On Mon, Apr 23, 2007 at 10:39:56PM +0400, Oleg Nesterov wrote: > On 04/23, Gautham R Shenoy wrote: > > > > On Sat, Apr 21, 2007 at 01:12:09AM +0400, Oleg Nesterov wrote: > > > On 04/19, Gautham R Shenoy wrote: > > > > > > > > @@ -63,12 +74,16 @@ void refrigerator(void) > > > > recalc_sigpending(); /* We sent fake signal, clean it up */ > > > > spin_unlock_irq(¤t->sighand->siglock); > > > > > > > > + task_lock(current); > > > > for (;;) { > > > > set_current_state(TASK_UNINTERRUPTIBLE); > > > > if (!frozen(current)) > > > > break; > > > > + task_unlock(current); > > > > schedule(); > > > > + task_lock(current); > > > > } > > > > + task_unlock(current); > > > > pr_debug("%s left refrigerator\n", current->comm); > > > > current->state = save; > > > > > > Just curious, why this change? > > > > This can race with hold_freezer_for_task() calling thaw_process. Earlier > > thaw_process(p) was called only after the process 'p' was frozen. > > Now with hold_freezer_for_task(), we can as well call thaw_process(p) > > when 'p' is in the freezing stage. Hence the task_lock. > > hold_freezer_for_task()->thaw_process(p) will wake up the task. Or the > caller of refrigerator will notice "!frozen()". Note that refrigerator() > sets PF_FROZEN under task_lock(). > > In fact we have the same issue when thaw_tasks()->thaw_process(p) happens > when the freezing fails. In that case 'p' may be not frozen.
Yes. I guess I was being too cautious :) > > > > Also, you are planning to add different freezing states (FE_HOTPLUG_CPU, > > > FE_SUSPEND, etc). In that case each of them needs a separate .count, > > > because > > > it should be negative when try_to_freeze_tasks() returns. Now consider > > > the case when we are doing freeze_processes(FE_A | FE_B) ... > > > > So can't we in that case find out the weight of the freeze_event variable > > and > > subtract that weight from the count (if the count is <=0 ) ? > > Probably yes... but if we are speaking about kthrad_stop() only, this could > be afaics solved in more simple way, as Rafael suggests. I agree on this one. kthread_stop appears to be the only valid place where such a correction is required. So Rafael's approach makes sense here. > > Oleg. > Thanks and Regards gautham. -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!" - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/