Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D847C43441 for ; Wed, 28 Nov 2018 23:35:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43A572081B for ; Wed, 28 Nov 2018 23:35:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 43A572081B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=fieldses.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-nfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726876AbeK2Kid (ORCPT ); Thu, 29 Nov 2018 05:38:33 -0500 Received: from fieldses.org ([173.255.197.46]:45692 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726382AbeK2Kid (ORCPT ); Thu, 29 Nov 2018 05:38:33 -0500 Received: by fieldses.org (Postfix, from userid 2815) id 4255C8A6; Wed, 28 Nov 2018 18:35:14 -0500 (EST) Date: Wed, 28 Nov 2018 18:35:14 -0500 From: "J. Bruce Fields" To: Vasily Averin Cc: Jeff Layton , linux-nfs@vger.kernel.org, "David S. Miller" , NeilBrown , Pavel Tikhomirov Subject: Re: [PATCH 0/1] cache_head leak in sunrpc_cache_lookup() Message-ID: <20181128233514.GC24160@fieldses.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Wed, Nov 28, 2018 at 11:45:46AM +0300, Vasily Averin wrote: > Dear all, we have found memory leak on OpenVz7 node and believe it > affects mainline too. > > sunrpc_cache_lookup() removes exprired cache_head from hash, however > if it waits for reply on submitted cache_request both of them can leak > forever, nobody cleans unhashed cache_heads. > > Originally we had claim on busy loop device of stopped container, that > had executed nfs server inside. Device was kept by mount that was > detached from already destroyed mount namespace. By using crash > search we have found some structure with path struct related to our > mount. Finally we have found that it was alive svc_export struct used > by to alive cache_request, however both of them pointed to already > freed cache_detail. > > We decided that cache_detail was correctly freed during destroy of net > namespace, however svc_export with taken path struct, cache_request > and some other structures seems was leaked forever. > > This could happen only if cache_head of svc_export was removed from > hash on cache_detail before its destroy. Finally we have found that it > could happen when sunrpc_cache_lookup() removes expired cache_head > from hash. > > Usually it works correctly and cache_put(freeme) frees expired > cache_head. However in our case cache_head have an extra reference > counter from stalled cache_request. Becasue of cache_head was removed > from hash of cache_detail it cannot be found in cache_clean() and its > cache_request cannot be freed in cache_dequeue(). Memory leaks > forever, exactly like we observed. > > After may attempts we have reproduced this situation on OpenVz7 > kernel, however our reproducer is quite long and complex. > Unfortunately we still did not reproduced this problem on mainline > kernel and did not validated the patch yet. > > It would be great if someone advised us some simple way to trigger > described scenario. I think you should be able to produce hung upcalls by flushing the cache (exportfs -f), then stopping mountd, then trying to access the filesystem from a client. Does that help? > We are not sure that our patch is correct, please let us know if our > analyze missed something. It looks OK to me, but it would be helpful to have Neil's review too. I think I'd also copy some of the above into the changelog--e.g. it might be useful to document that this can manifest as a stray reference cuont on a mount. --b.