From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BE8B2C433FE for ; Thu, 17 Nov 2022 13:31:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234510AbiKQNbr (ORCPT ); Thu, 17 Nov 2022 08:31:47 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234545AbiKQNbq (ORCPT ); Thu, 17 Nov 2022 08:31:46 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 853A871F00 for ; Thu, 17 Nov 2022 05:30:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668691844; 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: in-reply-to:in-reply-to:references:references; bh=3RAbJCl/fhcop9wct6HLY/Xc5cASW2kdLAtpYvmNUTU=; b=Ek66jzDZlkQ45RKgXYAbuvypwqv48eae7/ocNxTAv8/EZRnA/5Rr4QdlZEuvxqzQx4pgMp 040CsyeCf92A1vBqIJXa1hLipYQzUtdctlXHMw5DluDtyalFkV/0n41IPP/q3TPRwdd3vg k7dhL/dlc267IVu64tkoQQsXaGp3jaY= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-537-N1_wWIDOMqem0Z8OZM_0yA-1; Thu, 17 Nov 2022 08:30:41 -0500 X-MC-Unique: N1_wWIDOMqem0Z8OZM_0yA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 1BD063C0D180; Thu, 17 Nov 2022 13:30:41 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3E55F40C6EC3; Thu, 17 Nov 2022 13:30:40 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20221117115023.1350181-2-dwysocha@redhat.com> References: <20221117115023.1350181-2-dwysocha@redhat.com> <20221117115023.1350181-1-dwysocha@redhat.com> To: Dave Wysochanski Cc: dhowells@redhat.com, Daire Byrne , Benjamin Maynard , linux-cachefs@redhat.com, linux-nfs@vger.kernel.org Subject: Re: [PATCH 1/1] fscache: Fix oops due to race with cookie_lru and use_cookie MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3715747.1668691837.1@warthog.procyon.org.uk> Date: Thu, 17 Nov 2022 13:30:37 +0000 Message-ID: <3715748.1668691837@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org Dave Wysochanski wrote: > If a cookie expires from the LRU and the LRU_DISCARD flag is set, > but the state machine has not run yet, it's possible another thread > can call fscache_use_cookie and begin to use it. When the > cookie_worker finally runs, it will see the LRU_DISCARD flag set, > transition the cookie->state to LRU_DISCARDING, which will then > withdraw the cookie. Once the cookie is withdrawn the object is > removed the below oops will occur because the object associated > with the cookie is now NULL. > > Fix the oops by clearing the LRU_DISCARD bit if another thread > uses the cookie before the cookie_worker runs. I think this is the right approach. The state machine should just fall through without doing anything, despite having been woken. David