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 10ABB2FA3E for ; Thu, 20 Jul 2023 17:12:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 20CDEC433C8; Thu, 20 Jul 2023 17:12:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689873152; bh=zts5NGHn5WQO6o2e+6B3ydRceosp6xQJd00HqAw+IqY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=MGgQOpn/VZvgDzWlCQN9LvoD1UVj9oGVDzUyA3BzkG8l0/DDAKaasuWhF+jmTBwMP YgzWR2xlknaz/X5CbhkIIAM5GtDSv5WiO51OqlwYHFA+QIC8TjW6XF3Ikex7J3jVWm C/tA19VEADT/7ZnAV49R+vV5cAlrVIxy8LYJAR7fC4vBDkOt8xj9FR+6Kgw9lieP1K 6kC2/2BmnR1sX2CVDRbpiAE8xFQV/Wpb99OWsgaSQ7hIzSi3i0EyMcecBdrEhost88 bmeThMTvqtp9uuZsy9MvD09bPob5spz9okpkSRP6yomR+frUdgyV/nBMdkW+sG53VN zY8N1jsB/Qicg== Date: Thu, 20 Jul 2023 10:12:31 -0700 From: Jakub Kicinski To: Alexander Lobakin Cc: "David S. Miller" , Eric Dumazet , Paolo Abeni , Maciej Fijalkowski , Larysa Zaremba , Yunsheng Lin , Alexander Duyck , Jesper Dangaard Brouer , "Ilias Apalodimas" , , Subject: Re: [PATCH RFC net-next v2 7/7] net: skbuff: always try to recycle PP pages directly when in softirq Message-ID: <20230720101231.7a5ff6cd@kernel.org> In-Reply-To: <48c1d70b-d4bd-04c0-ab46-d04eaeaf4af0@intel.com> References: <20230714170853.866018-1-aleksander.lobakin@intel.com> <20230714170853.866018-10-aleksander.lobakin@intel.com> <20230718174042.67c02449@kernel.org> <20230719135150.4da2f0ff@kernel.org> <48c1d70b-d4bd-04c0-ab46-d04eaeaf4af0@intel.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 20 Jul 2023 18:46:02 +0200 Alexander Lobakin wrote: > From: Jakub Kicinski > Date: Wed, 19 Jul 2023 13:51:50 -0700 > > > On Wed, 19 Jul 2023 18:34:46 +0200 Alexander Lobakin wrote: > [...] > >> > >> If we're on the same CPU where the NAPI would run and in the same > >> context, i.e. softirq, in which the NAPI would run, what is the problem? > >> If there really is a good one, I can handle it here. > > > > #define SOFTIRQ_BITS 8 > > #define SOFTIRQ_MASK (__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT) > > # define softirq_count() (preempt_count() & SOFTIRQ_MASK) > > #define in_softirq() (softirq_count()) > > I do remember those, don't worry :) > > > I don't know what else to add beyond that and the earlier explanation. > > My question was "how can two things race on one CPU in one context if it > implies they won't ever happen simultaneously", but maybe my zero > knowledge of netcons hides something from me. One of them is in hardirq. > > AFAIK pages as allocated by page pool do not benefit from the usual > > KASAN / KMSAN checkers, so if we were to double-recycle a page once > > a day because of a netcons race - it's going to be a month long debug > > for those of us using Linux in production. > > if (!test_bit(&napi->state, NPSVC)) if you have to the right check is !in_hardirq() > ? It would mean we're not netpolling. > Otherwise, if this still is not enough, I'do go back to my v1 approach > with having a NAPI flag, which would tell for sure we're good to go. I > got confused by your "wouldn't just checking for softirq be enough"! T.T > Joking :D I guess the problem I'm concerned about can already happen. I'll send a lockdep annotation shortly.