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[Qemu-devel] [PULL 22/28] cpus-common: simplify locking for start_exclus
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 22/28] cpus-common: simplify locking for start_exclusive/end_exclusive |
Date: |
Mon, 26 Sep 2016 15:40:52 +0200 |
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 <address@hidden>
Reviewed-by: Alex Bennée <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
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 8bb0967..feac679 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 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);
--
2.7.4
- [Qemu-devel] [PULL 12/28] cpus: Rename flush_queued_work(), (continued)
- [Qemu-devel] [PULL 12/28] cpus: Rename flush_queued_work(), Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 11/28] cpus: Move common code out of {async_, }run_on_cpu(), Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 13/28] linux-user: Use QemuMutex and QemuCond, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 14/28] linux-user: Add qemu_cpu_is_self() and qemu_cpu_kick(), Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 15/28] cpus-common: move CPU list management to common code, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 17/28] cpus-common: fix uninitialized variable use in run_on_cpu, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 16/28] cpus-common: move CPU work item management to common code, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 19/28] docs: include formal model for TCG exclusive sections, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 20/28] cpus-common: always defer async_run_on_cpu work items, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 21/28] cpus-common: remove redundant call to exclusive_idle(), Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 22/28] cpus-common: simplify locking for start_exclusive/end_exclusive,
Paolo Bonzini <=
- [Qemu-devel] [PULL 18/28] cpus-common: move exclusive work infrastructure from linux-user, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 23/28] cpus-common: Introduce async_safe_run_on_cpu(), Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 25/28] cpus-common: lock-free fast path for cpu_exec_start/end, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 24/28] tcg: Make tb_flush() thread safe, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 26/28] replay: move internal data to the structure, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 28/28] replay: allow replay stopping and restarting, Paolo Bonzini, 2016/09/26
- [Qemu-devel] [PULL 27/28] replay: vmstate for replay module, Paolo Bonzini, 2016/09/26
- Re: [Qemu-devel] [PULL 00/28] Misc patches for 2016-09-26, no-reply, 2016/09/26
- Re: [Qemu-devel] [PULL 00/28] Misc patches for 2016-09-26, Peter Maydell, 2016/09/26