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spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:47278 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mLTdm-0002vf-04 for qemu-devel@archiver.kernel.org; Wed, 01 Sep 2021 13:03:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41846) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mLTOe-0000RZ-2P for qemu-devel@nongnu.org; Wed, 01 Sep 2021 12:47:32 -0400 Received: from us-smtp-delivery-44.mimecast.com ([205.139.111.44]:46941) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mLTOc-00019B-5R for qemu-devel@nongnu.org; Wed, 01 Sep 2021 12:47:31 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-596-PkbgyiaXPDi3CmwN2ZdlzA-1; Wed, 01 Sep 2021 12:47:24 -0400 X-MC-Unique: PkbgyiaXPDi3CmwN2ZdlzA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 0869487D544; Wed, 1 Sep 2021 16:47:24 +0000 (UTC) Received: from bahia.lan (unknown [10.39.192.57]) by smtp.corp.redhat.com (Postfix) with ESMTP id 20D37100238C; Wed, 1 Sep 2021 16:47:22 +0000 (UTC) Date: Wed, 1 Sep 2021 18:47:21 +0200 From: Greg Kurz To: Christian Schoenebeck Subject: Re: [SPAM] [PATCH] 9pfs: fix crash in v9fs_walk() Message-ID: <20210901184721.57b1f611@bahia.lan> In-Reply-To: References: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=groug@kaod.org X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kaod.org Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Received-SPF: softfail client-ip=205.139.111.44; envelope-from=groug@kaod.org; helo=us-smtp-delivery-44.mimecast.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_SOFTFAIL=0.665 autolearn=no autolearn_force=no X-Spam_action: no action 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-devel@nongnu.org, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 1 Sep 2021 18:15:10 +0200 Christian Schoenebeck wrote: > v9fs_walk() utilizes the v9fs_co_run_in_worker({...}) macro to run the > supplied fs driver code block on a background worker thread. >=20 > When either the 'Twalk' client request was interrupted or if the client > requested fid for that 'Twalk' request caused a stat error then that > fs driver code block was left by 'break' keyword, with the intention to > return from worker thread back to main thread as well: >=20 > v9fs_co_run_in_worker({ > if (v9fs_request_cancelled(pdu)) { > err =3D -EINTR; > break; > } > err =3D s->ops->lstat(&s->ctx, &dpath, &fidst); > if (err < 0) { > err =3D -errno; > break; > } > ... > }); >=20 > However that 'break;' statement also skipped the v9fs_co_run_in_worker() > macro's final and mandatory >=20 > /* re-enter back to qemu thread */ > qemu_coroutine_yield(); >=20 > call and thus caused the rest of v9fs_walk() to be continued being > executed on the worker thread instead of main thread, eventually > leading to a crash in the transport virtio transport driver. >=20 > To fix this issue and to prevent the same error from happening again by > other users of v9fs_co_run_in_worker() in future, auto wrap the supplied > code block into its own >=20 > do { } while (0); >=20 > loop inside the 'v9fs_co_run_in_worker' macro definition. >=20 > Full discussion and backtrace: > https://lists.gnu.org/archive/html/qemu-devel/2021-08/msg05209.html > https://lists.gnu.org/archive/html/qemu-devel/2021-09/msg00174.html >=20 > Fixes: 8d6cb100731c4d28535adbf2a3c2d1f29be3fef4 > Signed-off-by: Christian Schoenebeck > Cc: qemu-stable@nongnu.org > --- Reviewed-by: Greg Kurz > hw/9pfs/coth.h | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) >=20 > diff --git a/hw/9pfs/coth.h b/hw/9pfs/coth.h > index c51289903d..f83c7dda7b 100644 > --- a/hw/9pfs/coth.h > +++ b/hw/9pfs/coth.h > @@ -51,7 +51,9 @@ > */ = \ > qemu_coroutine_yield(); = \ > qemu_bh_delete(co_bh); = \ > - code_block; = \ > + do { = \ > + code_block; = \ > + } while (0); = \ > /* re-enter back to qemu thread */ = \ > qemu_coroutine_yield(); = \ > } while (0)