From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.214.171 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794513895; b=4SXKmNRFJbHMoqMLx9Zf+bazpUe6dIUWwhfQ3Y4Y2ADegFXl2r5hAVbWkQrcBOOHT1Hg 1tTXTxuZe7sAmqbEgNpDgbeV0MXmKnlQN3dwM0yHcuFM3ZUu9ezQu7xcdwH1H/ZrqVp/J Ue5714NsfXUD247VdOdvoLH0HwjpLDbOoNI6si6FOHUEspPq9jhdxanyfUqMVYGQYZWGS 1ZDBElIg0NeScwvj3KhbKqZMJ3l8XyJ5LqYyzUI7AYPNKqRVlu7GJTTUXqgkCZNw2d2a0 ruTLZv89wyD1cq4L5meuUNMly2I1ayZMxxD+GK9QqvqrrSGE3SQKM7MtQ9O9+SXdZMw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794513895; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Content-Type:Date:Message-Id:Cc:Subject:From:To:In-Reply-To: References:Content-Transfer-Encoding:MIME-Version; bh=WcAHgOOesRnpg5Fo7kmgrPBf3yTrJRhLe8HkoymNW8o=; b=E2i5dDKQ7SlC37xTJlJnu+akKkgzeAu0ONyRsGWxwwkFsyXl4jy9JEMW/6/+p1RMXRxG krDtaYlESHUynXVry04QkpEWvrBhshb7sBfbHiDI2v4i4B7CeD5EMR739z1KTa/kvlr1N W7Jr9if/qz6zEC+bfMoWIPEH0SJamhP9XMfOki59u3OJw0fDzpdzMos3DbItpyUg5++3T sDJBwCJPmFWP2RASecOhUpT6avkfZdz9ao3Qq4brmRUw7ITLqWdHT87B3JP/0EFLdRxDz zL4bBPlNQ8q5qC+up/KiJQQfeXSxslTJcV18pzGOvw8HyrCu/t3q7U0Qn+/NLkNli9w== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=vggPxoWo; arc=none smtp.remote-ip=209.85.214.171 Received: from mail-pl1-f171.google.com (mail-pl1-f171.google.com [209.85.214.171]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 95F64606A31C for ; Thu, 12 Nov 2026 20:04:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 95F64606A31C Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=vggPxoWo Received: by mail-pl1-f171.google.com with SMTP id d9443c01a7336-2e987a2ba0cso1341395ad.3 for ; Thu, 12 Nov 2026 12:04:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1794513894; x=1795118694; darn=vger.kernel.org; h=mime-version:content-transfer-encoding:references:in-reply-to:to :from:subject:cc:message-id:date:content-type:from:to:cc:subject :date:message-id:reply-to:content-type; bh=WcAHgOOesRnpg5Fo7kmgrPBf3yTrJRhLe8HkoymNW8o=; b=vggPxoWoiJ/39E89qJZJH9FH/Pf989NSXBHeza98erDwU1o04E6KcfuzghMwxyqzrq 8DBZXZvES0wlkSqPXtaZWtHFrYsS7Gm84DIAkiGqHuYJED5N4SS4iOtPr2rDTR8fE/OH SND5G9fli5Z9ZKhR/L5taQWjs6a9O5XLC7S86BCxzz4+Rk7/p7uho1Im3fDnYrDb7rpz 6fGQM6eHHQ6gZXSt/92od+AN1MoZ4Xq61XQ/AvsYfoIait3kbgDNKbw2ZOxvdKr9rojj BMS6VQr38yYO58k9M0QK0gXMc0qKx/t/q7HvC5TtiCCNxTiJKzTsmQsNaTGZ0lE6uzm1 UhIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1794513894; x=1795118694; h=mime-version:content-transfer-encoding:references:in-reply-to:to :from:subject:cc:message-id:date:content-type:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=WcAHgOOesRnpg5Fo7kmgrPBf3yTrJRhLe8HkoymNW8o=; b=tRjeGbSDTDmnVnGARjqyedqGMm5LER3//1ETa+4WhI9Q0rBISOKYZoAvIPNmwdYNvJ dth2ILNn0urCSwq/qHIaIJFsUJq+XNOoLj0KsnQijEhOm6TKwNjBPeHZSR3fl08nWqe3 3Zr02MIrYse/VCOOiUTbugOcSAH6gYaNpfzynlox74JI6a4dsAup7s0uNfatsTTMDzBG umHUW4dt3E1ZDtiHv0eOI3CSJa4zhu/kmJGhXPaQ5fyMSDsiv8LJepagYpNcohAnhqZo Xeumcz1rR8iBSzbM6wIuYo9e/icE3MsLY1BoxXWXUZVoocV/ZQb473ZrQLncw+pgS6lK 58yQ== X-Forwarded-Encrypted: i=1; AL+hErFE5ew+Yid09aAYT0gawtdlQ2GYxpkG895OnKS7x1e3UNUVGsKL0hf1tADv6I9IFiU/OSBnDvbxi/LGetg=@vger.kernel.org X-Gm-Message-State: APuU4Z+O78dAkPgxhAOWdtOQjM/nZopga1WpDnBLMev7pPTXzZKE4B75 Pgz9A12rYk5zKpfKFAIO6SPreUrwENBMmQHY0ibvJM6e3kv0u5U9Vr6Y X-Gm-Gg: AYBFou2a8hBse2fwZE/cX1S524wgoqgTu9MMSWPrEmci7gH4vu5mvFoZcPTGxGRYMP6 1t7q1QRZz0wyqklEow17SgEv0UbraJMMjY24eh4eD8Md/MMIOrvDNGNTjQd4oJxHf+a2ltgSHWh 4w8+mrcxEWksbwdwDtKNui4D6Q+JUm67r+48uffo8JM0LhMX2ekFo0M0lWy6/mq2EV1i3Nn25st IqSGIPHMHX/2yiFDYCpGhmgnjir2y/V9FYFgFmDeO8FJVjii19pN7SqtZm2ZWg4PajVHXVVxPEj 0UKn23HGkqvq6o5YYYmN63c/dpWjmX1WK2hopVRm4lZafCSILhqAuliaqDx1vXCUnlfVOW8m97B vPSrC75C4iwsY/9besJ9Ukc4gpDmVF+4bmM/96QnUOvuS7wWItYvnStWUfYsJ9PE4QsMUwGKpVq dLxGVLaY2LVo4oD2BtRYekY7/Zmc1qdM+lY2R36+aijsh3rYjHRm0pneBZpFAxoQvfgTqlDbzNt /JoUHUD/tdLIMzWSlux8vGQCbgpPWjgDXm0HOKMPc7fFcsVSYIeh0iAE/0xoVglukTNwVyj22Zr o1IT+tNp+CHPpyECE1lystA0Wq5PuIdue5lyUEfEqHKp5BQ4t0W9vJHY8zuziBBZTs1IXQ8fbR8 50NWdgQl2S89VCZHaC0hk4Nu2ygSd8pJY4A== X-Received: by 2002:a17:902:fc8d:b0:2e8:79d:15ec with SMTP id d9443c01a7336-2ee0d664b70mr4529905ad.6.1794513893558; Thu, 12 Nov 2026 12:04:53 -0800 (PST) Received: from localhost ([153.61.198.249]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ee0f75c980sm536275ad.25.2026.11.12.12.04.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Nov 2026 12:04:53 -0800 (PST) Content-Type: text/plain; charset=UTF-8 Date: Thu, 12 Nov 2026 20:04:52 +0000 Message-Id: Cc: , , "Sumit Semwal" , =?utf-8?q?Christian_K=C3=B6nig?= , "Philipp Stanner" , , , Subject: Re: [PATCH] bpf: make dmabuf iterator stay drained after NULL From: "Alexei Starovoitov" To: "Kang Chen" , "Yonghong Song" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" In-Reply-To: <20261110125106.2935677-1-k.chen@smail.nju.edu.cn> References: <20261110125106.2935677-1-k.chen@smail.nju.edu.cn> Content-Transfer-Encoding: 8bit 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 On Tue, Nov 10, 2026 at 04:51 AM Kang Chen wrote: > +/* > + * The iterator state is one pointer wide because struct bpf_iter_dmabuf is > + * part of the generated vmlinux.h ABI. Use an invalid pointer value as the > + * "drained" sentinel instead of growing the state. > + */ > +#define DMABUF_ITER_DONE ((struct dma_buf *)1L) +1 to T.J.'s point re: DMABUF_ITER_START. bpf_iter_kmem_cache_next() does it that way. dma_buf_iter_next() leaves NULL at the end of the list. Let NULL mean drained. Then no need for the 2nd store in next() and for the long comments. diff --git a/kernel/bpf/dmabuf_iter.c b/kernel/bpf/dmabuf_iter.c index cd50024..1bef87b 100644 --- a/kernel/bpf/dmabuf_iter.c +++ b/kernel/bpf/dmabuf_iter.c @@ -156,6 +156,8 @@ struct bpf_iter_dmabuf_kern { struct dma_buf *dmabuf; } __aligned(8); +#define DMABUF_ITER_START ((struct dma_buf *)1L) + __bpf_kfunc_start_defs(); __bpf_kfunc int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it) @@ -165,7 +167,7 @@ __bpf_kfunc int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it) BUILD_BUG_ON(sizeof(*kit) > sizeof(*it)); BUILD_BUG_ON(__alignof__(*kit) != __alignof__(*it)); - kit->dmabuf = NULL; + kit->dmabuf = DMABUF_ITER_START; return 0; } @@ -173,10 +175,14 @@ __bpf_kfunc struct dma_buf *bpf_iter_dmabuf_next(struct bpf_iter_dmabuf *it) { struct bpf_iter_dmabuf_kern *kit = (void *)it; - if (kit->dmabuf) - kit->dmabuf = dma_buf_iter_next(kit->dmabuf); - else + /* Once NULL is returned, next() has to keep returning NULL */ + if (!kit->dmabuf) + return NULL; + + if (kit->dmabuf == DMABUF_ITER_START) kit->dmabuf = dma_buf_iter_begin(); + else + kit->dmabuf = dma_buf_iter_next(kit->dmabuf); return kit->dmabuf; } @@ -185,7 +191,7 @@ __bpf_kfunc void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) { struct bpf_iter_dmabuf_kern *kit = (void *)it; - if (kit->dmabuf) + if (kit->dmabuf && kit->dmabuf != DMABUF_ITER_START) dma_buf_put(kit->dmabuf); } Pls take T.J.'s selftest as patch 2 and tag the respin as [PATCH bpf v2]. Also you sent fixes for css and scx_dsq. bpf_iter_task_vma_next() has the same problem. It doesn't hold mmap_lock between the calls since commit bee9ef4a40a2 ("bpf: switch task_vma iterator from mmap_lock to per-VMA locks"): Pls fix it too. pw-bot: cr