On Tue, Nov 29, 2016 at 12:47:03PM +0100, Paolo Bonzini wrote:
> @@ -272,22 +275,32 @@ bool aio_prepare(AioContext *ctx)
> bool aio_pending(AioContext *ctx)
> {
> AioHandler *node;
> + bool result = false;
>
> - QLIST_FOREACH(node, &ctx->aio_handlers, node) {
> + /*
> + * We have to walk very carefully in case aio_set_fd_handler is
> + * called while we're walking.
> + */
> + qemu_lockcnt_inc(&ctx->list_lock);
> +
> + QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {
> int revents;
>
> revents = node->pfd.revents & node->pfd.events;
> if (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR) && node->io_read &&
> aio_node_check(ctx, node->is_external)) {
> - return true;
> + result = true;
> + break;
> }
> if (revents & (G_IO_OUT | G_IO_ERR) && node->io_write &&
> aio_node_check(ctx, node->is_external)) {
> - return true;
> + result = true;
> + break;
> }
> }
> + qemu_lockcnt_dec(&ctx->list_lock);
>
> - return false;
> + return result;
> }
>
> bool aio_dispatch(AioContext *ctx)
> @@ -308,13 +321,12 @@ bool aio_dispatch(AioContext *ctx)
> * We have to walk very carefully in case aio_set_fd_handler is
> * called while we're walking.
> */
> - ctx->walking_handlers++;
> + qemu_lockcnt_inc(&ctx->list_lock);
>
> - QLIST_FOREACH_SAFE(node, &ctx->aio_handlers, node, tmp) {
> + QLIST_FOREACH_SAFE_RCU(node, &ctx->aio_handlers, node, tmp) {
> int revents;
>
> - revents = node->pfd.revents & node->pfd.events;
> - node->pfd.revents = 0;
> + revents = atomic_xchg(&node->pfd.revents, 0) & node->pfd.events;Why is node->pfd.revents accessed with atomic_*() here and in aio_poll() but not in aio_pending()?
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