Developer documentation should be its own manual.  As a start, move all
developer-oriented files to a separate directory.

Also move non-text files to their own directories: docs/config/ for
QEMU -readconfig input, and docs/spin/ for formal models to be used
with the SPIN model checker.
Reviewed-by: NDaniel P. Berrange <berrange@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Set cpu->running without taking the cpu_list lock, only requiring it if
there is a concurrent exclusive section.  This requires adding a new
field to CPUState, which records whether a running CPU is being counted
in pending_cpus.

When an exclusive section is started concurrently with cpu_exec_start,
cpu_exec_start can use the new field to determine if it has to wait for
the end of the exclusive section.  Likewise, cpu_exec_end can use it to
see if start_exclusive is waiting for that CPU.

This a separate patch for easier bisection of issues.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

It is not necessary to hold qemu_cpu_list_mutex throughout the
exclusive section, because no other exclusive section can run
while pending_cpus != 0.

exclusive_idle() is called in cpu_exec_start(), and that prevents
any CPUs created after start_exclusive() from entering cpu_exec()
during an exclusive section.
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

No need to call exclusive_idle() from cpu_exec_end since it is done
immediately afterwards in cpu_exec_start.  Any exclusive section could
run as soon as cpu_exec_end leaves, because cpu->running is false and the
mutex is not taken, so the call does not add any protection either.
Reviewed-by: NRichard Henderson <rth@twiddle.net>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

Reviewed-by: NRichard Henderson <rth@twiddle.net>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>