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authorPeter Maydell <peter.maydell@linaro.org>2015-08-18 17:06:41 +0100
committerPeter Maydell <peter.maydell@linaro.org>2015-08-18 17:06:41 +0100
commit5452b6f61ae943aff5c13cdd65fb476efff636d3 (patch)
treeddb6d57c5215baac48cba38708c115b590b0bdb8 /util
parent6b324b3e5906fd9a9ce7f4f24decd1f1c7afde97 (diff)
parent9504c5445cb709415aea509954a922983925c2d3 (diff)
Merge remote-tracking branch 'remotes/bonzini/tags/for-upstream' into staging
* SCSI fixes from Stefan and Fam * vhost-scsi fix from Igor and Lu Lina * a build system fix from Daniel * two more multi-arch-related patches from Peter C. * TCG patches from myself and Sergey Fedorov * RCU improvement from Wen Congyang * a few more simple cleanups # gpg: Signature made Fri 14 Aug 2015 22:41:52 BST using RSA key ID 78C7AE83 # gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" # gpg: aka "Paolo Bonzini <pbonzini@redhat.com>" # gpg: WARNING: This key is not certified with sufficiently trusted signatures! # gpg: It is not certain that the signature belongs to the owner. # Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4 E2F7 7E15 100C CD36 69B1 # Subkey fingerprint: F133 3857 4B66 2389 866C 7682 BFFB D25F 78C7 AE83 * remotes/bonzini/tags/for-upstream: disas: Defeature print_target_address hw: fix mask for ColdFire UART command register scsi-generic: identify AIO callbacks more clearly scsi-disk: identify AIO callbacks more clearly scsi: create restart bottom half in the right AioContext configure: only add CONFIG_RDMA to config-host.h once qemu-nbd: remove unnecessary qemu_notify_event() vhost-scsi: Clarify vhost_virtqueue_mask argument exec: use macro ROUND_UP for alignment rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu() exec: drop cpu_can_do_io, just read cpu->can_do_io cpu_defs: Simplify CPUTLB padding logic cpu-exec: Do not invalidate original TB in cpu_exec_nocache() vhost/scsi: call vhost_dev_cleanup() at unrealize() time virtio-scsi-test: Add test case for tail unaligned WRITE SAME scsi-disk: Fix assertion failure on WRITE SAME tests: virtio-scsi: clear unit attention after reset scsi-disk: fix cmd.mode field typo virtio-scsi: use virtqueue_map_sg() when loading requests Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Diffstat (limited to 'util')
-rw-r--r--util/rcu.c48
1 files changed, 35 insertions, 13 deletions
diff --git a/util/rcu.c b/util/rcu.c
index cdcad678b4..8ba304dc44 100644
--- a/util/rcu.c
+++ b/util/rcu.c
@@ -47,7 +47,8 @@
unsigned long rcu_gp_ctr = RCU_GP_LOCKED;
QemuEvent rcu_gp_event;
-static QemuMutex rcu_gp_lock;
+static QemuMutex rcu_registry_lock;
+static QemuMutex rcu_sync_lock;
/*
* Check whether a quiescent state was crossed between the beginning of
@@ -66,7 +67,7 @@ static inline int rcu_gp_ongoing(unsigned long *ctr)
*/
__thread struct rcu_reader_data rcu_reader;
-/* Protected by rcu_gp_lock. */
+/* Protected by rcu_registry_lock. */
typedef QLIST_HEAD(, rcu_reader_data) ThreadList;
static ThreadList registry = QLIST_HEAD_INITIALIZER(registry);
@@ -114,10 +115,26 @@ static void wait_for_readers(void)
break;
}
- /* Wait for one thread to report a quiescent state and
- * try again.
+ /* Wait for one thread to report a quiescent state and try again.
+ * Release rcu_registry_lock, so rcu_(un)register_thread() doesn't
+ * wait too much time.
+ *
+ * rcu_register_thread() may add nodes to &registry; it will not
+ * wake up synchronize_rcu, but that is okay because at least another
+ * thread must exit its RCU read-side critical section before
+ * synchronize_rcu is done. The next iteration of the loop will
+ * move the new thread's rcu_reader from &registry to &qsreaders,
+ * because rcu_gp_ongoing() will return false.
+ *
+ * rcu_unregister_thread() may remove nodes from &qsreaders instead
+ * of &registry if it runs during qemu_event_wait. That's okay;
+ * the node then will not be added back to &registry by QLIST_SWAP
+ * below. The invariant is that the node is part of one list when
+ * rcu_registry_lock is released.
*/
+ qemu_mutex_unlock(&rcu_registry_lock);
qemu_event_wait(&rcu_gp_event);
+ qemu_mutex_lock(&rcu_registry_lock);
}
/* put back the reader list in the registry */
@@ -126,7 +143,8 @@ static void wait_for_readers(void)
void synchronize_rcu(void)
{
- qemu_mutex_lock(&rcu_gp_lock);
+ qemu_mutex_lock(&rcu_sync_lock);
+ qemu_mutex_lock(&rcu_registry_lock);
if (!QLIST_EMPTY(&registry)) {
/* In either case, the atomic_mb_set below blocks stores that free
@@ -149,7 +167,8 @@ void synchronize_rcu(void)
wait_for_readers();
}
- qemu_mutex_unlock(&rcu_gp_lock);
+ qemu_mutex_unlock(&rcu_registry_lock);
+ qemu_mutex_unlock(&rcu_sync_lock);
}
@@ -273,23 +292,24 @@ void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node))
void rcu_register_thread(void)
{
assert(rcu_reader.ctr == 0);
- qemu_mutex_lock(&rcu_gp_lock);
+ qemu_mutex_lock(&rcu_registry_lock);
QLIST_INSERT_HEAD(&registry, &rcu_reader, node);
- qemu_mutex_unlock(&rcu_gp_lock);
+ qemu_mutex_unlock(&rcu_registry_lock);
}
void rcu_unregister_thread(void)
{
- qemu_mutex_lock(&rcu_gp_lock);
+ qemu_mutex_lock(&rcu_registry_lock);
QLIST_REMOVE(&rcu_reader, node);
- qemu_mutex_unlock(&rcu_gp_lock);
+ qemu_mutex_unlock(&rcu_registry_lock);
}
static void rcu_init_complete(void)
{
QemuThread thread;
- qemu_mutex_init(&rcu_gp_lock);
+ qemu_mutex_init(&rcu_registry_lock);
+ qemu_mutex_init(&rcu_sync_lock);
qemu_event_init(&rcu_gp_event, true);
qemu_event_init(&rcu_call_ready_event, false);
@@ -306,12 +326,14 @@ static void rcu_init_complete(void)
#ifdef CONFIG_POSIX
static void rcu_init_lock(void)
{
- qemu_mutex_lock(&rcu_gp_lock);
+ qemu_mutex_lock(&rcu_sync_lock);
+ qemu_mutex_lock(&rcu_registry_lock);
}
static void rcu_init_unlock(void)
{
- qemu_mutex_unlock(&rcu_gp_lock);
+ qemu_mutex_unlock(&rcu_registry_lock);
+ qemu_mutex_unlock(&rcu_sync_lock);
}
#endif