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 920A83D6460 for ; Thu, 22 Jan 2026 03:40:38 +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=1769053241; cv=none; b=aLwTPq+dSglDHciDiS85Tnr5aCJ+W1XeiWy0aJtXeCWZ10YBslDRRargRWDeVUejydHCkZAdGT1YWkh7sbggR0a8sHV7p2Ca+CmyLhJO8U1hJY1tzLMuPzhUmvTdUwIraexAzPdDMk7ibI2Z1+W8MHCP3korY4yvHSogP4fufTY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769053241; c=relaxed/simple; bh=WDa6SDWttooZ1e8zS+XJSFNYa2N7GsK65DQ6z4O4SXo=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=UGBE0MDBDQZK67xy+QbY94SbjLXfrdNrkV2apcEELH5UJNuCjqp1AdHefvYA8UL5uyeoIWQqHSvMeSRkAI0ysWMPdwvu0DWt8jDVWY9wH40DC28bgGrSnAySTGTnPPfwxnuaFaSrmJ3zWCeBbUEcUG8AH+nWPHPdQFw9CtICk3c= 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=PFIbfQQw; 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="PFIbfQQw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1769053236; 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=yrAsyPq9OkRG0Lu53Ruwu5hyyipfdn8Du1lCC3wiBJA=; b=PFIbfQQwQvBmrKjTNgZ2IFUh73ukDqrQHZZVWkihJwEO2TITmpZADXqvQxSkpN1E1CQgu/ W+2ICvC9zT4jwbi39aW8I55y20/ukaVrFRModE3u3dC10iE62/h5XsxVCCOX/tNOvPVjZw ZMvT2ayN0bMrSFcVjUxx2O5WK8068g4= Received: from mx-prod-mc-05.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-317-hty7ApdLNLKHD-skSRWDNg-1; Wed, 21 Jan 2026 22:40:34 -0500 X-MC-Unique: hty7ApdLNLKHD-skSRWDNg-1 X-Mimecast-MFC-AGG-ID: hty7ApdLNLKHD-skSRWDNg_1769053232 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 501BF195608A; Thu, 22 Jan 2026 03:40:32 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.89.197]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id B3CCA1800665; Thu, 22 Jan 2026 03:40:29 +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 v2] mm/mm_init: Don't call cond_resched() in deferred_init_memmap_chunk() if rcu_preempt_depth() set Date: Wed, 21 Jan 2026 22:40:17 -0500 Message-ID: <20260122034017.505589-1-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 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_domains_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]=WARN 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() too before calling cond_resched(). Note that rcu_preempt_depth() is a helper defined in the public rcupdate.h header file and is defined whether or not CONFIG_PREEMPT_RCU is defined. By default, CONFIG_PREEMPT_RCU is enabled in the PREEMPT_RT kernel. Fixes: 3acb913c9d5b ("mm/mm_init: use deferred_init_memmap_chunk() in deferred_grow_zone()") Signed-off-by: Waiman Long [v2]: Add "linux/rcupdate.h" include. --- mm/mm_init.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index fc2a6f1e518f..ba0b476c2d45 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -32,6 +32,7 @@ #include #include #include +#include #include "internal.h" #include "slab.h" #include "shuffle.h" @@ -2085,7 +2086,12 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn, spfn = chunk_end; - if (irqs_disabled()) + /* + * pgdat_resize_lock() only disables irqs in non-RT + * kernels but implies rcu_read_lock() in a PREEMPT_RT + * kernel. + */ + if (irqs_disabled() || rcu_preempt_depth()) touch_nmi_watchdog(); else cond_resched(); -- 2.52.0