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Date:   Tue, 12 Jan 2021 14:27:11 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Rokudo Yan <wu-yan@....com>
Cc:     <mgorman@...hsingularity.net>, <aarcange@...hat.com>,
        <haiwang.fu@....com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <rientjes@...gle.com>, <tang.ding@....com>,
        <vbabka@...e.cz>, <xiushui.ye@....com>
Subject: Re: [PATCH] mm, compaction: move high_pfn to the for loop scope.

On Tue, 12 Jan 2021 17:47:20 +0800 Rokudo Yan <wu-yan@....com> wrote:

> In fast_isolate_freepages, high_pfn will be used if a prefered one(PFN >= low_fn) not found. But the high_pfn
> is not reset before searching an free area, so when it was used as freepage, it may from another free area searched before.
> And move_freelist_head(freelist, freepage) will have unexpected behavior(eg. corrupt the MOVABLE freelist)
> 
> Unable to handle kernel paging request at virtual address dead000000000200
> Mem abort info:
>   ESR = 0x96000044
>   Exception class = DABT (current EL), IL = 32 bits
>   SET = 0, FnV = 0
>   EA = 0, S1PTW = 0
> Data abort info:
>   ISV = 0, ISS = 0x00000044
>   CM = 0, WnR = 1
> [dead000000000200] address between user and kernel address ranges
> 
> -000|list_cut_before(inline)
> -000|move_freelist_head(inline)
> -000|fast_isolate_freepages(inline)
> -000|isolate_freepages(inline)
> -000|compaction_alloc(?, ?)
> -001|unmap_and_move(inline)
> -001|migrate_pages([NSD:0xFFFFFF80088CBBD0] from = 0xFFFFFF80088CBD88, [NSD:0xFFFFFF80088CBBC8] get_new_p
> -002|__read_once_size(inline)
> -002|static_key_count(inline)
> -002|static_key_false(inline)
> -002|trace_mm_compaction_migratepages(inline)
> -002|compact_zone(?, [NSD:0xFFFFFF80088CBCB0] capc = 0x0)
> -003|kcompactd_do_work(inline)
> -003|kcompactd([X19] p = 0xFFFFFF93227FBC40)
> -004|kthread([X20] _create = 0xFFFFFFE1AFB26380)
> -005|ret_from_fork(asm)
> ---|end of frame
> 
> The issue was reported on an smart phone product with 6GB ram and 3GB zram as swap device.
> 
> This patch fixes the issue by reset high_pfn before searching each free area, which ensure
> freepage and freelist match when call move_freelist_head in fast_isolate_freepages().
> 
> Link: http://lkml.kernel.org/r/20190118175136.31341-12-mgorman@techsingularity.net
> Fixes: 5a811889de10f1eb ("mm, compaction: use free lists to quickly locate a migration target")

Could you please send a Signed-off-by: for this patch, as per
Documentation/process/submitting-patches.rst?

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