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McKenney" Subject: Re: [PATCH v3] mm/mm_init: Don't cond_resched() in deferred_init_memmap_chunk() if called from deferred_grow_zone() Message-Id: <20260122112920.2b435873a0cc5f396df5d1a7@linux-foundation.org> In-Reply-To: <20260122184343.546627-1-longman@redhat.com> References: <20260122184343.546627-1-longman@redhat.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 453F640011 X-Stat-Signature: xxec57z7uqpxrupfsothfyemk41caniq X-Rspam-User: X-HE-Tag: 1769110163-458103 X-HE-Meta: U2FsdGVkX1+vdiMYoVmyHkjTuPNM4YhcQHqsbHyYFu6CCkY1TEo6nBhTw4oJM1Gff+6iH7tYUqLFUz6gKmrRgq4qivte8KATpqHqYsXmp9nKbBce9WRJy0dVTcxb6r4QnXq5HjRWxbUgTSVqgnmpZC0dq8+y/qEWsolWBNi1quY+xCCeJMnvTc3kQBrhlYMaajaZL3+A4aEDShOzcqVVEviysElz1gsGjWTBK0659hPpnnVGabGHR6TutkHXscg04L7dRwp62TyFoTMU/KezBf2+wRBzDrsyH9rgX2wLnYkqUSnhg08vm/m8w9dxzfE791GoOmQhDjJWtbNUius9W4BPDVaWxi6hn3cEXYLskY2X269gBlsFL4L4zKTlm+88tZ3aSM05MkAWfg6986BSphdtcLfDFG8VNRdCw+Za/jHR0LgqQ1Vt7XqrMle6hbVXwO7/IqHBOQuNZU0TgM5Dd2vFDxpFy60FrEFe6jTJ8HssdiZ8+DI3WJfcPCppR4Ed/7HnlHCRPUDBLkZh6fA0oxhFeWhsoOpNNNxAsgZZt+AxdlNf+qsRQAE0pjityqqdkC+kSPLnDAlExwRP45l6sq+4vZkectMPQMGxz6ELFzAuzsCIQ1FXZgv+cDbvl6z1zpq5vgo1+GHzgxJvIUGk2uxTPEpvqo29p55XxiOEgPkyXEoRzruN7C6WOWve0GpDlORpAc4EK0Bs8MzEZcD0qRS5EW84r4j6ju/yjzWVMPHN5t0QGcEdGBPpyMJuuxjuDd6857m3ycK2D854jNP955KU2rYUDaWSiS/GXKnIarwSeUBwBCKx2v/YZ5opAEKngsRC9xO+ClR4Q6iQ4/zL2w6FwmkFm4+z6ySriAJ6eq5amBKpPifbBOJ7xqL3k2Nfk1KWtTNusHsDzwV4r3S9ct/XPslBo+za0jt1GKSykR1cGqBUzTta6JeyqZVVS0amw1T9Pc6WnKqhc0z0DGc x4N3pXWQ 5tU54Q//2elDKRZX7QEcqrOj+us1MlNbLO874mva4z3HAiZDcL1HiUPpw0Ns4okjAY0Bt0DtB1PI33t1TbkD8AA9+jmbfXTi8gtRG0BQ7PWYl2/NZ+yz4nWRGv5SyBMN49zInNElrIUvDVG7sJrga9sK8E4DL7NRgcZX5HODKGtF6Saq6wyIrnb54JaMhWeeK5ZPp83/7XfUnBsb+z8WJj2qx2GDHLJ5J0L9j1HudVrD2ijvBfjf+pGVLkwtBTE+RUgtDRnwLAe3XlT1WP28AYMGF5U9Urofad/yX9K8R+5rZEmF22g+Y2bJA+u5b6YjEFuPufQbnEgzbSUSPxaQsQ4gx8CBaK+wzQEt984am/pdlmRk5nxcE6g80jlyoX+tL3UxuwHNeCKTiatw= 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: On Thu, 22 Jan 2026 13:43:43 -0500 Waiman Long wrote: > 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 > > @@ -2085,10 +2085,10 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn, > > spfn = chunk_end; > > - if (irqs_disabled()) > - touch_nmi_watchdog(); > - else > + if (can_resched) > cond_resched(); > + else > + touch_nmi_watchdog(); > } > } Disables the cond_resched() in some situations. Can this reintroduce the watchdog warnings which that cond_resched() was intended to prevent? The cond_resched() was added by da97f2d56bbd ("mm: call cond_resched() from deferred_init_memmap()"). Pasha's 2020 patch replaced touch_nmi_watchdog() with cond_resched() to prevent RCU stall warnings. So I think the answer to my question is yes, going back to touch_nmi_watchdog() could reintroduce those RCU warnings.