From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A70C12EC0A4 for ; Thu, 4 Jun 2026 15:24:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780586693; cv=none; b=tuZNfhQFq0HS06yyaiXS1Lwi6AC7VEPpk2UCIVQDN1IHPnQk46vmCyi+5rBzXbB1CLoLCxk8mo0Zn1ASYUKXfFxCL82sHFLSQaoLsyf6ULbvyA+9vsUrJv15GhWp9/jmndiuToQsI46zSzNmCZzfZ5vZTz7NIlrGcoE+dbpOS84= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780586693; c=relaxed/simple; bh=QC+yAe5pmiqVN6wuskV9sUujGuaDrWEvdCQkeCINn3o=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=pNZi0qMjyI/PGhQ3XD+Z7vlQUapBoTjVcw43z0j6AXCXRkf14VALOMJXBWNeTsyhVgjObsmUmD8PO76NBK4PDrC7oJVxw9/JWlAU3hjP9/Jf+wk+oCm+FHdEdfKnsCyCJH3gyIo+fJqOERH8rlW9D8bewb5NiDN446C2X3xXn+w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ICS6rH14; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ICS6rH14" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9FC801F00893; Thu, 4 Jun 2026 15:24:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780586692; bh=ynGGvSyPHETqhnbOAqHM4TR6RSXS4ImZJbectKHoXBU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=ICS6rH14hqdJNpPCs+EOZW95W4BMt3DsT6Rz+FnW4XvOgkplSeZWIRz0NZiBYnJ96 240Ci3I+HoCCxeaCEedO3zfV505f1Sh2+TLCCsIKPzl5XGCF8i+RopEwnrMQaQy6JB HrNRJHnJ24vs8bB8skGqwck3HDNxBJm0cmM86yLkzvJhS8LP46kKHTZTeWH1B68A9C 5WqwMIeWc6iZHjCy1LnTMEbexbvL1CPhxMTIhJ05weYt3bD6Pq7/2fGuKtT4Tj6TXg ckZm0Dv5QuBIGCR/k5WjWTQR9EzbnnE0vFmTNs6cQPk5cihPTSXFoYMWSE3GDOa8NH XxK44nupFBFXg== Date: Thu, 4 Jun 2026 17:24:49 +0200 From: Frederic Weisbecker 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 , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] sched/isolation: Postpone re-allocation of housekeeping cpumask until initcall Message-ID: References: <20260602143951.266768-1-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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260602143951.266768-1-longman@redhat.com> Le Tue, Jun 02, 2026 at 10:39:51AM -0400, Waiman Long a écrit : > 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 adding a new housekeeping_late_init() > helper to defer the re-allocation of the housekeeping cpumasks to > when initcall's are being processed. Also change rcu_reference() by > rcu_reference_check() to prevent incorrect RCU lockdep splat as RCU > will be active in this later boot stage. > > 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 Thanks for fixing it. Just some points below: > --- > kernel/sched/isolation.c | 20 +++++++++++++++----- > 1 file changed, 15 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c > index ef152d401fe2..a947d75b43f1 100644 > --- a/kernel/sched/isolation.c > +++ b/kernel/sched/isolation.c > @@ -164,8 +164,6 @@ int housekeeping_update(struct cpumask *isol_mask) > > void __init housekeeping_init(void) > { > - enum hk_type type; > - > if (!housekeeping.flags) > return; > > @@ -173,17 +171,27 @@ void __init housekeeping_init(void) > > if (housekeeping.flags & HK_FLAG_KERNEL_NOISE) > sched_tick_offload_init(); > +} > + > +static int __init housekeeping_late_init(void) > +{ > + enum hk_type type; > + > + if (!housekeeping.flags) > + return 0; > + > /* > * Realloc with a proper allocator so that any cpumask update > - * can indifferently free the old version with kfree(). > + * can indifferently free the old version with kfree(). This > + * should be done after the completion of deferred_init_memmap(). > */ > for_each_set_bit(type, &housekeeping.flags, HK_TYPE_MAX) { > struct cpumask *omask, *nmask = kmalloc(cpumask_size(), GFP_KERNEL); > > if (WARN_ON_ONCE(!nmask)) > - return; > + return 0; > > - omask = rcu_dereference(housekeeping.cpumasks[type]); > + omask = rcu_dereference_check(housekeeping.cpumasks[type], 1); > > /* We need at least one CPU to handle housekeeping work */ > WARN_ON_ONCE(cpumask_empty(omask)); > @@ -191,7 +199,9 @@ void __init housekeeping_init(void) > RCU_INIT_POINTER(housekeeping.cpumasks[type], nmask); > memblock_free(omask, cpumask_size()); > } > + return 0; > } > +pure_initcall(housekeeping_late_init); Now that it has become an initcall, what prevents other CPUs from accessing the housekeeping cpumasks concurrently and then dereference the free'ed memory? And even as a pre-smp initcall, nothing prevents interrupts or preempting tasks from accessing them either. >From which point on can memblock_free() be called? I see very early calls such as print_unknown_bootoptions()... Thanks. > > static void __init housekeeping_setup_type(enum hk_type type, > cpumask_var_t housekeeping_staging) > -- > 2.54.0 > -- Frederic Weisbecker SUSE Labs