From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 77F78CF6C1D for ; Wed, 7 Jan 2026 09:29:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E11D76B0099; Wed, 7 Jan 2026 04:29:25 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id DF3A96B00A2; Wed, 7 Jan 2026 04:29:25 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D13286B00AB; Wed, 7 Jan 2026 04:29:25 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id C1A726B0099 for ; Wed, 7 Jan 2026 04:29:25 -0500 (EST) Received: from smtpin07.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay04.hostedemail.com (Postfix) with ESMTP id 97C1E1A0223 for ; Wed, 7 Jan 2026 09:29:25 +0000 (UTC) X-FDA: 84304644690.07.7A6BD31 Received: from mail-ej1-f54.google.com (mail-ej1-f54.google.com [209.85.218.54]) by imf23.hostedemail.com (Postfix) with ESMTP id A154C140002 for ; Wed, 7 Jan 2026 09:29:23 +0000 (UTC) Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b="gX/YIXjL"; spf=pass (imf23.hostedemail.com: domain of mattbobrowski@google.com designates 209.85.218.54 as permitted sender) smtp.mailfrom=mattbobrowski@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1767778163; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=qAmBFvHljQCF3L3oXr+WZULma4DAz/lJTXBequgmr24=; b=YB+vKefymQgbjV6ZZuzG2Zbdj3TU0VnvY/yMHjOmOEp8xd2yoZZqo57/J92gwKcoHef6YX 4dobh/ecqYRgWJFLoEyOxDFboGQdPywCij3aPVFT4s+oEd51pUEMXlyaasJ4I/h/PB+7SD BVAc/919/zbRxOP8WHuZYepSY1UpgMg= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=google.com header.s=20230601 header.b="gX/YIXjL"; spf=pass (imf23.hostedemail.com: domain of mattbobrowski@google.com designates 209.85.218.54 as permitted sender) smtp.mailfrom=mattbobrowski@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1767778163; a=rsa-sha256; cv=none; b=AGnDPK5x4QU16512HqEsN0v6KmcBALFNNOeJJfK+ECDV9TXiuJhaTEYnaD0D1Di9i9s1rm c54shodZMOx2P473/NejhXbFj6Ls3qCaKFhMs624ofLiqq1FMB1+VXgqpHriuJP6o8fcIH lK3lw5pBvY97LWwlokzcvm/Thh5rM9U= Received: by mail-ej1-f54.google.com with SMTP id a640c23a62f3a-b725ead5800so257762166b.1 for ; Wed, 07 Jan 2026 01:29:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1767778162; x=1768382962; darn=kvack.org; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=qAmBFvHljQCF3L3oXr+WZULma4DAz/lJTXBequgmr24=; b=gX/YIXjLA5vnDSF8hF/EucYt1VcevubGTMV7PVTE3+pa7XuxKCqmS71FWUdF8YZmZW Tc+XUfjNHK0pEETb2lDoc7BoF3zwap5tXZFVdBaZd4zuOnlCXEE5QCsNl65fDQ1OYWqb eQzMQCJStqrAtbkTwbLCOKZMdYBmBhYQI+ZmkceJmUDwBsasBcYWPS6t0PwkNJvHesnq lGcFP9u5psKK/cAq7i2xB+NTXrLaP5E84lQz9yB1yNsWCNrwfcLwm+1YD3EvB8BwdbCY S7rHFLMkpc3ME7c5EFIkZb9ccg0piGpTIWt9pPVPG2gFyIjGnCtbssw7JtHsynHtQPDe PQ1w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1767778162; x=1768382962; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=qAmBFvHljQCF3L3oXr+WZULma4DAz/lJTXBequgmr24=; b=pieWrmKecZWXJfMZCMirITrYxX9WVU8YzFX3RYJQ6zqUTEY2dpHbAvW6OWUAHquAzk cINE1f7HQVIg5MbLPIODz4q/W1gy1oGwUZtfwsxweoAraLXk4hEWsG2kY/1cDgGB4KZO 5iBhlsJujcmvHp6x4oNF8aBSQJuAn+rBTDtEzLnap4yHRrbXWK0e/Qm5ZD3paHTEY5Jy YgUC7+bD0d91oBB7VPqbBer2P9eJLZW4v/t0bzegOfwlBlu5oaQGGvFnRQ8XVXTUp9vO i9Dd53Jwxsry7ZeElngXvDTgkrOEa1WnQg1ic+lZkPwUEu/LeJ8OHJvK8LliRgN3RAqY b1tg== X-Forwarded-Encrypted: i=1; AJvYcCWWFSs245XudTXZRdYHrJdoQhEc8yXx5bhpGC5SKEEIGIGF0i8b79EJnyajm3rEQgNA0ZpTPD0P0A==@kvack.org X-Gm-Message-State: AOJu0YzMC+oz6c4uVk/Qw5S7zMPalvUy3YUCYc9B+gVB1EJIKKoEAP4y 8M4SDj90pBLUI+R6T+pRig8GigsQxPajdy7iAW+1LbdZ9LE1qifUhQt6K7g3KCqxzA== X-Gm-Gg: AY/fxX41FwN6H/oOvvlaERvmVwJTQFRY8732YwTBia+gt+yjbcLQq3iggU1zgK1IFUv bv0fViponyClrYuSm3DWGMoYocm7JKJn0Z5mENiMeIN4FGDwc4MCc/18u3SvEbQFo8rWqjaqow7 62MTXP/f07j02T0gPRFTOt6PVkNuTq2lTl0IrG7UnhdJjrUggSAVKlcjce32JGYsix+3cL7QZKv MECe8/SU8ev7DFK5sHKHYwNZ0r108718hkXkx2idtHFU/5BsWT0lUL+tcZa7WOiwCIjNxXYXl+e Y5M8E2c2IJMZZEaDR18TwfZWTwg7D+y4QaXP4Cvj2c9wzyCw6XAKxTVkNStYL+JMvSalBURmyAS UC7DPervojzuFpYWeK2NaFnAtEfwhAQ6ch3GdlpDYMaJ8yQgLzIwBRdVXeXd2MTESBYl4RZm4LU 2M8dgFaYqBQaAMESwOAloRlKfYCO7cY73maroTyxPd7f83fMmuO69Gug== X-Google-Smtp-Source: AGHT+IEZ569HZDlJCwAETH6UvXRvz+tkMRRxeKTBnNpUb4XcosV6KbxuzsGMXy5rQgg3tcmEAr8VOQ== X-Received: by 2002:a17:907:cd0e:b0:b73:5b9a:47c7 with SMTP id a640c23a62f3a-b8445413775mr187603266b.51.1767778161682; Wed, 07 Jan 2026 01:29:21 -0800 (PST) Received: from google.com (14.59.147.34.bc.googleusercontent.com. [34.147.59.14]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b842a4cfd97sm444211066b.36.2026.01.07.01.29.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Jan 2026 01:29:21 -0800 (PST) Date: Wed, 7 Jan 2026 09:29:16 +0000 From: Matt Bobrowski To: Kumar Kartikeya Dwivedi , g@google.com Cc: Alexei Starovoitov , Tejun Heo , Roman Gushchin , bpf , linux-mm , LKML , JP Kobryn , Alexei Starovoitov , Daniel Borkmann , Shakeel Butt , Michal Hocko , Johannes Weiner Subject: Re: [PATCH bpf-next v4 3/6] mm: introduce bpf_get_root_mem_cgroup() BPF kfunc Message-ID: References: <20251223044156.208250-1-roman.gushchin@linux.dev> <20251223044156.208250-4-roman.gushchin@linux.dev> <7ia4ms2zwuqb.fsf@castle.c.googlers.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A154C140002 X-Stat-Signature: rw9gj1c3ui9bpi8exdgemg6eif86jqfh X-Rspam-User: X-HE-Tag: 1767778163-428800 X-HE-Meta: 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 qFKbukZi +Dw51grPgiTbwh9wtZ592QLNFZnznhZCDZfyttizA545v21GKAwu5JWzJWEa/5Bv65ptGq9qTKOJCM3adOy31PA2tZ1otTukzA8JSNSx9+eIbQ8L+IyYkJjrDVXrisPyZXqsTKos0HXveTUwTXzTyOkGkj0OCYGVkfq8LIA8/6aqSi8TNN0qaqhx7g5S6Nz/bmlU4jGGQbv636eOLmg3QS7G7YVxiIQcjqHOj0WZ15cQpvgHYJuoSXmtt6D9L9P6SnC9YX2c9k6C8yqLZjcmHpR0zadW/Et3Bu/6kUqrAWz+CZTNLbAzrf8+5CGiGFiT6yohIouBq+ChTxwTJhXVpp51VgpHHLHBzKOoImAerlnvjKq8LHcayxSinWProJlMvwPqZgfBwBErOTJVg+sovw6FHtrCHrXp9j7WTYtoyW0RoONo2p9/CBBiuMbK+81CbUq9yjFYp8Ktv+2mfoPup/9tl5A/8yFJokOyAD/OoDbBUgnM= 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 Tue, Jan 06, 2026 at 04:13:24PM +0100, Kumar Kartikeya Dwivedi wrote: > On Mon, 5 Jan 2026 at 22:04, Matt Bobrowski wrote: > > > > On Mon, Jan 05, 2026 at 08:05:54AM -0800, Alexei Starovoitov wrote: > > > On Sun, Jan 4, 2026 at 11:49 PM Matt Bobrowski wrote: > > > > > > > > > > > > > > No need for a new KF flag. Any struct returned by kfunc should be > > > > > trusted or trusted_or_null if KF_RET_NULL was specified. > > > > > I don't remember off the top of my head, but this behavior > > > > > is already implemented or we discussed making it this way. > > > > > > > > Hm, I do not see any evidence of this kind of semantic currently > > > > implemented, so perhaps it was only discussed at some point. Would you > > > > like me to put forward a patch that introduces this kind of implicit > > > > trust semantic for BPF kfuncs returning pointer to struct types? > > > > > > Hmm. What about these: > > > BTF_ID_FLAGS(func, scx_bpf_cpu_rq) > > > BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_RET_NULL) > > > BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_RET_NULL | KF_RCU_PROTECTED) > > > > > > I thought they're returning a trusted pointer without acquiring it. > > > iirc the last one returns trusted in RCU CS, > > > but the first two return just a legacy ptr_to_btf_id ? > > > This is something to fix asap then. > > > > No, AFAIU they do not. These simply return a regular pointer to BTF ID > > (PTR_TO_BTF_ID), rather than a formally "trusted" pointer (which would > > carry the PTR_TRUSTED flag or a ref_obj_id). scx_bpf_cpu_curr returns > > a MEM_RCU pointer (via KF_RCU_PROTECTED), which is somewhat considered > > to be trusted within a RCU read-side critical section *ONLY*. > > > > Kumar/Tejun, > > Yeah, they don't return a trusted pointer. I think it would make sense > to change the behavior here by default. Thanks for chiming in and confirming this Kumar! I also agree that any BPF kfunc returning a pointer should be treated as being implicitly trusted by default. I can't think of any scenario whereby a BPF kfunc would want to return a pointer that'd fundamentally be untrusted, but there always could be some exceptions. Anyway, I will work on this and send something through for review soon. > A non-trusted pointer cannot be passed to kfuncs taking trusted > arguments, so hopefully it will only make things more permissive and > doesn't break anything. We can only hope! ;)