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    Subject[PATCH] proc-remove-races-from-proc_id_readdir-factor-out-tgid-increment
    On 11/19, Eric W. Biederman wrote:
    >
    > So to fix the problem this patch modifies next_tgid() to return
    > both a tgid and the task struct in question.
    >
    > A structure is introduced to return these values because it is
    > slightly cleaner and easier to optimize, and the resulting code
    > is a little shorter.

    Nice. Perhaps we can also factor out the incrementing of iter.tgid? Lessens
    the generated code, and (imho) cleanups the source a little bit.

    (untested, 2.6.24-rc2-mm1 doesn't boot on my machine)

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

    --- PT/fs/proc/base.c~ 2007-11-20 19:00:05.000000000 +0300
    +++ PT/fs/proc/base.c 2007-11-20 19:06:28.000000000 +0300
    @@ -2378,6 +2378,7 @@ static struct tgid_iter next_tgid(struct
    rcu_read_lock();
    retry:
    iter.task = NULL;
    + iter.tgid++;
    pid = find_ge_pid(iter.tgid, ns);
    if (pid) {
    iter.tgid = pid_nr_ns(pid, ns);
    @@ -2394,10 +2395,8 @@ retry:
    * found doesn't happen to be a thread group leader.
    * As we don't care in the case of readdir.
    */
    - if (!iter.task || !has_group_leader_pid(iter.task)) {
    - iter.tgid += 1;
    + if (!iter.task || !has_group_leader_pid(iter.task))
    goto retry;
    - }
    get_task_struct(iter.task);
    }
    rcu_read_unlock();
    @@ -2434,10 +2433,8 @@ int proc_pid_readdir(struct file * filp,

    ns = filp->f_dentry->d_sb->s_fs_info;
    iter.task = NULL;
    - iter.tgid = filp->f_pos - TGID_OFFSET;
    - for (iter = next_tgid(ns, iter);
    - iter.task;
    - iter.tgid += 1, iter = next_tgid(ns, iter)) {
    + iter.tgid = filp->f_pos - TGID_OFFSET - 1;
    + while ((iter = next_tgid(ns, iter)).task) {
    filp->f_pos = iter.tgid + TGID_OFFSET;
    if (proc_pid_fill_cache(filp, dirent, filldir, iter) < 0) {
    put_task_struct(iter.task);
    -
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