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    Subject[PATCH 5.15 881/917] mm, thp: fix incorrect unmap behavior for private pages
    Date
    From: Rongwei Wang <rongwei.wang@linux.alibaba.com>

    commit 8468e937df1f31411d1e127fa38db064af051fe5 upstream.

    When truncating pagecache on file THP, the private pages of a process
    should not be unmapped mapping. This incorrect behavior on a dynamic
    shared libraries which will cause related processes to happen core dump.

    A simple test for a DSO (Prerequisite is the DSO mapped in file THP):

    int main(int argc, char *argv[])
    {
    int fd;

    fd = open(argv[1], O_WRONLY);
    if (fd < 0) {
    perror("open");
    }

    close(fd);
    return 0;
    }

    The test only to open a target DSO, and do nothing. But this operation
    will lead one or more process to happen core dump. This patch mainly to
    fix this bug.

    Link: https://lkml.kernel.org/r/20211025092134.18562-3-rongwei.wang@linux.alibaba.com
    Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs")
    Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
    Tested-by: Xu Yu <xuyu@linux.alibaba.com>
    Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
    Cc: Song Liu <song@kernel.org>
    Cc: William Kucharski <william.kucharski@oracle.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Yang Shi <shy828301@gmail.com>
    Cc: Mike Kravetz <mike.kravetz@oracle.com>
    Cc: Collin Fijalkovich <cfijalkovich@google.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>
    ---
    fs/open.c | 11 ++++++++++-
    1 file changed, 10 insertions(+), 1 deletion(-)

    --- a/fs/open.c
    +++ b/fs/open.c
    @@ -857,8 +857,17 @@ static int do_dentry_open(struct file *f
    */
    smp_mb();
    if (filemap_nr_thps(inode->i_mapping)) {
    + struct address_space *mapping = inode->i_mapping;
    +
    filemap_invalidate_lock(inode->i_mapping);
    - truncate_pagecache(inode, 0);
    + /*
    + * unmap_mapping_range just need to be called once
    + * here, because the private pages is not need to be
    + * unmapped mapping (e.g. data segment of dynamic
    + * shared libraries here).
    + */
    + unmap_mapping_range(mapping, 0, 0, 0);
    + truncate_inode_pages(mapping, 0);
    filemap_invalidate_unlock(inode->i_mapping);
    }
    }

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