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Subject: Re: Can kfree() sleep at runtime?
Date:   Thu, 31 May 2018 18:34:45 -0700
In-Reply-To: <066df211-4d1e-787b-b89d-31b8827ea7a5@gmail.com>
Cc:     Christopher Lameter <cl@linux.com>,
        Matthew Wilcox <willy@infradead.org>, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To:     Jia-Ju Bai <baijiaju1990@gmail.com>
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Jia-Ju Bai <baijiaju1990@gmail.com> wrote:

>=20
>=20
> On 2018/5/31 22:30, Christopher Lameter wrote:
>> On Thu, 31 May 2018, Matthew Wilcox wrote:
>>=20
>>>> 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.
>>=20
>> Ok that is a very contorted situation but how would a static checker =
deal
>> with that?
>=20
> 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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