From patchwork Mon Oct 7 19:16:34 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Tokarev X-Patchwork-Id: 13825196 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 020B4CFB455 for ; Mon, 7 Oct 2024 19:18:33 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sxtFD-0005an-0d; Mon, 07 Oct 2024 15:18:11 -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 1sxtF9-0005X6-TY; Mon, 07 Oct 2024 15:18:08 -0400 Received: from isrv.corpit.ru ([86.62.121.231]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sxtF7-0004CP-PK; Mon, 07 Oct 2024 15:18:07 -0400 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id 273D29624E; Mon, 7 Oct 2024 22:16:49 +0300 (MSK) Received: from tls.msk.ru (mjt.wg.tls.msk.ru [192.168.177.130]) by tsrv.corpit.ru (Postfix) with SMTP id 018F714F72E; Mon, 7 Oct 2024 22:16:56 +0300 (MSK) Received: (nullmailer pid 2592752 invoked by uid 1000); Mon, 07 Oct 2024 19:16:54 -0000 From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Fabiano Rosas , Peter Xu , Michael Tokarev Subject: [Stable-9.1.1 17/32] migration/multifd: Fix rb->receivedmap cleanup race Date: Mon, 7 Oct 2024 22:16:34 +0300 Message-Id: <20241007191654.2592616-17-mjt@tls.msk.ru> X-Mailer: git-send-email 2.39.5 In-Reply-To: References: MIME-Version: 1.0 Received-SPF: pass client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, 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 From: Fabiano Rosas Fix a segmentation fault in multifd when rb->receivedmap is cleared too early. After commit 5ef7e26bdb ("migration/multifd: solve zero page causing multiple page faults"), multifd started using the rb->receivedmap bitmap, which belongs to ram.c and is initialized and *freed* from the ram SaveVMHandlers. Multifd threads are live until migration_incoming_state_destroy(), which is called after qemu_loadvm_state_cleanup(), leading to a crash when accessing rb->receivedmap. process_incoming_migration_co() ... qemu_loadvm_state() multifd_nocomp_recv() qemu_loadvm_state_cleanup() ramblock_recv_bitmap_set_offset() rb->receivedmap = NULL set_bit_atomic(..., rb->receivedmap) ... migration_incoming_state_destroy() multifd_recv_cleanup() multifd_recv_terminate_threads(NULL) Move the loadvm cleanup into migration_incoming_state_destroy(), after multifd_recv_cleanup() to ensure multifd threads have already exited when rb->receivedmap is cleared. Adjust the postcopy listen thread comment to indicate that we still want to skip the cpu synchronization. CC: qemu-stable@nongnu.org Fixes: 5ef7e26bdb ("migration/multifd: solve zero page causing multiple page faults") Signed-off-by: Fabiano Rosas Link: https://lore.kernel.org/r/20240917185802.15619-3-farosas@suse.de [peterx: added comment in migration_incoming_state_destroy()] Signed-off-by: Peter Xu (cherry picked from commit 4ce56229087860805877075ddb29dd44578365a9) Signed-off-by: Michael Tokarev diff --git a/migration/migration.c b/migration/migration.c index 3dea06d577..ae2be31557 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -378,6 +378,11 @@ void migration_incoming_state_destroy(void) struct MigrationIncomingState *mis = migration_incoming_get_current(); multifd_recv_cleanup(); + /* + * RAM state cleanup needs to happen after multifd cleanup, because + * multifd threads can use some of its states (receivedmap). + */ + qemu_loadvm_state_cleanup(); if (mis->to_src_file) { /* Tell source that we are done */ diff --git a/migration/savevm.c b/migration/savevm.c index 6bb404b9c8..b71eba218f 100644 --- a/migration/savevm.c +++ b/migration/savevm.c @@ -2983,7 +2983,10 @@ int qemu_loadvm_state(QEMUFile *f) trace_qemu_loadvm_state_post_main(ret); if (mis->have_listen_thread) { - /* Listen thread still going, can't clean up yet */ + /* + * Postcopy listen thread still going, don't synchronize the + * cpus yet. + */ return ret; } @@ -3026,7 +3029,6 @@ int qemu_loadvm_state(QEMUFile *f) } } - qemu_loadvm_state_cleanup(); cpu_synchronize_all_post_init(); return ret;