| Message ID | 1474615909-17069-14-git-send-email-pbonzini@redhat.com |
|---|---|
| State | New |
| Headers | show |
On 09/23/2016 12:31 AM, Paolo Bonzini wrote: > 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. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > --- > cpus-common.c | 11 ++++++++--- > docs/tcg-exclusive.promela | 4 +++- > include/qom/cpu.h | 4 ---- > 3 files changed, 11 insertions(+), 8 deletions(-) Reviewed-by: Richard Henderson <rth@twiddle.net> r~
Paolo Bonzini <pbonzini@redhat.com> writes: > 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. > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> > --- > cpus-common.c | 11 ++++++++--- > docs/tcg-exclusive.promela | 4 +++- > include/qom/cpu.h | 4 ---- > 3 files changed, 11 insertions(+), 8 deletions(-) > > diff --git a/cpus-common.c b/cpus-common.c > index 80aaf9b..429652c 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); > diff --git a/docs/tcg-exclusive.promela b/docs/tcg-exclusive.promela > index 9e7d9e3..a8896e5 100644 > --- a/docs/tcg-exclusive.promela > +++ b/docs/tcg-exclusive.promela > @@ -97,9 +97,11 @@ byte has_waiter[N_CPUS]; > do \ > :: pending_cpus > 1 -> COND_WAIT(exclusive_cond, mutex); \ > :: else -> break; \ > - od > + od; \ > + MUTEX_UNLOCK(mutex); > > #define end_exclusive() \ > + MUTEX_LOCK(mutex); \ > pending_cpus = 0; \ > COND_BROADCAST(exclusive_resume); \ > MUTEX_UNLOCK(mutex); > diff --git a/include/qom/cpu.h b/include/qom/cpu.h > index f872614..934c07a 100644 > --- a/include/qom/cpu.h > +++ b/include/qom/cpu.h > @@ -846,9 +846,6 @@ void cpu_exec_end(CPUState *cpu); > * cpu_exec are exited immediately. CPUs that call cpu_exec_start > * during the exclusive section go to sleep until this CPU calls > * end_exclusive. > - * > - * Returns with the CPU list lock taken (which nests outside all > - * other locks except the BQL). > */ > void start_exclusive(void); > > @@ -856,7 +853,6 @@ void start_exclusive(void); > * end_exclusive: > * > * Concludes an exclusive execution section started by start_exclusive. > - * Releases the CPU list lock. > */ > void end_exclusive(void); -- Alex Bennée
diff --git a/cpus-common.c b/cpus-common.c index 80aaf9b..429652c 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); diff --git a/docs/tcg-exclusive.promela b/docs/tcg-exclusive.promela index 9e7d9e3..a8896e5 100644 --- a/docs/tcg-exclusive.promela +++ b/docs/tcg-exclusive.promela @@ -97,9 +97,11 @@ byte has_waiter[N_CPUS]; do \ :: pending_cpus > 1 -> COND_WAIT(exclusive_cond, mutex); \ :: else -> break; \ - od + od; \ + MUTEX_UNLOCK(mutex); #define end_exclusive() \ + MUTEX_LOCK(mutex); \ pending_cpus = 0; \ COND_BROADCAST(exclusive_resume); \ MUTEX_UNLOCK(mutex); diff --git a/include/qom/cpu.h b/include/qom/cpu.h index f872614..934c07a 100644 --- a/include/qom/cpu.h +++ b/include/qom/cpu.h @@ -846,9 +846,6 @@ void cpu_exec_end(CPUState *cpu); * cpu_exec are exited immediately. CPUs that call cpu_exec_start * during the exclusive section go to sleep until this CPU calls * end_exclusive. - * - * Returns with the CPU list lock taken (which nests outside all - * other locks except the BQL). */ void start_exclusive(void); @@ -856,7 +853,6 @@ void start_exclusive(void); * end_exclusive: * * Concludes an exclusive execution section started by start_exclusive. - * Releases the CPU list lock. */ void end_exclusive(void);
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. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- cpus-common.c | 11 ++++++++--- docs/tcg-exclusive.promela | 4 +++- include/qom/cpu.h | 4 ---- 3 files changed, 11 insertions(+), 8 deletions(-)