On Wed, 29 Oct 2008, Alan Stern wrote: > On Wed, 29 Oct 2008, Miklos Szeredi wrote: > > I did a random sampling of ->suspend() callbacks, and they don't seem > > to be taking mutexes. Does that happen at all? > > It does, particularly among drivers that do runtime PM, which is > becoming more and more important. > > Besides, suspend has to synchronize with I/O somehow. Right now that > is handled by making suspend wait until no tasks are doing I/O (because > they are all frozen). What about async I/O? > If you allow tasks to be frozen at more or less > arbitrary times, while holding arbitrary locks, then you may end up > freezing a task that's in the middle of I/O. That should certainly > block the suspend (not to mention messing up the I/O operation). What is the middle of I/O? Depending the type of I/O it could be messed up regardless of whether tasks happen to be in userspace or not (e.g. printing). And some types of I/O are already mostly decoupled from userspace (file I/O, networking), so the userspace freezing shoudln't make any difference. > > Did anybody ever try modifying the freezer for suspend (not > > hibernate), so that it allows tasks not in running state to freeze? > > If not, I think that's an experiment worth doing. > > What happens if the reason the task isn't running is because it's > waiting for I/O to complete? I just don't think this can be made to > work. Don't know. I've never written a driver, and I'm not familiar with runtime PM, etc. So I can't come up with a detailed design for solving the freezer issues there. But I do think that the solution does not lie in "fixing" the VFS. Miklos _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
