From nobody Sun Feb 8 05:42:08 2026 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 0A8B82DFF19 for ; Wed, 21 Jan 2026 19:11:07 +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=1769022670; cv=none; b=gYJohXP0kNoXIebb7U61f0B4Pqgcey94Ti/Dwb3o57+0CSKI2DYefwvE1eYoOe/86TO1KdFa6vjwIgLSrYnL3cqXjHZNxuG4MX0xd2hmi4uxY2PSIrIKvuVzikjqD2SrDRjaOHlGcd1CEUwHyDsXxDgZYhgPbD2UD334N9esvpQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769022670; c=relaxed/simple; bh=bErYaAb3B0D38V+6M4gvP8nCNaF/6QJaZ4x/EenMZ0A=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=IJ9o39vNAef7VcFvYlcgI2pbivu7ZTUBCzPIZ5xV4N8PqqXHahrrY9gCYT13i9Zxu3fR3VXsVAZ3fx3JCWVNr3v1NJi6DM2Uny+J+tob05gtNX5EAMgyX2g5Az2QodwtkKda81gNsJsT14d0rDeLDgHjBh1xK2xwum/VlgzlrsI= 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=JYp4XiuJ; 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="JYp4XiuJ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1769022667; 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=SdZRkQhKinw2Zzq19HysXvpWY3I1Lr5Ul0XP6wR89Go=; b=JYp4XiuJEmFTJwullkuqz72UfXK8RRosxvYGjFBoER1VKdjSo8nWNzEN9cHPI+yvzqvfEI uIIIzK0u8NZ4rPF5FV8b4d0pYzkogaqeTTIysDrr1OyY03j9yJl9zvQVw7+P90ADaGb73k LS8721BxfMsAe5RUgtAZzokOU99Q7UI= 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-277-XN4vaPV7PW6RxpaJHQxHwg-1; Wed, 21 Jan 2026 14:11:03 -0500 X-MC-Unique: XN4vaPV7PW6RxpaJHQxHwg-1 X-Mimecast-MFC-AGG-ID: XN4vaPV7PW6RxpaJHQxHwg_1769022662 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (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 956081956096; Wed, 21 Jan 2026 19:11:01 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.89.197]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 3C42919560A2; Wed, 21 Jan 2026 19:10:59 +0000 (UTC) From: Waiman Long To: Mike Rapoport , Andrew Morton , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Wei Yang , David Hildenbrand , Waiman Long Subject: [PATCH] mm/mm_init: Don't call cond_resched() in deferred_init_memmap_chunk() if rcu_preempt_depth() set Date: Wed, 21 Jan 2026 14:10:36 -0500 Message-ID: <20260121191036.461389-1-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: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Content-Type: text/plain; charset="utf-8" Commit 3acb913c9d5b ("mm/mm_init: use deferred_init_memmap_chunk() in deferred_grow_zone()") made deferred_grow_zone() call deferred_init_memmap_chunk() within a pgdat_resize_lock() critical section with irqs disabled. It did check for irqs_disabled() in deferred_init_memmap_chunk() to avoid calling cond_resched(). For a PREEMPT_RT kernel build, however, spin_lock_irqsave() does not disable interrupt but rcu_read_lock() is called. This leads to the following bug report. BUG: sleeping function called from invalid context at mm/mm_init.c:2091 in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0 preempt_count: 0, expected: 0 RCU nest depth: 1, expected: 0 3 locks held by swapper/0/1: #0: ffff80008471b7a0 (sched_domains_mutex){+.+.}-{4:4}, at: sched_domain= s_mutex_lock+0x28/0x40 #1: ffff003bdfffef48 (&pgdat->node_size_lock){+.+.}-{3:3}, at: deferred_= grow_zone+0x140/0x278 #2: ffff800084acf600 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1b4= /0x408 CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W 6.19.0= -rc6-test #1 PREEMPT_{RT,(full) } Tainted: [W]=3DWARN Call trace: show_stack+0x20/0x38 (C) dump_stack_lvl+0xdc/0xf8 dump_stack+0x1c/0x28 __might_resched+0x384/0x530 deferred_init_memmap_chunk+0x560/0x688 deferred_grow_zone+0x190/0x278 _deferred_grow_zone+0x18/0x30 get_page_from_freelist+0x780/0xf78 __alloc_frozen_pages_noprof+0x1dc/0x348 alloc_slab_page+0x30/0x110 allocate_slab+0x98/0x2a0 new_slab+0x4c/0x80 ___slab_alloc+0x5a4/0x770 __slab_alloc.constprop.0+0x88/0x1e0 __kmalloc_node_noprof+0x2c0/0x598 __sdt_alloc+0x3b8/0x728 build_sched_domains+0xe0/0x1260 sched_init_domains+0x14c/0x1c8 sched_init_smp+0x9c/0x1d0 kernel_init_freeable+0x218/0x358 kernel_init+0x28/0x208 ret_from_fork+0x10/0x20 Fix it by checking rcu_preempt_depth() as well to prevent calling cond_resched(). Note that CONFIG_PREEMPT_RCU should always be enabled in a PREEMPT_RT kernel. Fixes: 3acb913c9d5b ("mm/mm_init: use deferred_init_memmap_chunk() in defer= red_grow_zone()") Signed-off-by: Waiman Long --- mm/mm_init.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index fc2a6f1e518f..4d6b6dac6f58 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -2085,7 +2085,12 @@ deferred_init_memmap_chunk(unsigned long start_pfn, = unsigned long end_pfn, =20 spfn =3D chunk_end; =20 - if (irqs_disabled()) + /* + * pgdat_resize_lock() only disables irqs in non-RT + * kernels but calls rcu_read_lock() in a PREEMPT_RT + * kernel. + */ + if (irqs_disabled() || rcu_preempt_depth()) touch_nmi_watchdog(); else cond_resched(); --=20 2.52.0