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SubjectRe: Question about replacing while_each_thread().
Hi Tetsuo,

On 02/01, Tetsuo Handa wrote:
>
> Is rcu_read_lock() sufficient (i.e.
>
> rcu_read_lock();
> for_each_process_thread(g, p) {
> (...snipped...)
> }
> rcu_read_unlock();
>
> is OK) for "can't go away" ?

Yes, this should work just fine,

> Likewise, IOPRIO_WHO_PGRP case are using
>
> rcu_read_lock();
> do {
> if ((pgrp) != NULL)
> hlist_for_each_entry_rcu((p), &(pgrp)->tasks[PIDTYPE_PGID], pids[PIDTYPE_PGID].node) {
> {
> struct task_struct *tg___ = p;
> do {
> (...snipped...)
> } while_each_thread(tg___, p);
> p = tg___;
> }
> if (PIDTYPE_PGID == PIDTYPE_PID)
> break;
> }
> } while (0);
> rcu_read_unlock();
>
> sequence which I guess it is unsafe as well.

Hmm, indeed, I forgot there is another while_each_thread() hidden in
do_each_pid_thread()

> In this case updating do_each_pid_thread() to use for_each_thread() and
> updating while_each_pid_thread() not to use while_each_thread() is
> the correct fix?

Yes, I think so, just

--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -191,10 +191,10 @@ pid_t pid_vnr(struct pid *pid);
#define do_each_pid_thread(pid, type, task) \
do_each_pid_task(pid, type, task) { \
struct task_struct *tg___ = task; \
- do {
+ for_each_thread(tg__, task) {

#define while_each_pid_thread(pid, type, task) \
- } while_each_thread(tg___, task); \
+ } \
task = tg___; \
} while_each_pid_task(pid, type, task)
#endif /* _LINUX_PID_H */


but perhaps we can also cleanup it... the usage of 'tg___' doesn't look nice
either way, so perhaps

#define do_each_pid_thread(pid, type, task) do { \
struct task_struct *tg___; \
do_each_pid_task(pid, type, tg___) { \
for_each_thread(tg__, task) {

#define while_each_pid_thread(pid, type, task) \
} \
} while_each_pid_task(pid, type, task); \
} while (0)

will look a bit better? up to you.

Oleg.

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