From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 59CC53921E7; Tue, 14 Jul 2026 11:53:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784030007; cv=none; b=oN2IfrsUL8qArdqMnU0wZlAxZkEzqzWIrcnmhKEH3XH3r2K+KhZiAENmbDyA7Wzmd/cMoWIekKJzhR+Stbc37XjrdkGV/Eo5ZRL/hIrRq2ynxdJFrji39REYHmFHzjH8LOYpcCPlE25cJ1DDlyfJlJWVVhQ3kfJ0pff+7jBGwic= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784030007; c=relaxed/simple; bh=2Nf0pzzNTeJOpKeQGGtmDhdnC8W2GgOPVML5TCxAQKQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=R1jSEjR9hyg7MbKTxUUDw1pQMWzOQ53nj0vQCTpKYAve4wmjN9h8m+8Q408/YyGmQSauITgPdjRcnSt5Kw0GHQ+4yQtoagfNhzdiHn+pctYTmpFuIfIvroPw3iRMDWy7IRcgKnAOintYw819NW5A8f9SqXum/HbqGU3JtuSUdoA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HUG61eQr; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HUG61eQr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4375B1F00A3A; Tue, 14 Jul 2026 11:53:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784030006; bh=2Nf0pzzNTeJOpKeQGGtmDhdnC8W2GgOPVML5TCxAQKQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HUG61eQr+qwcx4Kq4681RkPJCJLDTNpPf4qw0k95lvgmE6lqKcMDXgaVntE9jLqLd MsT/5cMj0tdbasDEma3t28y9h5wLSoG5fMXfGniSmj682PlBXb6WlE9qq4LWXspiFM CxQ1C+vistKAF2WILYIfoxuA7dm9uuPDFKKxYO4yoXmGqnylYtKXZNXyOsE2F13+w+ 5JZSD/J0TPhTgIrsO/ZPxX3oaQbEcwwdTS5iZ2Tn2jNmLJMXzXuL3E8+VxVKNcDXZD gZz/o+sDq8I10tXaIv0mNVqnDmokH8GR0hZA+pMbq/PPLtpQYFoBXgVAh5EVc2mLZy bER0gxU5+g+2w== Message-ID: <67930986-152e-483e-a00d-210fe5769a10@kernel.org> Date: Tue, 14 Jul 2026 20:53:16 +0900 Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/page_alloc: don't spin_trylock() in NMI on UP To: Brendan Jackman , Andrew Morton , Brendan Jackman Cc: Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Zi Yan , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , Shakeel Butt , Alexei Starovoitov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, sashiko-bot@kernel.org, stable@vger.kernel.org References: <20260710-spin-trylock-followup-v1-0-affb5fe5ed00@google.com> <20260710-spin-trylock-followup-v1-1-affb5fe5ed00@google.com> <20260710170311.e22bfd21c658e8357ceddeec@linux-foundation.org> <4c969202-a8ed-41a8-9e9a-281a12f6dde3@kernel.org> Content-Language: en-US From: Harry Yoo In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------ku0sMi9hUnR02QaV2h2WUqQg" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --------------ku0sMi9hUnR02QaV2h2WUqQg Content-Type: multipart/mixed; boundary="------------4kdqt064WgNYuyI40EikPph1"; protected-headers="v1" From: Harry Yoo To: Brendan Jackman , Andrew Morton , Brendan Jackman Cc: Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Zi Yan , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , Shakeel Butt , Alexei Starovoitov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, sashiko-bot@kernel.org, stable@vger.kernel.org Message-ID: <67930986-152e-483e-a00d-210fe5769a10@kernel.org> Subject: Re: [PATCH 1/2] mm/page_alloc: don't spin_trylock() in NMI on UP References: <20260710-spin-trylock-followup-v1-0-affb5fe5ed00@google.com> <20260710-spin-trylock-followup-v1-1-affb5fe5ed00@google.com> <20260710170311.e22bfd21c658e8357ceddeec@linux-foundation.org> <4c969202-a8ed-41a8-9e9a-281a12f6dde3@kernel.org> In-Reply-To: --------------4kdqt064WgNYuyI40EikPph1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 7/14/26 6:52 PM, Brendan Jackman wrote: > On Mon Jul 13, 2026 at 4:15 PM UTC, Harry Yoo wrote: >> On 7/13/26 11:31 PM, Brendan Jackman wrote: >>> On Sat Jul 11, 2026 at 12:03 AM UTC, Andrew Morton wrote: >>>> On Fri, 10 Jul 2026 10:42:20 +0000 Brendan Jackman wrote: >>>>> As noted in can_spin_trylock(), using this is unsafe in this contex= t. >>>>> commit 620b46ed6ae17 ("mm/page_alloc: return NULL early from >>>>> alloc_frozen_pages_nolock() in NMI on UP") fixed this on the alloc = side >>>>> but missed the free side. >> >> Ouch, do we allow alloc_pages() -> free_pages_nolock()? >> Didn't notice. >=20 > We don't explicitly disallow that but I'd say it's "forbidden by > default"... >=20 > But I think that's unrelated? It doesn't mean you can't use > free_pages_nolock() from NMI, right? (Would be weird to alloc from > another context and then free in NMI, but I don't think it's "forbidden= > by default" in the way that using unmatched APIs is). If you can't free pages that are not allocated via alloc_pages_nolock(), and if alloc_pages_nolock() always fails, you can't really use free_pages_nolock(). But yeah BPF seems to do that and also the comment says: /* * Can be called while holding raw_spin_lock or from IRQ and NMI for any * page type (not only those that came from alloc_pages_nolock) */ --=20 Cheers, Harry / Hyeonggon --------------4kdqt064WgNYuyI40EikPph1-- --------------ku0sMi9hUnR02QaV2h2WUqQg Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature.asc" -----BEGIN PGP SIGNATURE----- iHUEARYKAB0WIQQQ1ub6gR5ogjaKRmOGXBN6rc5S1gUCalYjLAAKCRCGXBN6rc5S 1onsAP9oH3K4pQoIax+qSGFDjZf1pwd025OJ8HYNXHVk+I8vEwEAiu05mhpZJWF4 zStwwbYgpqkkPFWKzpHYUtNrcO/tdwU= =BfyU -----END PGP SIGNATURE----- --------------ku0sMi9hUnR02QaV2h2WUqQg--