On Wednesday, 31 January 2007 16:48, Alan Stern wrote: > On Wed, 31 Jan 2007, Rafael J. Wysocki wrote: > > > On Tuesday, 30 January 2007 23:32, Rafael J. Wysocki wrote: > > > [Added linux-pm to the Cc list, because I'm going to talk about things > > > that > > > I know only from reading the code.] > > > > > > On Tuesday, 30 January 2007 17:50, Oliver Neukum wrote: > > > > Am Dienstag, 30. Januar 2007 17:32 schrieb Rafael J. Wysocki: > > > > > However, you can always inspect the PF_FROZEN flag of the tasks in > > > > > question > > > > > if that's practicable. > > > > > > > > What would I do with that information? Ignore completion of IO? > > > > > > I probably should say "that depends", but that wouldn't be very helpful. > > > > > > Getting back to your initial question, which is if wake_up() may be called > > > from a driver's .resume() routine, I think the answer is no, it may not, > > > because in that case the "notified" tasks would be removed from the wait > > > queue, but the refrigerator() would (wrongly) restore their states as > > > TASK_UNINTERRUPTIBLE (or TASK_INTERRUPTIBLE for wake_up_interruptible()). > > Even though I'm late to this thread, here are some additional thoughts... > > Rafael is wrong; wake_up() doesn't remove a task from a wait queue. It > makes the task runnable, and then the task removes itself from the wait > queue after verifying that the necessary condition has been satisfied. > > Thus calling wake_up() on a task in the refrigerator will accomplish > nothing -- no good and no harm. The task will remain frozen, and when it > is unfrozen it will realize that the condition has been satisfied and will > remove itself from the wait queue.
That's the point I wasn't quite sure of. > > > Generally, you are safe if your driver only calls wake_up() from a process > > > context, but not from .resume() or .suspend() routines (or from an > > > unfreezeable kernel thread). > > > > Ah, sorry, I've just realized I was wrong. Processes in > > TASK_UNINTERRUPTIBLE > > cannot be frozen! So, the above only applies to wake_up_interruptible(). > > > > You don't need to call wake_up() from .resume(), because there are no tasks > > to be notified this way and you shouldn't call wake_up_interruptible() from > > there. > > While it's true that one doesn't need to call wake_up() from .resume(), > you are overlooking the point of Oliver's question. .resume() can start > up an I/O operation which can then complete before the tasks are > defrosted. The I/O's completion routine generally _will_ end up calling > wake_up() on some still-frozen task. That's just as bad as calling it > yourself from within the resume routine. Okay, but since the tasks remove themselves from wait queues, there's no problem here. :-) Greetings, Rafael -- If you don't have the time to read, you don't have the time or the tools to write. - Stephen King - 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/