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 4CE2AC7619A for ; Mon, 27 Mar 2023 13:19:07 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pgmkI-0005zY-QU; Mon, 27 Mar 2023 09:18:46 -0400 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 1pgmkD-0005z5-69 for qemu-devel@nongnu.org; Mon, 27 Mar 2023 09:18:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pgmkB-0005Lh-Aw for qemu-devel@nongnu.org; Mon, 27 Mar 2023 09:18:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679923118; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+vmB/Nixa/TLYuBmbhbDZvNHLLMoiQzXaLoGDz8G4MU=; b=i1XzjJzvAOKrjOScOou/VPmqk+DuZVdYhgcWXdMwlotVhyaUZPpaQHJzL71HN2Z7KP+1lB WVkvIdcY1LFvbarsHLAQkYev88TvVE7QR2vUUymTX+QlpcLTmhUEIb094cdCPhYwtxNs5i tBG+fcNLgQq/UW9hPVJSMEQdKROTlV8= 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-657-2xdyXa0xNJeqgzbdALS6rw-1; Mon, 27 Mar 2023 09:18:35 -0400 X-MC-Unique: 2xdyXa0xNJeqgzbdALS6rw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 26C6F85530D; Mon, 27 Mar 2023 13:18:35 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.191]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 59162492B0A; Mon, 27 Mar 2023 13:18:34 +0000 (UTC) Date: Mon, 27 Mar 2023 15:18:33 +0200 From: Kevin Wolf To: qemu-block@nongnu.org Cc: hreitz@redhat.com, eesposit@redhat.com, ldoktor@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH for-8.0] block/export: Fix graph locking in blk_get_geometry() call Message-ID: References: <20230327113959.60071-1-kwolf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230327113959.60071-1-kwolf@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.129.124; 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=unavailable 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 27.03.2023 um 13:39 hat Kevin Wolf geschrieben: > blk_get_geometry() eventually calls bdrv_nb_sectors(), which is a > co_wrapper_mixed_bdrv_rdlock. This means that when it is called from > coroutine context, it already assume to have the graph locked. > > However, virtio_blk_sect_range_ok() in block/export/virtio-blk-handler.c > (used by vhost-user-blk and VDUSE exports) runs in a coroutine, but > doesn't take the graph lock - blk_*() functions are generally expected > to do that internally. This causes an assertion failure when accessing > an export for the first time if it runs in an iothread. > > This is an example of the crash: > > $ ./storage-daemon/qemu-storage-daemon --object iothread,id=th0 --blockdev file,filename=/home/kwolf/images/hd.img,node-name=disk --export vhost-user-blk,addr.type=unix,addr.path=/tmp/vhost.sock,node-name=disk,id=exp0,iothread=th0 > qemu-storage-daemon: ../block/graph-lock.c:268: void assert_bdrv_graph_readable(void): Assertion `qemu_in_main_thread() || reader_count()' failed. > > (gdb) bt Oops, git helpfully removed the "comments"... (gdb) bt #0 0x00007ffff6eafe5c in __pthread_kill_implementation () from /lib64/libc.so.6 #1 0x00007ffff6e5fa76 in raise () from /lib64/libc.so.6 #2 0x00007ffff6e497fc in abort () from /lib64/libc.so.6 #3 0x00007ffff6e4971b in __assert_fail_base.cold () from /lib64/libc.so.6 #4 0x00007ffff6e58656 in __assert_fail () from /lib64/libc.so.6 #5 0x00005555556337a3 in assert_bdrv_graph_readable () at ../block/graph-lock.c:268 #6 0x00005555555fd5a2 in bdrv_co_nb_sectors (bs=0x5555564c5ef0) at ../block.c:5847 #7 0x00005555555ee949 in bdrv_nb_sectors (bs=0x5555564c5ef0) at block/block-gen.c:256 #8 0x00005555555fd6b9 in bdrv_get_geometry (bs=0x5555564c5ef0, nb_sectors_ptr=0x7fffef7fedd0) at ../block.c:5884 #9 0x000055555562ad6d in blk_get_geometry (blk=0x5555564cb200, nb_sectors_ptr=0x7fffef7fedd0) at ../block/block-backend.c:1624 #10 0x00005555555ddb74 in virtio_blk_sect_range_ok (blk=0x5555564cb200, block_size=512, sector=0, size=512) at ../block/export/virtio-blk-handler.c:44 #11 0x00005555555dd80d in virtio_blk_process_req (handler=0x5555564cbb98, in_iov=0x7fffe8003830, out_iov=0x7fffe8003860, in_num=1, out_num=0) at ../block/export/virtio-blk-handler.c:189 #12 0x00005555555dd546 in vu_blk_virtio_process_req (opaque=0x7fffe8003800) at ../block/export/vhost-user-blk-server.c:66 #13 0x00005555557bf4a1 in coroutine_trampoline (i0=-402635264, i1=32767) at ../util/coroutine-ucontext.c:177 #14 0x00007ffff6e75c20 in ?? () from /lib64/libc.so.6 #15 0x00007fffefffa870 in ?? () #16 0x0000000000000000 in ?? () I'm adding this back while applying (but with indentation this time so that git doesn't interpret it as comments). Kevin > Fix this by creating a new blk_co_get_geometry() that takes the lock, > and changing blk_get_geometry() to be a co_wrapper_mixed around it. > > To make the resulting code cleaner, virtio-blk-handler.c can directly > call the coroutine version now (though that wouldn't be necessary for > fixing the bug, taking the lock in blk_co_get_geometry() is what fixes > it). > > Fixes: 8ab8140a04cf771d63e9754d6ba6c1e676bfe507 > Reported-by: Lukáš Doktor > Signed-off-by: Kevin Wolf