(Resending with 80 column restriction) > -----Original Message----- > From: Pavel Machek [mailto:pavel@xxxxxx] > Sent: Sunday, November 08, 2009 1:57 PM > To: Dasgupta, Romit > Cc: Rafael J. Wysocki; linux-omap@xxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx; linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > Subject: Re: [PATCH 1/1] PM: Thaws refrigerated and to be > exited kernel threads > > On Sun 2009-11-08 09:52:52, Dasgupta, Romit wrote: > > > Subject: Re: [PATCH 1/1] PM: Thaws refrigerated and to be > exited kernel > > > threads > > > > > > Hi! > > > > > > > Kicks out a frozen thread from the refrigerator when an > active thread has > > > > invoked kthread_stop on the frozen thread. > ... > > > > @@ -49,7 +50,7 @@ void refrigerator(void) > > > > > > > > for (;;) { > > > > set_current_state(TASK_UNINTERRUPTIBLE); > > > > - if (!frozen(current)) > > > > + if (!frozen(current) || (!current->mm > && kthread_should_stop())) > > > > break; > > > > schedule(); > > > > > > Well, what if the thread does some processing before > stopping? That > > > would break refrigerator assumptions... > > > > The suspend thread will block until the 'to be stopped' > thread clears up. That is what any call to kthread_stop would > boil down to. The target thread would anyway be out of the > refrigerator so I am not sure what assumption you mean here. > Eventually, the target thread would clear up and wake up the > suspend thread and then things would go on as usual. > > (Please format to 80 columns). > > No, I do not get it. > > Lets say we have > > evil_data_writer thread that needs to be stopped becuase it writes to > filesystem > > nofreeze random_stopper thread > > now we create the suspend image, and start writing it out. But that's > okay, evil_data_writer is stopped so it can't do no harm. But now > random_stopper decides to thread_stop() the evil_data_writer, and this > new code allows it to exit the refrigerator, *do some writing*, and > then stop. > > That's bad, right? evil_data_writer will enter refrigerator after invoking 'try_to_freeze'. This should be followed by a call to kthread_should_stop. There it decides if it needs to exit the thread (after cleanups if necessary) or not. I have seen that the bdi_writeback_task function is like that. It does not care if there is pending data to be written if it detects that someone have invoked a 'kthread_stop' on it. It simply exits. I have seen some other kernel threads that do not follow this and I think that probably is not right. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
