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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=Zv3ZoNV6; 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)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2EEE8606A324; Tue, 3 Nov 2026 08:26:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Zv3ZoNV6 Received: by smtp.kernel.org (Postfix) with ESMTPSA id DAC521F00919; Tue, 3 Nov 2026 08:26:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793694415; bh=W7kXggEh5yfe6fFE4jTh1v6G6P3GKOrRyW+l+lOyS6o=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Zv3ZoNV6A09/e9kgq/U85LcDr1trIfitCwIcOsR3rnB2t5G1R+2TRWnqw+pR3/d9G ZmieS1S8Eob9FcHxlWOVUXdsItDJbIMZ4GSZ3srI7u1hMYB0m/Sx3cNkPTjsfPr2/X mVB5V0QdTR6BryF8n1lYbs7Kg1Au+suC47xkkyxiKQO8FmWMp4ETFUnwCKFUSe8b55 Xvym3MP2LWqa9eqh4wCz0dg6wH1ZWXzh/dXsnqPxL0oXTuVkMgPeZVq4BprfQIcjeK mqSce21Td5+ApzlLra/UdQEd8wvPtFkinREmlUI9iKPEmQTBb5Zgm7RCelWzz9p5gw yM33zUDxL8zNA== Message-ID: <46cb1b29-3e4a-4b2e-88bf-5d7962158823@kernel.org> Date: Tue, 3 Nov 2026 09:26:47 +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 v2] mm/migrate: fix softlockup in do_pages_stat() with huge page arrays To: Qi Xi , Andrew Morton Cc: linux-mm@kvack.org, Zi Yan , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Qiliang Yuan , linux-kernel@vger.kernel.org, wangkefeng.wang@huawei.com, sunnanyong@huawei.com, xiqi2@huawei.com, stable@vger.kernel.org References: <20261103080557.1632382-1-xiqi5703@163.com> 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 11/3/26 09:05, Qi Xi wrote: > From: Qi Xi > > do_pages_stat() walks the user page array in 16-page chunks but never > reschedules, so a huge nr_pages can hold a CPU past the watchdog > threshold on non-preemptible kernels. Add cond_resched() to the loop so > long move_pages() node-query calls yield periodically. > > With KASAN and function tracing enabled, a move_pages() node query > (nodes == NULL) over 10 million page entries (~40GB of mapped memory) > reproduces the softlockup on a 6.6-based arm64 kernel with > CONFIG_PREEMPT_NONE=y. > > In current mainline, only alpha, hexagon and classic m68k can still > select PREEMPT_NONE; stable kernels older than v7.0 still allow it, so > the fix mainly targets pre-v7.0 stable users. > > Fixes: 80bba1290ab5 ("mm: no get_user/put_user while holding mmap_sem in do_pages_stat?") > Cc: > Signed-off-by: Qi Xi > --- > v1 -> v2: describe the repro environment; add Cc stable; no code change. > > mm/migrate.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 7bdcdb57652f..6c2371020cc5 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2545,6 +2545,7 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages, > > chunk_offset += chunk_nr; > nr_pages -= chunk_nr; > + cond_resched(); > } > return nr_pages ? -EFAULT : 0; > } I'll wait a couple more days and will then queue it for the next merge window, not as a hotfix. -- Cheers, David