From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B190E21A4BB for ; Fri, 25 Oct 2024 15:26:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729870009; cv=none; b=Z9zvZZ2IIuVesb6i2hxG330awL+N2jyXnPHAgwq6Fa0e5LrEYSPIHvkGzOW7mLis144b2Uxf9aC6hMQgkgXpagupg0BlnB/TFVL9OLlpj53hnLNnqstrEWUNHD21/F434IWIIjLf6pyLv7R109NQCI9MfRSCVxB7mRgOlxdGHCY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729870009; c=relaxed/simple; bh=Tq4NRwP1OhYsfT6k2oMrKq8ECS66eXRRkxu5+shtEXQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Wvu7r1euibZCIDd33h6vpjdgt2OsOdujkKvC/zB5nnhGBCZT/cNUplNi5Vyt0pNFd5c6Wm+gkg31ML6satNnFdv/IH0pCeCOSxkBFZirFN7Gy3kaIJydxs5TNryVyTcCDFxrP9jnV332x3KpA6J15BdLpStZZTY8jV2hZyje4/Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Amcqb9Y7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Amcqb9Y7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61ECEC4CEC3; Fri, 25 Oct 2024 15:26:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729870009; bh=Tq4NRwP1OhYsfT6k2oMrKq8ECS66eXRRkxu5+shtEXQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Amcqb9Y7BzPd2/HHzkYTlCzYheSVWWV3Qs9h1GkBLXN8f8hYgyy9rl+Qp5xThOTZb j6bTUkcrSNBDPtmqGmDU31EbR1MeTdtckLmDzja8WwLD+itKMfD/xLMOXJaAn3jAs5 xnfbSnqsJ1hx3xtJYb0T2DvY1BJpBvL7oCEuF2gnaQak7qt58/vMuRQAvI8puofKOu IbL+NsmwI6GfBng3xnZ+OJK9kP9nYqYRemRQS/aDkFsDdKezurEz5rRbGpRPO+lgu5 4mu5ZBHMDxISW25IAa6LCzjCWS56jo4u5Ov7imh6RwwX3cIc+kKINfBUCE9GghZVTP aMZPtZXWdDepg== Message-ID: Date: Fri, 25 Oct 2024 17:26:46 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-net v2 2/3] mptcp: pm: lockless list traversal Content-Language: en-GB To: Geliang Tang , mptcp@lists.linux.dev Cc: Paolo Abeni References: <20241025-mptcp-pm-lookup_addr_rcu-v2-0-1478f6c4b205@kernel.org> <20241025-mptcp-pm-lookup_addr_rcu-v2-2-1478f6c4b205@kernel.org> <48c030b9f5156dddec50e8727062b8350a53f8a0.camel@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Geliang, Thank you for the review! On 25/10/2024 16:25, Geliang Tang wrote: > On Fri, 2024-10-25 at 11:32 +0200, Matthieu Baerts (NGI0) wrote: >> In a few places -- to get an endpoint, dump all of them, and change >> their flags -- the list is iterated while holding the pernet->lock, >> but >> only to read the content of the list. In these cases, we can replace >> the >> spin locks, by RCU read ones, and use the _rcu variants to iterate >> over >> the entries list in a lockless way. >> >> To make it clear, the lookup helpers using the _rcu variant are >> renamed >> with a _rcu suffix. The previous __lookup_addr() helper can then be >> removed, but __lookup_addr_by_id() is still needed. >> >> While at it, the IDs bitmap is copied before iterating the list to >> dump >> the different addresses, to avoid any consistencies. >> >> Signed-off-by: Matthieu Baerts (NGI0) >> --- >> Notes: >>  - This is not a fix, a small improvement for -next. >> --- >>  net/mptcp/pm_netlink.c | 36 +++++++++++++++++++----------------- >>  1 file changed, 19 insertions(+), 17 deletions(-) >> >> diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c >> index >> a93b9b7776b48781a883673fe5fd521a978487ff..f38e1ccd34e95cd88b179a8b50e >> 6965731542871 100644 >> --- a/net/mptcp/pm_netlink.c >> +++ b/net/mptcp/pm_netlink.c (...) >> @@ -1872,16 +1872,18 @@ int mptcp_pm_nl_dump_addr(struct sk_buff >> *msg, >>   struct net *net = sock_net(msg->sk); >>   struct mptcp_pm_addr_entry *entry; >>   struct pm_nl_pernet *pernet; >> + unsigned long id_bitmap[4]; >>   int id = cb->args[0]; >>   void *hdr; >>   int i; >>   >>   pernet = pm_nl_get_pernet(net); >> + bitmap_copy(id_bitmap, pernet->id_bitmap, >> MPTCP_PM_MAX_ADDR_ID + 1); > > I think the id bitmap should only be copied when id is 0: > > if (!id) > bitmap_copy(id_bitmap, pernet->id_bitmap, MPTCP_PM_MAX_ADDR_ID + 1); > > Since this mptcp_pm_nl_dump_addr() may be called repeatedly when the > dump information is very long. We only copy it the first time it is > called, and subsequent calls cannot copy it again. WDYT? Sorry, I'm not sure to understand. Here, I did a local copy of 'id_bitmap' just to keep a certain consistency if the bitmap is changed during the RCU read section below: not to have this bitmap being changed during the for loop here below. Before, we had this protection because pernet->lock was held. Are you suggesting here to keep a copy in the cb, not a local one, to do the copy only once? Are you sure it is worth it (and safe)? >>   >> - spin_lock_bh(&pernet->lock); >> + rcu_read_lock(); >>   for (i = id; i < MPTCP_PM_MAX_ADDR_ID + 1; i++) { >> - if (test_bit(i, pernet->id_bitmap)) { >> - entry = __lookup_addr_by_id(pernet, i); >> + if (test_bit(i, id_bitmap)) { >> + entry = __lookup_addr_by_id_rcu(pernet, i); >>   if (!entry) >>   break; >>   Cheers, Matt -- Sponsored by the NGI0 Core fund.