On 30/11/2016 14:31, Stefan Hajnoczi wrote: > 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()?
It could use atomic_read there, indeed. Paolo
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