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 A35BE30EF80 for ; Wed, 1 Jul 2026 14:14:09 +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=1782915251; cv=none; b=KkfYfY8NASPRskHo9wHS7Hk6lw02EjQw0XZ85IpxD3d1u9LEqAX5F8WFfGtjseJIHIlT+5CappmIh2ZekVHOzyDcmGvT9fapd9jrO3mSCWN4Zm7mfbveQreuSZbTOswPGxii+7T8w0jVQTAnz8dSNqskBWGo+M18VVHcru5ARKU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782915251; c=relaxed/simple; bh=nhP18vqq4wQsEMqQYppF+86855YszlrJtiBqGjyPjjo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TlSozF+dnIvEorfjULbgSVZtDJr7A5Ge1i3sfBSLfHBEMCB0v/MDxSBofYwxTpx6cEMm4o3OlXbmiKLETphQ9czurlqhxJKgoqVhbwaYrlLe7iLCnW81aOk60IAzZp5cF+Ksz26q29Yb7g2IuDOxJCk2iH38yeq9eWFVyANditk= 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=TfVejeJe; 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="TfVejeJe" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1782915248; 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: in-reply-to:in-reply-to:references:references; bh=jK1bIKhv9EVwA3j4S4R8XnWiw4Jn8F9JnvPyWp/CSxo=; b=TfVejeJenzw/D2rrRD8qbAdPHrc5+OYQuXESS7zHP/7mi2xOaLGEQjNhicUpZtkbHOu12q 4ZyaBctl/fIJv4rm4qTrlFOsY+JDfz235X82xqOg8FzhzgUJPGBXd64KjAP1NlMyBiR5+H FJG6lz3Lk6bIUOG+4aVlPch2cUI9vFM= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-3-l-qPwwZkNpG4dD-fwBsOQQ-1; Wed, 01 Jul 2026 10:14:06 -0400 X-MC-Unique: l-qPwwZkNpG4dD-fwBsOQQ-1 X-Mimecast-MFC-AGG-ID: l-qPwwZkNpG4dD-fwBsOQQ_1782915244 Received: from mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.95]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 82B3A1944B12; Wed, 1 Jul 2026 14:14:03 +0000 (UTC) Received: from pauld.westford.csb (headnet03.pony-001.prod.iad2.dc.redhat.com [10.2.32.114]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AC9423691C; Wed, 1 Jul 2026 14:14:00 +0000 (UTC) Date: Wed, 1 Jul 2026 10:13:57 -0400 From: Phil Auld To: Waiman Long Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Frederic Weisbecker , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3.1] sched/isolation: Defer freeing of cpumask memblock memory to initcall Message-ID: <20260701141357.GA156809@pauld.westford.csb> References: <20260604182440.430811-1-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260604182440.430811-1-longman@redhat.com> X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 Hi Waiman, On Thu, Jun 04, 2026 at 02:24:40PM -0400 Waiman Long wrote: > When testing a linux-next 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. > > Cannot free reserved memory because of deferred initialization of the memory map > WARNING: mm/memblock.c:904 at __free_reserved_area+0xde/0xf0, CPU#0: swapper/0/0 > : > Call Trace: > > memblock_phys_free+0xcb/0x100 > housekeeping_init+0x14c/0x170 > start_kernel+0x207/0x450 > x86_64_start_reservations+0x24/0x30 > x86_64_start_kernel+0xda/0xe0 > common_startup_64+0x13e/0x141 > > > IOW, we shouldn't free memblock allocated memory so early > in the boot process when memory map isn't fully initialized in > deferred_init_memmap(). > > Fix it by saving the housekeeping cpumask memblock memory to > be freed into a free list in housekeeping_init() and add a new > housekeeping_late_init() helper to defer the actual freeing of memblock > memory to when initcall's are being processed. The non-atomic version > of the llist APIs are used as there is no contention. > > This commit also depends on the presence of commit 7c2eee9c1367 > ("memblock: don't touch memblock arrays when memblock_free() is called > late") to prevent a KASAN UAF bug report [1]. > > [1] https://lore.kernel.org/lkml/20260505051821.1107133-1-longman@redhat.com/ > > Fixes: 27c3a5967f05 ("sched/isolation: Convert housekeeping cpumasks to rcu pointers") > Signed-off-by: Waiman Long > --- > kernel/sched/isolation.c | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > [v3.1] Add __initdata to memblock_freelist > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > index ef152d401fe2..156025ef81b7 100644 > --- a/kernel/sched/isolation.c > +++ b/kernel/sched/isolation.c > @@ -8,6 +8,7 @@ > * > */ > #include > +#include > #include > #include "sched.h" > > @@ -27,6 +28,7 @@ struct housekeeping { > }; > > static struct housekeeping housekeeping; > +static __initdata LLIST_HEAD(memblock_freelist); > > bool housekeeping_enabled(enum hk_type type) > { > @@ -189,10 +191,22 @@ 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()); > + __llist_add((struct llist_node *)omask, &memblock_freelist); This cast is somewhat concerning. I think I see why it's needed. Wrapping it in a proper struct would require more allocating and freeing and make the problem worse. It should work though. Reviewed-by: Phil Auld Cheers, Phil > } > } > > +static int __init housekeeping_late_init(void) > +{ > + struct llist_node *llnode, *pos, *t; > + > + /* Free allocated memblock memory, if any */ > + llnode = __llist_del_all(&memblock_freelist); > + llist_for_each_safe(pos, t, llnode) > + memblock_free(pos, cpumask_size()); > + return 0; > +} > +pure_initcall(housekeeping_late_init); > + > static void __init housekeeping_setup_type(enum hk_type type, > cpumask_var_t housekeeping_staging) > { > -- > 2.54.0 > > --