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[Qemu-devel] [PATCH 15/16] aio: document locking
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 15/16] aio: document locking |
Date: |
Mon, 8 Feb 2016 17:15:06 +0100 |
Signed-off-by: Paolo Bonzini <address@hidden>
---
docs/multiple-iothreads.txt | 5 ++---
include/block/aio.h | 32 ++++++++++++++++----------------
2 files changed, 18 insertions(+), 19 deletions(-)
diff --git a/docs/multiple-iothreads.txt b/docs/multiple-iothreads.txt
index c5d38e9..8ec3777 100644
--- a/docs/multiple-iothreads.txt
+++ b/docs/multiple-iothreads.txt
@@ -84,9 +84,8 @@ How to synchronize with an IOThread
AioContext is not thread-safe so some rules must be followed when using file
descriptors, event notifiers, timers, or BHs across threads:
-1. AioContext functions can be called safely from file descriptor, event
-notifier, timer, or BH callbacks invoked by the AioContext. No locking is
-necessary.
+1. AioContext functions can always be called safely. They handle their
+own locking internally.
2. Other threads wishing to access the AioContext must take the QEMU global
mutex *as well as* call aio_context_acquire()/aio_context_release() for
diff --git a/include/block/aio.h b/include/block/aio.h
index fb0ff21..cea92b0 100644
--- a/include/block/aio.h
+++ b/include/block/aio.h
@@ -50,18 +50,12 @@ typedef void IOHandler(void *opaque);
struct AioContext {
GSource source;
- /* Protects all fields from multi-threaded access */
+ /* Used by AioContext users to protect from multi-threaded access. */
QemuRecMutex lock;
- /* The list of registered AIO handlers */
+ /* The list of registered AIO handlers. Protected by ctx->list_lock. */
QLIST_HEAD(, AioHandler) aio_handlers;
- /* This is a simple lock used to protect the aio_handlers list.
- * Specifically, it's used to ensure that no callbacks are removed while
- * we're walking and dispatching callbacks.
- */
- int walking_handlers;
-
/* Used to avoid unnecessary event_notifier_set calls in aio_notify;
* accessed with atomic primitives. If this field is 0, everything
* (file descriptors, bottom halves, timers) will be re-evaluated
@@ -87,9 +81,9 @@ struct AioContext {
*/
uint32_t notify_me;
- /* A lock to protect between bh's adders and deleter, and to ensure
- * that no callbacks are removed while we're walking and dispatching
- * them.
+ /* A lock to protect between QEMUBH and AioHandler adders and deleter,
+ * and to ensure that no callbacks are removed while we're walking and
+ * dispatching them.
*/
QemuLockCnt list_lock;
@@ -111,10 +105,14 @@ struct AioContext {
bool notified;
EventNotifier notifier;
- /* Thread pool for performing work and receiving completion callbacks */
+ /* Thread pool for performing work and receiving completion callbacks.
+ * Has its own locking.
+ */
struct ThreadPool *thread_pool;
- /* TimerLists for calling timers - one per clock type */
+ /* TimerLists for calling timers - one per clock type. Has its own
+ * locking.
+ */
QEMUTimerListGroup tlg;
int external_disable_cnt;
@@ -162,9 +160,11 @@ void aio_context_unref(AioContext *ctx);
* automatically takes care of calling aio_context_acquire and
* aio_context_release.
*
- * Access to timers and BHs from a thread that has not acquired AioContext
- * is possible. Access to callbacks for now must be done while the AioContext
- * is owned by the thread (FIXME).
+ * Note that this is separate from bdrv_drained_begin/bdrv_drained_end. A
+ * thread still has to call those to avoid being interrupted by the guest.
+ *
+ * Bottom halves, timers and callbacks can be created or removed without
+ * acquiring the AioContext.
*/
void aio_context_acquire(AioContext *ctx);
--
2.5.0
- [Qemu-devel] [PATCH 04/16] aio: only call aio_poll_internal from iothread, (continued)
- [Qemu-devel] [PATCH 04/16] aio: only call aio_poll_internal from iothread, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 12/16] aio: tweak walking in dispatch phase, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 11/16] qemu-thread: optimize QemuLockCnt with futexes on Linux, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 14/16] aio-win32: remove walking_handlers, protecting AioHandler list with list_lock, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 13/16] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 10/16] aio: make ctx->list_lock a QemuLockCnt, subsuming ctx->walking_bh, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 16/16] aio: push aio_context_acquire/release down to dispatching, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 15/16] aio: document locking,
Paolo Bonzini <=