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    Subject[032/105] nilfs2: fix data loss in mmap page write for hole blocks
    2.6.38-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

    commit 34094537943113467faee98fe67c8a3d3f9a0a8b upstream.

    >From the result of a function test of mmap, mmap write to shared pages
    turned out to be broken for hole blocks. It doesn't write out filled
    blocks and the data will be lost after umount. This is due to a bug
    that the target file is not queued for log writer when filling hole
    blocks.

    Also, nilfs_page_mkwrite function exits normal code path even after
    successfully filled hole blocks due to a change of block_page_mkwrite
    function; just after nilfs was merged into the mainline,
    block_page_mkwrite() started to return VM_FAULT_LOCKED instead of zero
    by the patch "mm: close page_mkwrite races" (commit:
    b827e496c893de0c). The current nilfs_page_mkwrite() is not handling
    this value properly.

    This corrects nilfs_page_mkwrite() and will resolve the data loss
    problem in mmap write.

    [This should be applied to every kernel since 2.6.30 but a fix is
    needed for 2.6.37 and prior kernels]

    Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Tested-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    fs/nilfs2/file.c | 11 +++++------
    1 file changed, 5 insertions(+), 6 deletions(-)

    --- a/fs/nilfs2/file.c
    +++ b/fs/nilfs2/file.c
    @@ -72,10 +72,9 @@ static int nilfs_page_mkwrite(struct vm_
    /*
    * check to see if the page is mapped already (no holes)
    */
    - if (PageMappedToDisk(page)) {
    - unlock_page(page);
    + if (PageMappedToDisk(page))
    goto mapped;
    - }
    +
    if (page_has_buffers(page)) {
    struct buffer_head *bh, *head;
    int fully_mapped = 1;
    @@ -90,7 +89,6 @@ static int nilfs_page_mkwrite(struct vm_

    if (fully_mapped) {
    SetPageMappedToDisk(page);
    - unlock_page(page);
    goto mapped;
    }
    }
    @@ -105,16 +103,17 @@ static int nilfs_page_mkwrite(struct vm_
    return VM_FAULT_SIGBUS;

    ret = block_page_mkwrite(vma, vmf, nilfs_get_block);
    - if (unlikely(ret)) {
    + if (ret != VM_FAULT_LOCKED) {
    nilfs_transaction_abort(inode->i_sb);
    return ret;
    }
    + nilfs_set_file_dirty(inode, 1 << (PAGE_SHIFT - inode->i_blkbits));
    nilfs_transaction_commit(inode->i_sb);

    mapped:
    SetPageChecked(page);
    wait_on_page_writeback(page);
    - return 0;
    + return VM_FAULT_LOCKED;
    }

    static const struct vm_operations_struct nilfs_file_vm_ops = {



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