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[[!tag open_issue_tmpfs]]

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.  We'd need 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.