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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 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; 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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--