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| author | Paolo Bonzini <pbonzini@redhat.com> | 2016-09-02 23:33:38 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2016-09-27 11:57:30 +0200 |
| commit | 758e1b2b622d7c177dc2d95e887a11aa069b7e68 (patch) | |
| tree | 4b8fc6e2fa1fac81eeb8d038ee1f213dbab71a3a | |
| parent | cf07da65f335b9a74e62f5413078f67280572f36 (diff) | |
| download | qemu-758e1b2b622d7c177dc2d95e887a11aa069b7e68.zip | |
cpus-common: simplify locking for start_exclusive/end_exclusive
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 <rth@twiddle.net>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | cpus-common.c | 11 | ||||
| -rw-r--r-- | docs/tcg-exclusive.promela | 4 | ||||
| -rw-r--r-- | include/qom/cpu.h | 4 |
3 files changed, 11 insertions, 8 deletions
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); diff --git a/docs/tcg-exclusive.promela b/docs/tcg-exclusive.promela index 8bb0967df6..feac679b9a 100644 --- a/docs/tcg-exclusive.promela +++ b/docs/tcg-exclusive.promela @@ -98,9 +98,11 @@ 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 f8726140f6..934c07afbf 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); |