If QEMU forks after the CPU threads have been created, qemu_mutex_lock_iothread
will not be able to do qemu_cpu_kick_thread. There is no solution other than
assuming that forks after the CPU threads have been created will end up in an
exec. Forks before the CPU threads have been created (such as -daemonize)
have to call rcu_after_fork manually.
Notably, the oxygen theme for GTK+ forks and shows a "No such process" error
without this patch.
This patch can be reverted once the iothread loses the "kick the TCG thread"
magic.
User-mode emulation does not use the iothread, so it can also call
rcu_after_fork.
Reported by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
After forking, only the calling thread is duplicated in the child process.
The call_rcu thread has to be recreated in the child. Exploit the fact
that only one thread exists (same as when constructors run), and just redo
the entire initialization to ensure the threads are in the proper state.
The only additional things to do are emptying the list of threads
registered with RCU, and unlocking the lock that was taken in the prepare
callback (implementations are allowed to fail pthread_mutex_init()
if the mutex is still locked).
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This needs to go away sooner or later, but one complication is the
complex VFIO data structures that are modified in instance_finalize.
Take a shortcut for now.
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Always process them within a short time. Even though waiting a little
is useful, it is not okay to delay e.g. qemu_opts_del forever.
Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Asynchronous callbacks provided by call_rcu are particularly important
for QEMU, because the BQL makes it hard to use synchronize_rcu.
In addition, the current RCU implementation is not particularly friendly
to multiple concurrent synchronize_rcu callers, making call_rcu even
more important.
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This includes a (mangled) copy of the liburcu code. The main changes
are: 1) removing dependencies on many other header files in liburcu; 2)
removing for simplicity the tentative busy waiting in synchronize_rcu,
which has limited performance effects; 3) replacing futexes in
synchronize_rcu with QemuEvents for Win32 portability. The API is
the same as liburcu, so it should be possible in the future to require
liburcu on POSIX systems for example and use our copy only on Windows.
Among the various versions available I chose urcu-mb, which is the
least invasive implementation even though it does not have the
fastest rcu_read_{lock,unlock} implementation. The urcu flavor can
be changed later, after benchmarking.
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
