On 11/04/2018 18:39, Kevin Wolf wrote:
> bdrv_drain_all() wants to have a single polling loop for draining the
> in-flight requests of all nodes. This means that the AIO_WAIT_WHILE()
> condition relies on activity in multiple AioContexts, which is polled
> from the mainloop context. We must therefore call AIO_WAIT_WHILE() from
> the mainloop thread and use the AioWait notification mechanism.
>
> Just randomly picking the AioContext of any non-mainloop thread would
> work, but instead of bothering to find such a context in the caller, we
> can just as well accept NULL for ctx.
>
> Signed-off-by: Kevin Wolf <kw...@redhat.com>
> ---
> include/block/aio-wait.h | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/include/block/aio-wait.h b/include/block/aio-wait.h
> index 783d3678dd..c85a62f798 100644
> --- a/include/block/aio-wait.h
> +++ b/include/block/aio-wait.h
> @@ -57,7 +57,8 @@ typedef struct {
> /**
> * AIO_WAIT_WHILE:
> * @wait: the aio wait object
> - * @ctx: the aio context
> + * @ctx: the aio context, or NULL if multiple aio contexts (for which the
> + * caller does not hold a lock) are involved in the polling condition.
> * @cond: wait while this conditional expression is true
> *
> * Wait while a condition is true. Use this to implement synchronous
> @@ -75,7 +76,7 @@ typedef struct {
> bool waited_ = false; \
> AioWait *wait_ = (wait); \
> AioContext *ctx_ = (ctx); \
> - if (in_aio_context_home_thread(ctx_)) { \
> + if (ctx_ && in_aio_context_home_thread(ctx_)) { \
> while ((cond)) { \
> aio_poll(ctx_, true); \
> waited_ = true; \
> @@ -86,9 +87,13 @@ typedef struct {
> /* Increment wait_->num_waiters before evaluating cond. */ \
> atomic_inc(&wait_->num_waiters); \
> while ((cond)) { \
> - aio_context_release(ctx_); \
> + if (ctx_) { \
> + aio_context_release(ctx_); \
> + } \
> aio_poll(qemu_get_aio_context(), true); \
> - aio_context_acquire(ctx_); \
> + if (ctx_) { \
> + aio_context_acquire(ctx_); \
> + } \
> waited_ = true; \
> } \
> atomic_dec(&wait_->num_waiters); \
>
Looks good.
Paolo
