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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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