From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 967993AE18F for ; Tue, 5 May 2026 05:19:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777958386; cv=none; b=gK9LAZoEjSCUBnwU0rKYVRsNAcQnWNBRj6We2VfA2f0bhk3Fgoyhj0io3Nx/6AIp4JAoRps+bm4UthyjTKlhh7ULPvwQ3ZLZV+yuQS2kQINVxtqZs5JmtZ9Q/oC7Kvl5LwzAX3jJDlabZx7lsDGDidsUgPIhJsEe9MnupIyOQJ0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777958386; c=relaxed/simple; bh=ZgebocA9+dXBuytqFRRQps+DGohV/fjeIFODlBVatqw=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Q4yOngZ3bHCbuDCEnMrmKH29NEwaREkqLK5wPrSugEp888FI5syBv1O7qR4Jgi+OyJ4483Zb2RnkGaOF0/sB6mRSYT7MKd73hrgev6bJrGbFpcl88K5k+59TGNEh2RtlV2MrUyHV8oSZwjSs3lb7Zp0N7ZL1ntX9L6rXyMXPLno= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=MMEF5E0K; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MMEF5E0K" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1777958383; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=bCjDn4yjFRw23epM0d7XRuBexSfQTG2jaBKXd/qwIUk=; b=MMEF5E0K9ZlCiH+Ea7PJ52IXVdq+9Hhg8Zb17A4FslYlphia4wx6f19IQapJLvTLj0b0Nc z2iRekwxHEgmn+VjjEmx7tuWRbDx/CIDUxaXre+jotRH7uoU5nUtE31JH+St5kW5KNvMqr mhZ6qAYckagvAo7p8jVIFL3dNrMhPow= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-3-J86dB2_5PDiyZ3Qs8xxVaw-1; Tue, 05 May 2026 01:19:38 -0400 X-MC-Unique: J86dB2_5PDiyZ3Qs8xxVaw-1 X-Mimecast-MFC-AGG-ID: J86dB2_5PDiyZ3Qs8xxVaw_1777958376 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CAC7E18005AC; Tue, 5 May 2026 05:19:35 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.2.16.46]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id C3F2130001A1; Tue, 5 May 2026 05:19:30 +0000 (UTC) From: Waiman Long To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Frederic Weisbecker , Mike Rapoport Cc: linux-kernel@vger.kernel.org, Waiman Long Subject: [PATCH] sched/isolation: Don't free memblock allocated cpumasks Date: Tue, 5 May 2026 01:18:21 -0400 Message-ID: <20260505051821.1107133-1-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 When testing a v7.1 kernel with commit 59bd1d914bb5 ("memblock: warn when freeing reserved memory before memory map is initialized"), the following warning was hit when there was a "nohz_full" kernel boot parameter. [ 0.080911] Cannot free reserved memory because of deferred initialization of the memory map [ 0.080911] WARNING: mm/memblock.c:904 at __free_reserved_area+0xde/0xf0, CPU#0: swapper/0/0 : [ 0.080945] Call Trace: [ 0.080947] [ 0.080949] memblock_phys_free+0xcb/0x100 [ 0.080953] housekeeping_init+0x14c/0x170 [ 0.080957] start_kernel+0x207/0x450 [ 0.080961] x86_64_start_reservations+0x24/0x30 [ 0.080965] x86_64_start_kernel+0xda/0xe0 [ 0.080967] common_startup_64+0x13e/0x141 [ 0.080972] The commit states that freeing of reserved memory before the memory map is fully initialized in deferred_init_memmap() would cause access to uninitialized struct pages and may crash when accessing spurious list pointers. However, if the memblock_free() call is deferred to the start of initcall processing in the bootup process, for instance, the following KASAN warning can appear. [ 8.514775] BUG: KASAN: use-after-free in memblock_isolate_range+0x4ac/0x650 [ 8.514775] Read of size 8 at addr ffff88a07fe6a000 by task swapper/0/1 : [ 8.514775] Call Trace: [ 8.514775] [ 8.514775] kasan_report+0xb2/0x1b0 [ 8.514775] memblock_isolate_range+0x4ac/0x650 [ 8.514775] memblock_phys_free+0xc4/0x190 [ 8.514775] housekeeping_late_init+0x257/0x280 [ 8.514775] do_one_initcall+0xaa/0x470 [ 8.514775] do_initcalls+0x1b4/0x1f0 [ 8.514775] kernel_init_freeable+0x4b5/0x550 [ 8.514775] kernel_init+0x1c/0x150 [ 8.514775] ret_from_fork+0x5dc/0x8e0 [ 8.514775] ret_from_fork_asm+0x1a/0x30 [ 8.514775] It is likely that memblock_discard() may discard memblock data needed for memblock_free(). One workaround for now to avoid these warning/bug messages is to keep the memblock allocated cpumasks even if they are no longer needed until the memblock subsystem is properly updated to handle memblock_free(). On most systems, memory occuipied by a cpumask is pretty small. So not much memory will be wasted if the memblock cpumasks are not freed. Signed-off-by: Waiman Long --- kernel/sched/isolation.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index ef152d401fe2..ad9b1a1104e3 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -189,7 +189,13 @@ void __init housekeeping_init(void) WARN_ON_ONCE(cpumask_empty(omask)); cpumask_copy(nmask, omask); RCU_INIT_POINTER(housekeeping.cpumasks[type], nmask); - memblock_free(omask, cpumask_size()); + + /* + * TODO: Don't free memblock allocated cpumasks until the + * memblock subystem is able to handle the memblock_free() + * properly. + */ + // memblock_free(omask, cpumask_size()); } } -- 2.53.0