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 8C358C27C42 for ; Wed, 16 Aug 2023 21:21:40 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qWNx0-0006yj-Fy; Wed, 16 Aug 2023 17:21:10 -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 1qWNwx-0006yW-O1 for qemu-devel@nongnu.org; Wed, 16 Aug 2023 17:21:07 -0400 Received: from smtp-out2.suse.de ([2001:67c:2178:6::1d]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1qWNws-0001hG-7h for qemu-devel@nongnu.org; Wed, 16 Aug 2023 17:21:06 -0400 Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 1D8D01F86C; Wed, 16 Aug 2023 21:21:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1692220861; h=from:from:reply-to: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=6m3T0CEHSiwA6AoWlyxVwouiuf5+wAI8hbMvWWQtrKs=; b=NhzTIZzI6GTZy/K78PG8uRgal2utvbFq6JZQINTUX88Vfy1f0lQ+YhmQsR1eqQpKSup7ds dJK22Ae1Ougb1VRGHz2sFzAVSCalFU8xHF8GVY5tT1NbjIRO64fwJzdguRwL5+uMmhJCTN M+ynyeyTiCW6Vvfu35mcT7ZG/A+Bl2s= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1692220861; h=from:from:reply-to: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=6m3T0CEHSiwA6AoWlyxVwouiuf5+wAI8hbMvWWQtrKs=; b=5Lo/2oLkN6JODziMoiAsG2IunuPjSt1JLwOdq0xDBDBfqMe736ehQ3U2w9KVkFU0ING0wx tbwvRdw5t9xmJ1BA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id A4524133F2; Wed, 16 Aug 2023 21:21:00 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id fpCtG7w93WSHOgAAMHmgww (envelope-from ); Wed, 16 Aug 2023 21:21:00 +0000 From: Fabiano Rosas To: Peter Xu Cc: qemu-devel@nongnu.org, Juan Quintela , Wei Wang , Leonardo Bras Subject: Re: [PATCH v4 8/8] migration: Add a wrapper to cleanup migration files In-Reply-To: References: <20230816142510.5637-1-farosas@suse.de> <20230816142510.5637-9-farosas@suse.de> <87leealt8h.fsf@suse.de> Date: Wed, 16 Aug 2023 18:20:58 -0300 Message-ID: <87edk24rb9.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=2001:67c:2178:6::1d; envelope-from=farosas@suse.de; helo=smtp-out2.suse.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, 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 Peter Xu writes: > On Wed, Aug 16, 2023 at 03:35:24PM -0400, Peter Xu wrote: >> On Wed, Aug 16, 2023 at 03:47:26PM -0300, Fabiano Rosas wrote: >> > Peter Xu writes: >> > >> > > On Wed, Aug 16, 2023 at 11:25:10AM -0300, Fabiano Rosas wrote: >> > >> @@ -2003,6 +1980,8 @@ static int open_return_path_on_source(MigrationState *ms) >> > >> return -1; >> > >> } >> > >> >> > >> + migration_ioc_register_yank(qemu_file_get_ioc(ms->rp_state.from_dst_file)); >> > > >> > > I think I didn't really get why it wasn't paired before yesterday. My >> > > fault. >> > > >> > > Registering from_dst_file, afaict, will register two identical yank objects >> > > because the ioc is the same. >> > > >> > >> > Why do we have two QEMUFiles for the same fd again? >> >> Because qemufile has a "direction" (either read / write)? >> >> > >> > We're bound to crash at some point by trying to qemu_fclose() the two >> > QEMUFiles at the same time. >> >> Even with each qemufile holding a reference on the ioc object? I thought >> it won't crash, but if it will please point that out; or fix it would be >> even better. You're right, it wouldn't crash. But it's still the same ioc object. If qio_channel_close() is called twice, then we could potentially close the fd twice. Which would either error out or close a reused fd. The window is small though, so probably unlikely to ever happen. >> >> > >> > > Should we make migration_file_release() not handle the unregister of >> > > yank(), but leave that to callers? Then we keep the rule of only register >> > > yank for each ioc once. >> > > >> > >> > We need the unregister to be at migration_file_release() so that it >> > takes benefit of the locking while checking the file for NULL. If it >> > moves out then the caller will have to do locking as well. Which >> > defeats the purpose of the patch. >> > >> > I don't understand why you moved the unregister out of channel_close in >> > commit 39675ffffb ("migration: Move the yank unregister of channel_close >> > out"). You called it a "hack" at the time, but looking at the current >> > situation, it seems like a reasonable thing to do: unregister the yank >> > when the ioc refcount drops to 1. >> > >> > I would go even further and say that qemu_fclose should also avoid >> > calling qio_channel_close if the ioc refcnt is elevated. >> >> I'd rather not; I still think it's a hack, always open to be corrected. It's hard to figure out what you mean by hack at times. Even more when reading a years-old commit message. >> >> I think the problem is yank can register anything so it's separate from >> iochannels. If one would like to have ioc close() automatically >> unregister, then one should also register yank transparently without the >> ioc user even aware of yank's existance. Ok, fair point. >> >> Now the condition is the caller register yank itself, then I think the >> caller should unreg it.. not iochannel itself, silently. I think the issue is that we're linking the yank with the QEMUFile for no reason. The migration_yank_iochannel() performs a qio_channel_shutdown() which is an operation on the fd. The QEMUFile just happens to hold a pointer to the ioc. > > I just noticed this is not really copying the list.. let me add the cc list > back, assuming it was just forgotten. I'm sorry, I hit the wrong key while replying. > One more thing to mention is, now I kind of agree probably we should > register yank over each qemufile, as you raised the concern in the other > thread that otherwise qmp_yank() won't set error for the qemufile, which > seems to be unexpected. I haven't made up my mind yet, but I think I'd rather stop setting that error instead of doing it from other places. A shutdown() is mostly a benign operation intended to end the connection. The fact that we use it in some cases to kick the thread out of a possible hang doesn't seem compelling enough to set -EIO. Of course we currently have no other way to indicate that the file was shutdown, so the -EIO will have to stay and that's a discussion for another day.