From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9428BC61DA4 for ; Thu, 9 Feb 2023 17:32:43 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pQAlp-0000r5-5k; Thu, 09 Feb 2023 12:31:41 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pQAln-0000qp-L2 for qemu-devel@nongnu.org; Thu, 09 Feb 2023 12:31:39 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pQAll-0002sV-Ta for qemu-devel@nongnu.org; Thu, 09 Feb 2023 12:31:39 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675963896; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=8XW37cEQie/Vhgzf43OavzT2dkUBsoOwlL+k9GTIkvo=; b=T1YYzEjPV59JDBHEnA6dziNZfh8W/oeziQgYEAqSocHbalVdgu+N+MMQFen/whqnUL3nIJ 8VSANHDRvDDSZW8mztCZGxglWsn0pTgdnIMEbDJRTYt6C+0yP7/jx606LJNhwsFfI+7Uv3 YTJjSogr4TfMFsl87szvHXWHcX2t7g8= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-392-_wHWCHGJPnCoC_Hnc_00og-1; Thu, 09 Feb 2023 12:31:34 -0500 X-MC-Unique: _wHWCHGJPnCoC_Hnc_00og-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6EA8F80280C; Thu, 9 Feb 2023 17:31:34 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.192]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 322F351FF; Thu, 9 Feb 2023 17:31:32 +0000 (UTC) Date: Thu, 9 Feb 2023 18:31:31 +0100 From: Kevin Wolf To: Emanuele Giuseppe Esposito Cc: qemu-block@nongnu.org, Hanna Reitz , Ninad Palsule , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , qemu-devel@nongnu.org Subject: Re: [PATCH] block/file-posix: don't use functions calling AIO_WAIT_WHILE in worker threads Message-ID: References: <20230209154522.1164401-1-eesposit@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230209154522.1164401-1-eesposit@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 09.02.2023 um 16:45 hat Emanuele Giuseppe Esposito geschrieben: > When calling bdrv_getlength() in handle_aiocb_write_zeroes(), the > function creates a new coroutine and then waits that it finishes using > AIO_WAIT_WHILE. > The problem is that this function could also run in a worker thread, > that has a different AioContext from main loop and iothreads, therefore > in AIO_WAIT_WHILE we will have in_aio_context_home_thread(ctx) == false > and therefore > assert(qemu_get_current_aio_context() == qemu_get_aio_context()); > in the else branch will fail, crashing QEMU. > > Aside from that, bdrv_getlength() is wrong also conceptually, because > it reads the BDS graph from another thread and is not protected by > any lock. > > Replace it with raw_co_getlength, that doesn't create a coroutine and > doesn't read the BDS graph. > > Signed-off-by: Emanuele Giuseppe Esposito > --- > block/file-posix.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/file-posix.c b/block/file-posix.c > index d3073a7caa..9a99111f45 100644 > --- a/block/file-posix.c > +++ b/block/file-posix.c > @@ -1738,7 +1738,7 @@ static int handle_aiocb_write_zeroes(void *opaque) > #ifdef CONFIG_FALLOCATE > /* Last resort: we are trying to extend the file with zeroed data. This > * can be done via fallocate(fd, 0) */ > - len = bdrv_getlength(aiocb->bs); > + len = raw_co_getlength(aiocb->bs); > if (s->has_fallocate && len >= 0 && aiocb->aio_offset >= len) { > int ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes); > if (ret == 0 || ret != -ENOTSUP) { Obviously this relies on the fact that raw_co_getlength() doesn't actually depend on running in coroutine context. Could be done in a separate patch, but I think we should rename it back to raw_getlength() and remove the coroutine_fn annotation again. Seems commit c86422c5549 was a little too eager. Kevin