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    SubjectRe: [RFC][PATCH v2] readahead: introduce O_RANDOM_READ for POSIX_FADV_RANDOM
    On Fri, Jan 08, 2010 at 09:08:28PM +0800, Christoph Hellwig wrote:
    > Just thinking about this again, why don't you put the flag into
    > file->f_mode and the FMODE_* namespace given that we don't want it to be
    > settable from open?

    Good idea. To do that without race I would like to add ->f_lock to
    f_mode modifications at non-open time, like this. What do you think?

    ---
    vfs: take f_lock on modifying f_mode after open time

    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    ---
    fs/file_table.c | 2 ++
    fs/nfsd/nfs4state.c | 2 ++
    2 files changed, 4 insertions(+)

    --- linux.orig/fs/file_table.c 2010-01-09 10:50:24.000000000 +0800
    +++ linux/fs/file_table.c 2010-01-09 10:51:06.000000000 +0800
    @@ -394,7 +394,9 @@ retry:
    continue;
    if (!(f->f_mode & FMODE_WRITE))
    continue;
    + spin_lock(&f->f_lock);
    f->f_mode &= ~FMODE_WRITE;
    + spin_unlock(&f->f_lock);
    if (file_check_writeable(f) != 0)
    continue;
    file_release_write(f);
    --- linux.orig/fs/nfsd/nfs4state.c 2010-01-09 10:52:54.000000000 +0800
    +++ linux/fs/nfsd/nfs4state.c 2010-01-09 10:52:56.000000000 +0800
    @@ -1998,7 +1998,9 @@ nfs4_file_downgrade(struct file *filp, u
    {
    if (share_access & NFS4_SHARE_ACCESS_WRITE) {
    drop_file_write_access(filp);
    + spin_lock(&filp->f_lock);
    filp->f_mode = (filp->f_mode | FMODE_READ) & ~FMODE_WRITE;
    + spin_unlock(&filp->f_lock);
    }
    }


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