Messages in this thread Patch in this message | | | Date | Wed, 1 Feb 2017 18:19:11 +0100 | From | Oleg Nesterov <> | Subject | Re: Question about replacing while_each_thread(). |
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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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