Il 13/06/2013 22:55, Liu Ping Fan ha scritto:
> BH will be used outside big lock, so introduce lock to protect it.
> Note that the lock only affects the writer and bh's callback does
> not take this extra lock.
>
> Signed-off-by: Liu Ping Fan <pingf...@linux.vnet.ibm.com>
> ---
> async.c | 10 +++++++++-
> include/block/aio.h | 2 ++
> 2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/async.c b/async.c
> index 90fe906..b1dcead 100644
> --- a/async.c
> +++ b/async.c
> @@ -47,8 +47,11 @@ QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void
> *opaque)
> bh->ctx = ctx;
> bh->cb = cb;
> bh->opaque = opaque;
> + qemu_mutex_lock(&ctx->bh_lock);
> bh->next = ctx->first_bh;
> + smp_wmb();
> ctx->first_bh = bh;
> + qemu_mutex_unlock(&ctx->bh_lock);
> return bh;
> }
>
> @@ -60,7 +63,9 @@ int aio_bh_poll(AioContext *ctx)
> ctx->walking_bh++;
>
> ret = 0;
> - for (bh = ctx->first_bh; bh; bh = next) {
> + bh = ctx->first_bh;
> + smp_rmb();
> + for (; bh; bh = next) {
> next = bh->next;
The read barrier in theory should go inside the loop. On the other
hand, it only needs to be a smp_read_barrier_depends().
Paolo
> if (!bh->deleted && bh->scheduled) {
> bh->scheduled = 0;
> @@ -75,6 +80,7 @@ int aio_bh_poll(AioContext *ctx)
>
> /* remove deleted bhs */
> if (!ctx->walking_bh) {
> + qemu_mutex_lock(&ctx->bh_lock);
> bhp = &ctx->first_bh;
> while (*bhp) {
> bh = *bhp;
> @@ -85,6 +91,7 @@ int aio_bh_poll(AioContext *ctx)
> bhp = &bh->next;
> }
> }
> + qemu_mutex_unlock(&ctx->bh_lock);
> }
>
> return ret;
> @@ -211,6 +218,7 @@ AioContext *aio_context_new(void)
> ctx = (AioContext *) g_source_new(&aio_source_funcs, sizeof(AioContext));
> ctx->pollfds = g_array_new(FALSE, FALSE, sizeof(GPollFD));
> ctx->thread_pool = NULL;
> + qemu_mutex_init(&ctx->bh_lock);
> event_notifier_init(&ctx->notifier, false);
> aio_set_event_notifier(ctx, &ctx->notifier,
> (EventNotifierHandler *)
> diff --git a/include/block/aio.h b/include/block/aio.h
> index 1836793..a65d16f 100644
> --- a/include/block/aio.h
> +++ b/include/block/aio.h
> @@ -17,6 +17,7 @@
> #include "qemu-common.h"
> #include "qemu/queue.h"
> #include "qemu/event_notifier.h"
> +#include "qemu/thread.h"
>
> typedef struct BlockDriverAIOCB BlockDriverAIOCB;
> typedef void BlockDriverCompletionFunc(void *opaque, int ret);
> @@ -53,6 +54,7 @@ typedef struct AioContext {
> */
> int walking_handlers;
>
> + QemuMutex bh_lock;
> /* Anchor of the list of Bottom Halves belonging to the context */
> struct QEMUBH *first_bh;
>
>
