On Thu, Dec 19, 2024 at 06:42:09PM +0100, Paolo Bonzini wrote: > On 12/19/24 18:32, Keith Busch wrote: > > This appears to be causing a user space regression. The library > > "minijail" is used by virtual machine manager "crossvm". crossvm uses > > minijail to fork processes, but the library requires the process be > > single threaded. Prior to this patch, the process was single threaded, > > but this change creates a relationship from the kvm thread to the user > > process that fails minijail's test. > > Thanks for the report. > > The minijail code has a flag that's documented like this: > > /// Disables the check that prevents forking in a multithreaded environment. > /// This is only safe if the child process calls exec immediately after > /// forking. The state of locks, and whether or not they will unlock > /// is undefined. Additionally, objects allocated on other threads that > /// expect to be dropped when those threads cease execution will not be > /// dropped. > /// Thus, nothing should be called that relies on shared synchronization > /// primitives referenced outside of the current thread. The safest > /// way to use this is to immediately exec in the child. > > Is crosvm trying to do anything but exec? If not, it should probably use the > flag. Good point, and I'm not sure right now. I don't think I know any crosvm developer experts but I'm working on that to get a better explanation of what's happening,
