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 X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DC312C5ACAE for ; Thu, 12 Sep 2019 08:16:06 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id AAD6B20650 for ; Thu, 12 Sep 2019 08:16:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AAD6B20650 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:59072 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8KGr-00089j-Rf for qemu-devel@archiver.kernel.org; Thu, 12 Sep 2019 04:16:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59478) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8KFE-0007Ot-BX for qemu-devel@nongnu.org; Thu, 12 Sep 2019 04:14:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i8KFD-0007yw-4N for qemu-devel@nongnu.org; Thu, 12 Sep 2019 04:14:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49540) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i8KFA-0007xb-7y; Thu, 12 Sep 2019 04:14:20 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 91FBA308212D; Thu, 12 Sep 2019 08:14:19 +0000 (UTC) Received: from linux.fritz.box (ovpn-116-179.ams2.redhat.com [10.36.116.179]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D9E425C22C; Thu, 12 Sep 2019 08:14:15 +0000 (UTC) Date: Thu, 12 Sep 2019 10:14:14 +0200 From: Kevin Wolf To: Eric Blake Message-ID: <20190912081414.GC5383@linux.fritz.box> References: <20190911161521.59261-1-slp@redhat.com> <6755b34b-b412-9e63-8d25-b7662d0d3860@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="CdrF4e02JqNVZeln" Content-Disposition: inline In-Reply-To: <6755b34b-b412-9e63-8d25-b7662d0d3860@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Thu, 12 Sep 2019 08:14:19 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH] nbd/server: attach client channel to the export's AioContext X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-block@nongnu.org, Sergio Lopez , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --CdrF4e02JqNVZeln Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Am 11.09.2019 um 23:33 hat Eric Blake geschrieben: > On 9/11/19 12:21 PM, Eric Blake wrote: > > On 9/11/19 11:15 AM, Sergio Lopez wrote: > >> On creation, the export's AioContext is set to the same one as the > >> BlockBackend, while the AioContext in the client QIOChannel is left > >> untouched. > >> > >> As a result, when using data-plane, nbd_client_receive_next_request() > >> schedules coroutines in the IOThread AioContext, while the client's > >> QIOChannel is serviced from the main_loop, potentially triggering the > >> assertion at qio_channel_restart_[read|write]. > >> > >> To fix this, as soon we have the export corresponding to the client, > >> we call qio_channel_attach_aio_context() to attach the QIOChannel > >> context to the export's AioContext. This matches with the logic in > >> blk_aio_attached(). > >> > >> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=3D1748253 > >> Signed-off-by: Sergio Lopez > >> --- > >> nbd/server.c | 2 ++ > >> 1 file changed, 2 insertions(+) > >=20 > > I'd like a second opinion from Kevin, but the description makes sense to > > me. I'm happy to queue this through my NBD tree. > >=20 > > Reviewed-by: Eric Blake >=20 > I tried to test this patch, but even with it applied, I still got an > aio-context crasher by attempting an nbd-server-start, nbd-server-add, > nbd-server-stop (intentionally skipping the nbd-server-remove step) on a > domain using iothreads, with a backtrace of: >=20 > #0 0x00007ff09d070e35 in raise () from target:/lib64/libc.so.6 > #1 0x00007ff09d05b895 in abort () from target:/lib64/libc.so.6 > #2 0x000055dd03b9ab86 in error_exit (err=3D1, msg=3D0x55dd03d59fb0 > <__func__.15769> "qemu_mutex_unlock_impl") > at util/qemu-thread-posix.c:36 > #3 0x000055dd03b9adcf in qemu_mutex_unlock_impl (mutex=3D0x55dd062d5090, > file=3D0x55dd03d59041 "util/async.c", > line=3D523) at util/qemu-thread-posix.c:96 > #4 0x000055dd03b93433 in aio_context_release (ctx=3D0x55dd062d5030) at > util/async.c:523 > #5 0x000055dd03ac421b in bdrv_do_drained_begin (bs=3D0x55dd0673a2d0, > recursive=3Dfalse, parent=3D0x0, > ignore_bds_parents=3Dfalse, poll=3Dtrue) at block/io.c:428 > #6 0x000055dd03ac4299 in bdrv_drained_begin (bs=3D0x55dd0673a2d0) at > block/io.c:434 > #7 0x000055dd03aafb54 in blk_drain (blk=3D0x55dd06a3ec40) at > block/block-backend.c:1605 > #8 0x000055dd03aae054 in blk_remove_bs (blk=3D0x55dd06a3ec40) at > block/block-backend.c:800 > #9 0x000055dd03aad54a in blk_delete (blk=3D0x55dd06a3ec40) at > block/block-backend.c:420 > #10 0x000055dd03aad7d6 in blk_unref (blk=3D0x55dd06a3ec40) at > block/block-backend.c:475 > #11 0x000055dd03aecb68 in nbd_export_put (exp=3D0x55dd0726f920) at > nbd/server.c:1666 > #12 0x000055dd03aec8fe in nbd_export_close (exp=3D0x55dd0726f920) at > nbd/server.c:1616 > #13 0x000055dd03aecbf1 in nbd_export_close_all () at nbd/server.c:1689 > #14 0x000055dd03748845 in qmp_nbd_server_stop (errp=3D0x7ffcdf3cb4e8) at > blockdev-nbd.c:233 > ... >=20 > Does that sound familiar to what you were seeing? Does it mean we > missed another spot where the context is set incorrectly? I think nbd_export_close_all() or one of the NBD functions called by it needs to take the AioContext lock of the associated BlockBackend. The crash is because AIO_POLL_WHILE() wants to temporarily drop the lock that we're not even holding. Kevin --CdrF4e02JqNVZeln Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBAgAGBQJdef5WAAoJEH8JsnLIjy/WVBMP/1D1nwj8h+D7JjWc+ES7VMrS t5OKJVbXqH6/wlH+9qu9X6O66g5HSM47zMlkUAuFVWUzgS8HDIRfK7M6pv40BK5R ZNNWUglNxQ9oKImeEtL4/ag09RLjUoDV6jpgMLcDYefze1wLU7TTm95FhXDJnhlv TJ+1PKeg8OcuiI1yTkDokASCz9h6Lsgm5XKPI7bLYa9jOAM8pBVJJCkN4B8S6SCT 1pmRx/oT+fjPzsk68SyGXFKzA33+OMYHLhKbvzvZteEHUUtjrezK5ESvZTzSVDEN aF2OAHmnBX52AgVBdQ0ZURUx4aLAA/p4s1kgUxAFNqGrkjCEYzM2PECW8Z5FfdJ5 kt5GSJs1b3v/m/8azttxzEHZ8g7J5QGATpOJEeTSzfcdlRL7RfTh2LgpY+8z3okc etOBP51k94h43sEyprryTzEyzoheP94mUNl8wwPiVo4cggmAHLYNI/s7mCOAyZ4i WYSBAWRT9hxFNQijjGVALOmHwmcipxs532OXRHxVuzqaeTnHGH1oJghqHdtdlt0e Gof5diGoVy0egvTiOO6EqYPsjFVdXSLE9YsDDYrJBnP+Ay59nPWFj1+xSQ4xHCkH omH9ZpmBS6h1eoiSE2xZoPa7te5XvKi3a7PTfFOl5cmiMgK35HTXGPaXvKIJWEKd 63CEyb28WkWhZTDcb5F9 =AL5q -----END PGP SIGNATURE----- --CdrF4e02JqNVZeln--