From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-177.mta0.migadu.com (out-177.mta0.migadu.com [91.218.175.177]) (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 DE8101DE4CC for ; Fri, 21 Mar 2025 05:47:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.177 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742536034; cv=none; b=fwzEThCIcPKtPsvE5Gu50XrrqWPInpceDvCtnPvwjWkFYK5ru19pp2cEpJnxGL6XPxR2LNdHV8sQmd1fBwBtbaedNHgWXXjQSNePFFwed3T4G/gIzJLUp1ABtVsRn5A5/i1UDbvHWWJH22I05sBpIHH/9q3T6Uey8cHsixx0yhg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742536034; c=relaxed/simple; bh=zWaWLv8mZZ3c0OlGokbpvPezMRC2fFlQi9qpRM7VBoY=; h=Message-ID:Date:MIME-Version:From:Subject:To:Cc:References: In-Reply-To:Content-Type; b=qGun2XeT723L+4bromrjV3XpZlHzpB/+OIL3Ud7RWN7Cw9uTiA2wNQKhsNUD2YaG8glvXAJNRchwRzAwiS6hDbPN35mOv7UDj00SWEqp3+4/avpVEN1zyoljRXS95OvrQW8EDG8exjIKgpwGOkjFX9zA2UN3GcEzvgilqMNR0BM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=Is8WS9WC; arc=none smtp.client-ip=91.218.175.177 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="Is8WS9WC" Message-ID: <1974322e-8c30-4c01-a566-642ed2bc7086@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1742536020; h=from:from: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; bh=jkcFP/O+Z3B/eFBZgX9t3W8dn1rxY/BeKgw+K5HzFRc=; b=Is8WS9WCS7cpn+ZW8U8Ztirrs8LiXCARvLZTKBqwCREJjjVO106Y/obwqU8jG8i+jVcbc0 NYJXxiklNi+3KK5PO6x6x7f8hlvq0np5te/MH4cjlVVfZush77E5Q7V42GtBskAhF2ssG8 ljyo1OCA41BDNLGzwROgZTNgVRaHmUo= Date: Thu, 20 Mar 2025 22:46:55 -0700 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau Subject: Re: [RFC PATCH bpf-next 0/3] Avoid skipping sockets with socket iterators To: Jordan Rife Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, Daniel Borkmann , Yonghong Song , Aditi Ghag References: <20250313233615.2329869-1-jrife@google.com> <384c31a4-f0d7-449b-a7a4-2994f936d049@linux.dev> <08387a7e-55b0-4499-a225-07207453c8d5@linux.dev> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 3/18/25 5:23 PM, Jordan Rife wrote: >> imo, this is not a problem for bpf. The bpf prog has access to many fields of a >> udp_sock (ip addresses, ports, state...etc) to make the right decision. The bpf >> prog can decide if that rehashed socket needs to be bpf_sock_destroy(), e.g. the >> saddr in this case because of inet_reset_saddr(sk) before the rehash. From the >> bpf prog's pov, the rehashed udp_sock is not much different from a new udp_sock >> getting added from the userspace into the later bucket. > > As a user of BPF iterators, I would, and did, find this behavior quite > surprising. If BPF iterators make no promises about visiting each > thing exactly once, then should that be made explicit somewhere (maybe > it already is?)? I think the natural thing for a user is to assume > that an iterator will only visit each "thing" once and to write their I can see the argument that the bpf_sock_destroy() kfunc does not work as expected if the expectation is the sk will not be rehashed. Is it your use case? I am open to have another bpf_sock_destroy() kfunc to disallow the rehash but that will be different from the current udp_disconnect() behavior which will need a separate discussion. I currently don't have this use case though. > code accordingly. Using my example from before, counting the number of > sockets I destroyed, needs to be implemented differently if I might > revisit the same socket during iteration by explicitly filtering for > duplicates inside the BPF program (possibly by filtering out sockets > where the state is TCP_CLOSE, for example) or userspace. While in this > particular example it isn't all that important if I get the count > wrong, how do we know other users of BPF iterators won't make the same > assumption where repeats matter more? I still think it would be nice > if iterators themselves guaranteed exactly-once semantics but > understand if this isn't the direction you want BPF iterators to go.