On Monday, February 11, 2013 11:11:40 AM Miklos Szeredi wrote: > On Mon, Feb 11, 2013 at 12:31 AM, Rafael J. Wysocki <r...@sisk.pl> wrote: > > On Sunday, February 10, 2013 07:55:05 PM Pavel Machek wrote: > > >> Well, from freezer you need: > >> > >> 1) user process frozen. > >> > >> 2) essential locks _not_ held so that block devices are still functional. > >> > >> > > > mmap... what is problem with mmap? For suspend, memory is powered, so > >> > > > you can permit people changing it. > >> > > > >> > > Suppose mmap is used to make the registers of some device available to > >> > > user > >> > > space. Yes, that can happen. > >> > >> "Don't do it, then". Yes, can happen, but hopefully is not too common > >> these days. [And... freezer doing 1) but not 2) would be enough to > >> handle that. Freezer doing 1) but not 2) would also be simpler...] > > > > Again, I'm not sure what you mean. > > > > Are you trying to say that it would be OK to freeze user space tasks in > > the D state? > > I think that's what Pavel is saying. Processes in D state sleeping > on non-device mutexes _are_ actually OK to freeze. And that would > nicely solve the fuse freeze problem.
That's potentially deeadlock-prone, because a task waiting for mutex X may very well be holding mutex Y, so if there's another task waiting for mutex Y, it needs to be frozen at the same time. > The only little detail is how do we implement that... This means the only way I can see would be to hack the mutex code so that the try_to_freeze() was called for user space tasks after the sched_preempt_enable_no_resched() before schedule(). That shouldn't be a big deal performance-wise, because we are in the slow path anyway then. I'm not sure if Peter Z will like it, though. Moreover, a task waiting for a mutex may be holding a semaphore or be participating in some other mutual-exclusion mechanism, so we'd need to address them all. Plus, as noted by Pavel, freezing those things would make it difficult to save hibernation images to us. What about having a "freeze me after all of my children" flag that will be inherited from parents? Would that help the fuse case? Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/