at runtime?

Jia-Ju Bai <baijiaju1990@...il.com> wrote:

> 
> 
> On 2018/5/31 22:30, Christopher Lameter wrote:
>> On Thu, 31 May 2018, Matthew Wilcox wrote:
>> 
>>>> Freeing a page in the page allocator also was traditionally not sleeping.
>>>> That has changed?
>>> No.  "Your bug" being "The bug in your static analysis tool".  It probably
>>> isn't following the data flow correctly (or deeply enough).
>> Well ok this is not going to trigger for kfree(), this is x86 specific and
>> requires CONFIG_DEBUG_PAGEALLOC and a free of a page in a huge page.
>> 
>> Ok that is a very contorted situation but how would a static checker deal
>> with that?
> 
> I admit that my tool does not follow the data flow well, and I need to improve it.
> In this case of kfree(), I want know how the data flow leads to my mistake.

Note that is only enabled in debug mode:

static inline void
kernel_map_pages(struct page *page, int numpages, int enable)
{
        if (!debug_pagealloc_enabled())
                return;

        __kernel_map_pages(page, numpages, enable);
}

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