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    Subject[PATCH 5.14 035/125] mm, thp: bail out early in collapse_file for writeback page
    Date
    From: Rongwei Wang <rongwei.wang@linux.alibaba.com>

    commit 74c42e1baacf206338b1dd6b6199ac964512b5bb upstream.

    Currently collapse_file does not explicitly check PG_writeback, instead,
    page_has_private and try_to_release_page are used to filter writeback
    pages. This does not work for xfs with blocksize equal to or larger
    than pagesize, because in such case xfs has no page->private.

    This makes collapse_file bail out early for writeback page. Otherwise,
    xfs end_page_writeback will panic as follows.

    page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32
    aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so"
    flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback)
    raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8
    raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000
    page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u))
    page->mem_cgroup:ffff0000c3e9a000
    ------------[ cut here ]------------
    kernel BUG at include/linux/mm.h:1212!
    Internal error: Oops - BUG: 0 [#1] SMP
    Modules linked in:
    BUG: Bad page state in process khugepaged pfn:84ef32
    xfs(E)
    page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32
    libcrc32c(E) rfkill(E) aes_ce_blk(E) crypto_simd(E) ...
    CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: ...
    pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--)
    Call trace:
    end_page_writeback+0x1c0/0x214
    iomap_finish_page_writeback+0x13c/0x204
    iomap_finish_ioend+0xe8/0x19c
    iomap_writepage_end_bio+0x38/0x50
    bio_endio+0x168/0x1ec
    blk_update_request+0x278/0x3f0
    blk_mq_end_request+0x34/0x15c
    virtblk_request_done+0x38/0x74 [virtio_blk]
    blk_done_softirq+0xc4/0x110
    __do_softirq+0x128/0x38c
    __irq_exit_rcu+0x118/0x150
    irq_exit+0x1c/0x30
    __handle_domain_irq+0x8c/0xf0
    gic_handle_irq+0x84/0x108
    el1_irq+0xcc/0x180
    arch_cpu_idle+0x18/0x40
    default_idle_call+0x4c/0x1a0
    cpuidle_idle_call+0x168/0x1e0
    do_idle+0xb4/0x104
    cpu_startup_entry+0x30/0x9c
    secondary_start_kernel+0x104/0x180
    Code: d4210000 b0006161 910c8021 94013f4d (d4210000)
    ---[ end trace 4a88c6a074082f8c ]---
    Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt

    Link: https://lkml.kernel.org/r/20211022023052.33114-1-rongwei.wang@linux.alibaba.com
    Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
    Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
    Signed-off-by: Xu Yu <xuyu@linux.alibaba.com>
    Suggested-by: Yang Shi <shy828301@gmail.com>
    Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Reviewed-by: Yang Shi <shy828301@gmail.com>
    Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Song Liu <song@kernel.org>
    Cc: William Kucharski <william.kucharski@oracle.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    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/khugepaged.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    --- a/mm/khugepaged.c
    +++ b/mm/khugepaged.c
    @@ -1763,6 +1763,10 @@ static void collapse_file(struct mm_stru
    filemap_flush(mapping);
    result = SCAN_FAIL;
    goto xa_unlocked;
    + } else if (PageWriteback(page)) {
    + xas_unlock_irq(&xas);
    + result = SCAN_FAIL;
    + goto xa_unlocked;
    } else if (trylock_page(page)) {
    get_page(page);
    xas_unlock_irq(&xas);
    @@ -1798,7 +1802,8 @@ static void collapse_file(struct mm_stru
    goto out_unlock;
    }

    - if (!is_shmem && PageDirty(page)) {
    + if (!is_shmem && (PageDirty(page) ||
    + PageWriteback(page))) {
    /*
    * khugepaged only works on read-only fd, so this
    * page is dirty because it hasn't been flushed

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