Received: by 2002:ac0:a5a7:0:0:0:0:0 with SMTP id m36-v6csp1850555imm; Sun, 15 Jul 2018 19:17:53 -0700 (PDT) X-Google-Smtp-Source: AAOMgpfUvf78FWiAvc5Gom0a2yOhNOaPtJROTzmeqqsn6oxX/Fa9NUzwraPtJjIWqFVkgG0LG1Yf X-Received: by 2002:aa7:800f:: with SMTP id j15-v6mr5042288pfi.174.1531707473546; Sun, 15 Jul 2018 19:17:53 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1531707473; cv=none; d=google.com; s=arc-20160816; b=vrcyuYeymzG4jVjBfihJMwdYH5T18khveau+QWD8n7JRQBRz2dzVBi/gmNJYHAubfb 1LhkQ4J1WHBW9It9GxgEy1sjKX1msFeZRByq5PFzohkzij+w7wm8pwG5c6DSREgGR6LX 4Ygyab9EFI3WoaKNyR4oDlRG4K3OG3FuY/tspfGrdTf+ew+RI/2av+bDF/f2vvqUkg0q /6V4og8lbLSjpMXbZXSNaw00kLIlmEIbBm3PMSRbCL3MpEOn1w2rgmarBpKWO4eRA7v3 bGv4zEq0ZhXxRQ3bmXlfsmmq/EsLB+j9q3rOlGPa9a5oRLogY5JodSkbSiBj4i2atcEC prjw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:user-agent:in-reply-to :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:arc-authentication-results; bh=hqj90VOTVVW17bOxXt+gNlo7PSihpVMx0OUZv+nQ58A=; b=s9z640OfQfwt3GO2EPP9WVGA2+kel/9D3KX7WHVsuHybqBfmek3BbMxmWBGSPS8Ifa 8k4ER79h2RGkuRfojFBnLC0fMDHMrAmLEgxyKgnvolKk9RT3ljQoF9dpRETWadL1RHtw jkkKh7wixQYkIhiFWxEBFsz1+kXpkwqPLJMwudsktC3jC2bnHbfEo1CkSdkHdxOQDDXb foOwhxDls30zui5y5X9k4XWafKWv790mfL7qjSh/2bCBRXBlMcve6ngb2f7rckYS4CiP EFhWUXc+pUGdTv1JffY55IiTNrrFo3ZiWUF5fZk4sA37+bnLwOLLU/7ht3RSRWnU4acH EWMw== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id c17-v6si27957366pge.273.2018.07.15.19.17.38; Sun, 15 Jul 2018 19:17:53 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727620AbeGPCmJ (ORCPT + 99 others); Sun, 15 Jul 2018 22:42:09 -0400 Received: from orcrist.hmeau.com ([104.223.48.154]:34542 "EHLO deadmen.hmeau.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727296AbeGPCmI (ORCPT ); Sun, 15 Jul 2018 22:42:08 -0400 Received: from gondobar.mordor.me.apana.org.au ([192.168.128.4] helo=gondobar) by deadmen.hmeau.com with esmtps (Exim 4.89 #2 (Debian)) id 1fet4M-0003I9-Ol; Mon, 16 Jul 2018 10:16:58 +0800 Received: from herbert by gondobar with local (Exim 4.89) (envelope-from ) id 1fet4H-0001ux-Mp; Mon, 16 Jul 2018 10:16:53 +0800 Date: Mon, 16 Jul 2018 10:16:53 +0800 From: Herbert Xu To: NeilBrown Cc: David Miller , tgraf@suug.ch, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, eric.dumazet@gmail.com Subject: Re: [PATCH - revised] rhashtable: detect when object movement might have invalidated a lookup Message-ID: <20180716021653.xtbyetdfc2uzxub3@gondor.apana.org.au> References: <20180601160613.7ud25g2ux55k3bma@gondor.apana.org.au> <87k1q8yh70.fsf@notabene.neil.brown.name> <20180711.224658.2077863065492745521.davem@davemloft.net> <20180711.224801.1129067473269289703.davem@davemloft.net> <87fu0kt5m0.fsf@notabene.neil.brown.name> <20180716005134.q4rfkfn3m5zzwt62@gondor.apana.org.au> <874lh0t1ls.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874lh0t1ls.fsf@notabene.neil.brown.name> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 16, 2018 at 11:23:43AM +1000, NeilBrown wrote: > > kmem_cache_free() directly. For this, I need rhashtable to be safe if > an object is deleted and immediately re-inserted into the same hash > chain. This means that rcu_read_lock(); A = rhashtable_lookup(); use(A); rcu_read_unlock(); A can turn into object B when it is used. That is just too strange for words. Can we see some actual code on how this works? For comparison, the existing net code where this happens A doesn't actually change and it simply moves from one hashtable to another. I'm relucant to add semantics that would restrain on how rhashtable works unless we have real and valid use-cases for it. Cheers, -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt