On Sat, Feb 28, 2015 at 12:22:47PM +0100, Samuel Thibault wrote: > For instance the X server crashes on fvwm startup, or mupdf crashes, > when /run is served by a tmpfs. > > What happens is that they create an shm (shmget, thus a file in > /run/shm/, backed by tmpfs), then map it (shmat, i.e. open/mmap/close of > the file), then remove access to it (shmctl(IPC_RMID), i.e. unlink the > file). > > The issue is that even if the file is still mapped, unlinking it from > tmpfs makes tmpfs mach_port_deallocate the memobj, which apparently > drops the object completely, and subsequent accesses to the mmap thus > fail with SIGBUS. Would there be a way for tmpfs to know about the > mappings of the pager object, to avoid shutting it down? Or a way to > keep the object alive even if tmpfs has deallocated its port to it? > I don't know memory management enough to answer it.
I'd say that glibc (in mmap) should add a reference to the file. On munmap or process termination, all references are dropped. -- Richard Braun
