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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> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Rspamd-Queue-Id: A37201C0002 X-Stat-Signature: wc7yzdmy9nbe55hayw879usds5x6hi3w X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1769053238-979503 X-HE-Meta: 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 IQe1f6Ce +d5j0Lnyp35qFV/DwC6UIj2gXmUOBWV1SydjpORMeDt0A1/pQZHcclwQdKDGUSv8Eic8yjiu5Gi/v/+g89/4UeVhvGUjwwR8Jpzb/RPp2pVDwEBpT9/yU+1cddj6vCeAzZG6FZ/zKWzdS3O0KU60Ll1VqOElGkncw/zuX08oJlfiWg9aT8/mXa0kjwmqnC0DIlg26le4ZopO9WfEBcBmHrsOUTz3UsAlA68P9/ZD2cRb+zT3SjfsVYuVIbtF9n+kx5XwTFBQ1UiNqvULn4aVsfOOIOBU7yrkMFy1fWlA0kSLmsgUxP8vNFFBPnvaI40dgAjocB7DA0OaNm+tIEMaPPTfa6aLO6ibqc0tOp9HajPlCdul1Q4y4v62cqTMglwFLNAm3TUwMrRq1sZ44vMKrheXWbjt8i7V0yWDH5qtjEQ4PyEAh76CQS7E0Q2qD3ZzTorvRw/7Hyt3DcULMfFTErcddVGqm9ai7/mgxDGw4TKjkJMs= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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