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Tue, 30 Jun 2026 17:36:48 -0400 X-MC-Unique: AKnM0ZCVOpOVsYN4WalWtA-1 X-Mimecast-MFC-AGG-ID: AKnM0ZCVOpOVsYN4WalWtA_1782855406 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (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 B58E31801303; Tue, 30 Jun 2026 21:36:45 +0000 (UTC) Received: from [10.2.17.12] (unknown [10.2.17.12]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B23F21955D88; Tue, 30 Jun 2026 21:36:41 +0000 (UTC) Message-ID: <661f9976-7c04-45c0-8939-8d5668520863@redhat.com> Date: Tue, 30 Jun 2026 17:36:40 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3.1] sched/isolation: Defer freeing of cpumask memblock memory to initcall To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Frederic Weisbecker Cc: linux-kernel@vger.kernel.org References: <20260604182440.430811-1-longman@redhat.com> Content-Language: en-US From: Waiman Long In-Reply-To: <20260604182440.430811-1-longman@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 On 6/4/26 2:24 PM, 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); > } > } > > +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) > { Ping! Does anyone have comment for this patch? Thanks, Longman