> > > > > I have discussed the benefits elsewhere. As for the deadlocks -- do > > > > > you still observe them if you use the version of the freezer which > > > > > doesn't freeze kernel threads? > > > > > > > > In general the only way to guarantee there are no deadlocks is to > > > > construct the graph of dependencies between tasks. Those dependencies > > > > are not in practice observable from outside the tasks, so it is > > > > virtually impossible to construct the graph. > > > > > > In which way can user space tasks depend on each other in a way that > > > allows a them members of that cycle to be in uninterruptible sleep? > > > > - process A calls rename() on a fuse fs > > - process B, the fuse server, starts to process the rename request > > - process B is frozen before it can reply > > > > Now process A is unfreezable. We cannot make rename() restartable, > > hence it cannot be interruptible. > > Yes, we are claiming fuse is very special in this regard, and perhaps > even broken. > > Let's see. If I SIGSTOP the fuse server, I can get unrelated tasks > unkillable (even for SIGKILL!) forever. Actually fuse allows SIGKILL, because it's always fatal, and the syscall may not be restarted. > That's very special, and maybe even a FUSE bug. And that is also > what makes FUSE special w.r.t. s2ram. What makes fuse special is that some file operations are synchronous and non-restartable. That's just how the UNIX filesystem API works and is hardly a bug in fuse. > So no, you can't claim "FUSE is just IPC". It is very special IPC. I did say it's special. Sure, it has some "interesting" properties, and with a bit of malice you can do very ugly things with it. If you are interested, read Documentation/filesystems/fuse.txt, especially the "Tricky deadlock" section ;) Miklos _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
