From 758e1b2b622d7c177dc2d95e887a11aa069b7e68 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 2 Sep 2016 23:33:38 +0200 Subject: cpus-common: simplify locking for start_exclusive/end_exclusive MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: Richard Henderson Reviewed-by: Alex Bennée Signed-off-by: Paolo Bonzini --- cpus-common.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) (limited to 'cpus-common.c') diff --git a/cpus-common.c b/cpus-common.c index 80aaf9b42d..429652c7fd 100644 --- a/cpus-common.c +++ b/cpus-common.c @@ -171,8 +171,7 @@ static inline void exclusive_idle(void) } /* Start an exclusive operation. - Must only be called from outside cpu_exec, takes - qemu_cpu_list_lock. */ + Must only be called from outside cpu_exec. */ void start_exclusive(void) { CPUState *other_cpu; @@ -191,11 +190,17 @@ void start_exclusive(void) while (pending_cpus > 1) { qemu_cond_wait(&exclusive_cond, &qemu_cpu_list_lock); } + + /* Can release mutex, no one will enter another exclusive + * section until end_exclusive resets pending_cpus to 0. + */ + qemu_mutex_unlock(&qemu_cpu_list_lock); } -/* Finish an exclusive operation. Releases qemu_cpu_list_lock. */ +/* Finish an exclusive operation. */ void end_exclusive(void) { + qemu_mutex_lock(&qemu_cpu_list_lock); pending_cpus = 0; qemu_cond_broadcast(&exclusive_resume); qemu_mutex_unlock(&qemu_cpu_list_lock); -- cgit v1.2.1