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 A13D7EDE989 for ; Fri, 15 Sep 2023 01:57:25 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qgy4Q-0001Bo-JN; Thu, 14 Sep 2023 21:56:34 -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 1qgy4O-0001Bd-Qr for qemu-devel@nongnu.org; Thu, 14 Sep 2023 21:56:32 -0400 Received: from smtp-out1.suse.de ([2001:67c:2178:6::1c]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1qgy4N-0007W7-1O for qemu-devel@nongnu.org; Thu, 14 Sep 2023 21:56:32 -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-out1.suse.de (Postfix) with ESMTPS id 6464B218DF; Fri, 15 Sep 2023 01:56:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1694742987; 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=QG8Hd9AANb+Ua9NJ6ImZE7FB1rpMvm23l+0eGlve+Yg=; b=qJ3tmrvbY+wdtnYgQzx/Q2+vcYKGfxEq8prUmeH0Pi4R1ahvZDaw86KAKo1o66aoHWqx+Y yFrGW7TOa99AtOZiNL2FsEPjPLot/MUaWANftYH4SA8xEoqwIXJYvhNDHNOSnclbo8HYoh u5CVpPgRImtAh51avtf+9rzh7CFlIhI= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1694742987; 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=QG8Hd9AANb+Ua9NJ6ImZE7FB1rpMvm23l+0eGlve+Yg=; b=DIOUc9gpa2E5TmoGzzwBSKRVvtk4IVkTRPefhsKFlXzlWxu+y9pIcHQs5Oz2IQXGIzY6bR HALGPuXoYvp1t4BQ== 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 C464C1358A; Fri, 15 Sep 2023 01:56:26 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id cL3DHcq5A2VsEwAAMHmgww (envelope-from ); Fri, 15 Sep 2023 01:56:26 +0000 From: Fabiano Rosas To: Peter Xu Cc: Stefan Hajnoczi , Juan Quintela , Leonardo Bras , qemu-devel@nongnu.org Subject: Re: QEMU migration-test CI intermittent failure In-Reply-To: References: <20230913192301.GA917052@fedora> <87r0n1kggo.fsf@suse.de> <87edj0kcz7.fsf@suse.de> <87bke4kasr.fsf@suse.de> <87led8e9vv.fsf@suse.de> <87r0n0nz6u.fsf@suse.de> Date: Thu, 14 Sep 2023 22:56:23 -0300 Message-ID: <87o7i4nqrc.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=2001:67c:2178:6::1c; envelope-from=farosas@suse.de; helo=smtp-out1.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 Thu, Sep 14, 2023 at 07:54:17PM -0300, Fabiano Rosas wrote: >> Fabiano Rosas writes: >> >> > Peter Xu writes: >> > >> >> On Thu, Sep 14, 2023 at 12:57:08PM -0300, Fabiano Rosas wrote: >> >>> I managed to reproduce it. It's not the return path error. In hindsight >> >>> that's obvious because that error happens in the 'recovery' test and this >> >>> one in the 'plain' one. Sorry about the noise. >> >> >> >> No worry. It's good to finally identify that. >> >> >> >>> >> >>> This one reproduced with just 4 iterations of preempt/plain. I'll >> >>> investigate. >> > >> > It seems that we're getting a tcp disconnect (ECONNRESET) on when doing >> > that shutdown() on postcopy_qemufile_src. The one from commit 6621883f93 >> > ("migration: Fix potential race on postcopy_qemufile_src"). >> > >> > I'm trying to determine why that happens when other times it just >> > returns 0 as expected. >> > >> > Could this mean that we're kicking the dest too soon while it is still >> > receiving valid data? >> >> Looking a bit more into this, what's happening is that >> postcopy_ram_incoming_cleanup() is shutting the postcopy_qemufile_dst >> while ram_load_postcopy() is still running. >> >> The postcopy_ram_listen_thread() function waits for the >> main_thread_load_event, but that only works when not using preempt. With >> the preempt thread, the event is set right away and we proceed to do the >> cleanup without waiting. >> >> So the assumption of commit 6621883f93 that the incoming side knows when >> it has finished migrating is wrong IMO. Without the EOS we're relying on >> the chance that the shutdown() happens after the last recvmsg has >> returned and not during it. >> >> Peter, what do you think? > > That's a good point. > > One thing to verify that (sorry, I still cannot reproduce it myself, which > is so weirdly... it seems loads won't really help reproducing this) is to > let the main thread wait for all requested pages to arrive: > > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c > index 29aea9456d..df055c51ea 100644 > --- a/migration/postcopy-ram.c > +++ b/migration/postcopy-ram.c > @@ -597,6 +597,12 @@ int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis) > trace_postcopy_ram_incoming_cleanup_entry(); > > if (mis->preempt_thread_status == PREEMPT_THREAD_CREATED) { > + /* > + * NOTE! it's possible that the preempt thread is still handling > + * the last pages to arrive which were requested by faults. Making > + * sure nothing is left behind. > + */ > + while (qatomic_read(&mis->page_requested_count)); > /* Notify the fast load thread to quit */ > mis->preempt_thread_status = PREEMPT_THREAD_QUIT; > if (mis->postcopy_qemufile_dst) { > > If that can work solidly, we can figure out a better way than a dead loop > here. Yep, 2000+ iterations so far and no error. Should we add something that makes ram_load_postcopy return once it's finished? Then this code could just set PREEMPT_THREAD_QUIT and join the preempt thread.