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    Subject[PATCH 5.10 102/120] mm, compaction: move high_pfn to the for loop scope
    Date
    From: Rokudo Yan <wu-yan@tcl.com>

    commit 74e21484e40bb8ce0f9828bbfe1c9fc9b04249c6 upstream.

    In fast_isolate_freepages, high_pfn will be used if a prefered one (ie
    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. As
    a result 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)

    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
    Link: https://lkml.kernel.org/r/20210112094720.1238444-1-wu-yan@tcl.com
    Fixes: 5a811889de10f1eb ("mm, compaction: use free lists to quickly locate a migration target")
    Signed-off-by: Rokudo Yan <wu-yan@tcl.com>
    Acked-by: Mel Gorman <mgorman@techsingularity.net>
    Acked-by: Vlastimil Babka <vbabka@suse.cz>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/compaction.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/mm/compaction.c
    +++ b/mm/compaction.c
    @@ -1302,7 +1302,7 @@ fast_isolate_freepages(struct compact_co
    {
    unsigned int limit = min(1U, freelist_scan_limit(cc) >> 1);
    unsigned int nr_scanned = 0;
    - unsigned long low_pfn, min_pfn, high_pfn = 0, highest = 0;
    + unsigned long low_pfn, min_pfn, highest = 0;
    unsigned long nr_isolated = 0;
    unsigned long distance;
    struct page *page = NULL;
    @@ -1347,6 +1347,7 @@ fast_isolate_freepages(struct compact_co
    struct page *freepage;
    unsigned long flags;
    unsigned int order_scanned = 0;
    + unsigned long high_pfn = 0;

    if (!area->nr_free)
    continue;

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