From 5261dd7b0106a88c9b323607136b1dfa1d7db689 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Sat, 3 Feb 2018 10:39:34 -0500 Subject: [PATCH] coroutine-lock: make qemu_co_enter_next thread-safe qemu_co_queue_next does not need to release and re-acquire the mutex, because the queued coroutine does not run immediately. However, this does not hold for qemu_co_enter_next. Now that qemu_co_queue_wait can synchronize (via QemuLockable) with code that is not running in coroutine context, it's important that code using qemu_co_enter_next can easily use a standardized locking idiom. First of all, qemu_co_enter_next must use aio_co_wake to restart the coroutine. Second, the function gains a second argument, a QemuLockable*, and the comments of qemu_co_queue_next and qemu_co_queue_restart_all are adjusted to clarify the difference. Signed-off-by: Paolo Bonzini Message-Id: <20180203153935.8056-5-pbonzini@redhat.com> Reviewed-by: Stefan Hajnoczi Reviewed-by: Fam Zheng Signed-off-by: Fam Zheng --- fsdev/qemu-fsdev-throttle.c | 4 ++-- include/qemu/coroutine.h | 19 +++++++++++++------ util/qemu-coroutine-lock.c | 10 ++++++++-- 3 files changed, 23 insertions(+), 10 deletions(-) diff --git a/fsdev/qemu-fsdev-throttle.c b/fsdev/qemu-fsdev-throttle.c index 49eebb5412..1dc07fbc12 100644 --- a/fsdev/qemu-fsdev-throttle.c +++ b/fsdev/qemu-fsdev-throttle.c @@ -20,13 +20,13 @@ static void fsdev_throttle_read_timer_cb(void *opaque) { FsThrottle *fst = opaque; - qemu_co_enter_next(&fst->throttled_reqs[false]); + qemu_co_enter_next(&fst->throttled_reqs[false], NULL); } static void fsdev_throttle_write_timer_cb(void *opaque) { FsThrottle *fst = opaque; - qemu_co_enter_next(&fst->throttled_reqs[true]); + qemu_co_enter_next(&fst->throttled_reqs[true], NULL); } void fsdev_throttle_parse_opts(QemuOpts *opts, FsThrottle *fst, Error **errp) diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h index 1e5f0957e6..6f8a487041 100644 --- a/include/qemu/coroutine.h +++ b/include/qemu/coroutine.h @@ -188,21 +188,28 @@ void qemu_co_queue_init(CoQueue *queue); void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock); /** - * Restarts the next coroutine in the CoQueue and removes it from the queue. - * - * Returns true if a coroutine was restarted, false if the queue is empty. + * Removes the next coroutine from the CoQueue, and wake it up. + * Returns true if a coroutine was removed, false if the queue is empty. */ bool coroutine_fn qemu_co_queue_next(CoQueue *queue); /** - * Restarts all coroutines in the CoQueue and leaves the queue empty. + * Empties the CoQueue; all coroutines are woken up. */ void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue); /** - * Enter the next coroutine in the queue + * Removes the next coroutine from the CoQueue, and wake it up. Unlike + * qemu_co_queue_next, this function releases the lock during aio_co_wake + * because it is meant to be used outside coroutine context; in that case, the + * coroutine is entered immediately, before qemu_co_enter_next returns. + * + * If used in coroutine context, qemu_co_enter_next is equivalent to + * qemu_co_queue_next. */ -bool qemu_co_enter_next(CoQueue *queue); +#define qemu_co_enter_next(queue, lock) \ + qemu_co_enter_next_impl(queue, QEMU_MAKE_LOCKABLE(lock)) +bool qemu_co_enter_next_impl(CoQueue *queue, QemuLockable *lock); /** * Checks if the CoQueue is empty. diff --git a/util/qemu-coroutine-lock.c b/util/qemu-coroutine-lock.c index 2a66fc1467..78fb79acf8 100644 --- a/util/qemu-coroutine-lock.c +++ b/util/qemu-coroutine-lock.c @@ -132,7 +132,7 @@ void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue) qemu_co_queue_do_restart(queue, false); } -bool qemu_co_enter_next(CoQueue *queue) +bool qemu_co_enter_next_impl(CoQueue *queue, QemuLockable *lock) { Coroutine *next; @@ -142,7 +142,13 @@ bool qemu_co_enter_next(CoQueue *queue) } QSIMPLEQ_REMOVE_HEAD(&queue->entries, co_queue_next); - qemu_coroutine_enter(next); + if (lock) { + qemu_lockable_unlock(lock); + } + aio_co_wake(next); + if (lock) { + qemu_lockable_lock(lock); + } return true; }