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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FGdo3SDi; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 919A2606A326; Sat, 7 Nov 2026 19:11:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FGdo3SDi Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8494D1F0089F; Sat, 7 Nov 2026 19:11:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794078691; bh=bH4sG8PxPI3XSzLdlTVmZF250KgsDqk6SB0vAlniKYA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FGdo3SDiFOSVJa7QtUjtACayp7b8sVPqRbO3gF7fYZjX1hK6a06frhyCqWXIocQmC ds6G3zS67yyL7FQFLkmzTYK4ZKIp+G06fQLc9+OUIarNaiiHJmP6HZvy9jnnNUsZt8 JY4E9RciuGTOvMYJSNI17z1awb5d+A4ywGBTekNU5dMtJSJkXqWG4MrDSUPWIq29qp 71Sv4e35V4075qjeGekKguMC3mnd+ji4ap3LrRzuzPb9ACN1f6jtotMrxh+WgiteWC FqsFYn/XbrVP1dS+kN4DQWgAQGL3S1OtnmNZTljmNcp9pRKbqLgx7MR4/qn96dlIDI jdCpUvUvq4EjQ== Message-ID: Date: Sat, 7 Nov 2026 20:11:22 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate: fix softlockup in do_pages_move() with huge page arrays To: Zi Yan , shao.mingyin@zte.com.cn, akpm@linux-foundation.org Cc: linux-mm@kvack.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261107213856462Jx8pIdgdtLvPLfOFTwV4X@zte.com.cn> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/7/26 19:45, Zi Yan wrote: > On Sat Nov 7, 2026 at 8:38 AM EST, wrote: >> From: Shao Mingyin >> >> mm/migrate: fix softlockup in do_pages_move() with huge page arrays >> >> do_pages_move() walks the user page array one page at a time. For each >> entry it performs two get_user() calls, an mmap_read_lock()/unlock() >> around a folio walk, and an optional store_status(); none of them has to >> sleep when the arrays stay resident and the rwsem is uncontended. >> move_pages_and_store_status() returns early while the page list is >> empty, so an array whose entries all resolve to the same node can run >> the whole loop without any scheduling point. nr_pages comes straight >> from move_pages(), so a huge array can hold a CPU past the watchdog >> threshold on a non-preemptible kernel; with KASAN and function tracing >> enabled, ten million entries can exceed it. >> >> Add cond_resched() so that long calls yield periodically. >> do_pages_stat() has the same problem and is being fixed separately. In >> current mainline only alpha, hexagon and classic m68k can still select >> PREEMPT_NONE, and they cannot enable CONFIG_NUMA, so this mainly >> targets pre-v7.0 stable kernels. > > This is probably in the same spirit as the do_pages_stat() patch[1][2]. Right, and I'd like to see an actual reproducer, because we sure have a bunch of cond_resched() already in migration code. -- Cheers, David