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

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Date:   Fri, 1 Jun 2018 09:18:45 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Christopher Lameter <cl@...ux.com>
Cc:     Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        Mel Gorman <mgorman@...hsingularity.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Can kfree() sleep at runtime?



On 2018/5/31 22:09, Christopher Lameter wrote:
> On Thu, 31 May 2018, Jia-Ju Bai wrote:
>
>> I write a static analysis tool (DSAC), and it finds that kfree() can sleep.
> That should not happen.
>
>> Here is the call path for kfree().
>> Please look at it *from the bottom up*.
>>
>> [FUNC] alloc_pages(GFP_KERNEL)
>> arch/x86/mm/pageattr.c, 756: alloc_pages in split_large_page
>> arch/x86/mm/pageattr.c, 1283: split_large_page in __change_page_attr
>> arch/x86/mm/pageattr.c, 1391: __change_page_attr in __change_page_attr_set_clr
>> arch/x86/mm/pageattr.c, 2014: __change_page_attr_set_clr in __set_pages_np
>> arch/x86/mm/pageattr.c, 2034: __set_pages_np in __kernel_map_pages
>> ./include/linux/mm.h, 2488: __kernel_map_pages in kernel_map_pages
>> mm/page_alloc.c, 1074: kernel_map_pages in free_pages_prepare
> mapping pages in the page allocator can cause allocations?? How did that
> get in there?

Thanks for reply :)
I am also confused about it.

I get in here according to the definition of free_pages_prepare():
1022. static bool free_pages_prepare(...) {
              ...
1072.    arch_free_page(page, order);
1073.    kernel_poison_pages(page, 1 << order, 0);
1074.    kernel_map_pages(page, 1 << order, 0); // *Here*
1075.    kasan_free_pages(page, order);
1076.
1077.    return true;
1078. }


Best wishes,
Jia-Ju Bai