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    SubjectRe: [PATCH 4/4] files: doc update

    Update files documentation to mention the need for reloading
    fdtable pointer if ->file_lock is dropped.

    Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
    ---


    Documentation/filesystems/files.txt | 20 ++++++++++++++++++++
    1 files changed, 20 insertions(+)

    diff -puN Documentation/filesystems/files.txt~files-doc-update Documentation/filesystems/files.txt
    --- linux-2.6.12-mm1-fix/Documentation/filesystems/files.txt~files-doc-update 2005-06-26 06:01:40.000000000 +0530
    +++ linux-2.6.12-mm1-fix-dipankar/Documentation/filesystems/files.txt 2005-06-26 06:13:09.000000000 +0530
    @@ -101,3 +101,23 @@ the fdtable structure -
    API. If they are looked up lock-free, rcu_dereference()
    must be used. However it is advisable to use files_fdtable()
    and fcheck()/fcheck_files() which take care of these issues.
    +
    +7. While updating, the fdtable pointer must be looked up while
    + holding files->file_lock. If ->file_lock is dropped, then
    + another thread expand the files thereby creating a new
    + fdtable and making the earlier fdtable pointer stale.
    + For example :
    +
    + spin_lock(&files->file_lock);
    + fd = locate_fd(files, file, start);
    + if (fd >= 0) {
    + /* locate_fd() may have expanded fdtable, load the ptr */
    + fdt = files_fdtable(files);
    + FD_SET(fd, fdt->open_fds);
    + FD_CLR(fd, fdt->close_on_exec);
    + spin_unlock(&files->file_lock);
    + .....
    +
    + Since locate_fd() can drop ->file_lock (and reacquire ->file_lock),
    + the fdtable pointer (fdt) must be loaded after locate_fd().
    +
    _
    -
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