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 X-Spam-Level: X-Spam-Status: No, score=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 77E40C4727D for ; Sat, 26 Sep 2020 22:01:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3D4692388E for ; Sat, 26 Sep 2020 22:01:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727263AbgIZWBu (ORCPT ); Sat, 26 Sep 2020 18:01:50 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:34608 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726478AbgIZWBu (ORCPT ); Sat, 26 Sep 2020 18:01:50 -0400 Received: by mail-pf1-f194.google.com with SMTP id k13so6166176pfg.1 for ; Sat, 26 Sep 2020 15:01:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=QhdbG+T6+ih8CBB9tvQ+05zPjxlHN9pq9IE9yFJ/8aQ=; b=cvTSQyYG42uxgVhQxDKJTtcX+BtBpd5GMRDCEqrduLmNxANnjJcLoh0S2NNUG26H4k 4YxAmbKQOBU7cMOILnqwj0LtvRCcuRKOfkE/agA9DVmHaA+dfxUFPUXap1mpA+HPT0g8 EGRP5tEAy8IFYGRxwPyrmxswTm3jWQxE+DatYmhVqSsVpiNVSyD+qgQ54VcIzeME8kNW 1Z7m3Ur52CpzmXD3F1BIyMQoa87EHkWrZdqaPmNa/2IWmZiL4ynt29u+KQ2TTlAb4yf6 pnINbDaX9ogVh/Uc3OFz3pSCYqgUvn+pZkngP+0Prv/LR3HYr2u9qXyMDjX2meBfVvHN riWw== X-Gm-Message-State: AOAM531lpXRqdtgmNEjNxcAa/VqJMR5triuGLPzoz5jemjzZblddrmrC HZK+Gs6N3R1ERdtgLPxegjc= X-Google-Smtp-Source: ABdhPJxhWkupZ0rLNGee8A5t8TzVCTNexHAgvBOIibfej2A6WlC7XY82I9vYncSWORiYilgu9uJpMw== X-Received: by 2002:a62:7511:0:b029:142:2501:35da with SMTP id q17-20020a6275110000b0290142250135damr4918356pfc.58.1601157709084; Sat, 26 Sep 2020 15:01:49 -0700 (PDT) Received: from ?IPv6:2601:647:4000:d7:d9b2:e338:51cb:ba62? ([2601:647:4000:d7:d9b2:e338:51cb:ba62]) by smtp.gmail.com with ESMTPSA id h1sm2530116pji.52.2020.09.26.15.01.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 26 Sep 2020 15:01:48 -0700 (PDT) Subject: Re: [PATCH] scsi_dh_alua: avoid crash during alua_bus_detach() To: Hannes Reinecke , "Martin K. Petersen" Cc: Christoph Hellwig , James Bottomley , "Ewan D . Milne" , linux-scsi@vger.kernel.org, Brian Bunker References: <20200924104559.26753-1-hare@suse.de> From: Bart Van Assche Autocrypt: addr=bvanassche@acm.org; prefer-encrypt=mutual; keydata= mQENBFSOu4oBCADcRWxVUvkkvRmmwTwIjIJvZOu6wNm+dz5AF4z0FHW2KNZL3oheO3P8UZWr LQOrCfRcK8e/sIs2Y2D3Lg/SL7qqbMehGEYcJptu6mKkywBfoYbtBkVoJ/jQsi2H0vBiiCOy fmxMHIPcYxaJdXxrOG2UO4B60Y/BzE6OrPDT44w4cZA9DH5xialliWU447Bts8TJNa3lZKS1 AvW1ZklbvJfAJJAwzDih35LxU2fcWbmhPa7EO2DCv/LM1B10GBB/oQB5kvlq4aA2PSIWkqz4 3SI5kCPSsygD6wKnbRsvNn2mIACva6VHdm62A7xel5dJRfpQjXj2snd1F/YNoNc66UUTABEB AAG0JEJhcnQgVmFuIEFzc2NoZSA8YnZhbmFzc2NoZUBhY20ub3JnPokBOQQTAQIAIwUCVI67 igIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEHFcPTXFzhAJ8QkH/1AdXblKL65M Y1Zk1bYKnkAb4a98LxCPm/pJBilvci6boefwlBDZ2NZuuYWYgyrehMB5H+q+Kq4P0IBbTqTa jTPAANn62A6jwJ0FnCn6YaM9TZQjM1F7LoDX3v+oAkaoXuq0dQ4hnxQNu792bi6QyVdZUvKc macVFVgfK9n04mL7RzjO3f+X4midKt/s+G+IPr4DGlrq+WH27eDbpUR3aYRk8EgbgGKvQFdD CEBFJi+5ZKOArmJVBSk21RHDpqyz6Vit3rjep7c1SN8s7NhVi9cjkKmMDM7KYhXkWc10lKx2 RTkFI30rkDm4U+JpdAd2+tP3tjGf9AyGGinpzE2XY1K5AQ0EVI67igEIAKiSyd0nECrgz+H5 PcFDGYQpGDMTl8MOPCKw/F3diXPuj2eql4xSbAdbUCJzk2ETif5s3twT2ER8cUTEVOaCEUY3 eOiaFgQ+nGLx4BXqqGewikPJCe+UBjFnH1m2/IFn4T9jPZkV8xlkKmDUqMK5EV9n3eQLkn5g lco+FepTtmbkSCCjd91EfThVbNYpVQ5ZjdBCXN66CKyJDMJ85HVr5rmXG/nqriTh6cv1l1Js T7AFvvPjUPknS6d+BETMhTkbGzoyS+sywEsQAgA+BMCxBH4LvUmHYhpS+W6CiZ3ZMxjO8Hgc ++w1mLeRUvda3i4/U8wDT3SWuHcB3DWlcppECLkAEQEAAYkBHwQYAQIACQUCVI67igIbDAAK CRBxXD01xc4QCZ4dB/0QrnEasxjM0PGeXK5hcZMT9Eo998alUfn5XU0RQDYdwp6/kMEXMdmT oH0F0xB3SQ8WVSXA9rrc4EBvZruWQ+5/zjVrhhfUAx12CzL4oQ9Ro2k45daYaonKTANYG22y //x8dLe2Fv1By4SKGhmzwH87uXxbTJAUxiWIi1np0z3/RDnoVyfmfbbL1DY7zf2hYXLLzsJR mSsED/1nlJ9Oq5fALdNEPgDyPUerqHxcmIub+pF0AzJoYHK5punqpqfGmqPbjxrJLPJfHVKy goMj5DlBMoYqEgpbwdUYkH6QdizJJCur4icy8GUNbisFYABeoJ91pnD4IGei3MTdvINSZI5e Message-ID: <2175d8e0-88fa-a9eb-5d50-46f0eed402cf@acm.org> Date: Sat, 26 Sep 2020 15:01:46 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20200924104559.26753-1-hare@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 2020-09-24 03:45, Hannes Reinecke wrote: > alua_bus_detach() might be running concurrently with alua_rtpg_work(), > so we might trip over h->sdev == NULL and call BUG_ON(). > The correct way of handling it would be to not set h->sdev to NULL > in alua_bus_detach(), and call rcu_synchronize() before the final > delete to ensure that all concurrent threads have left the critical > section. > Then we can get rid of the BUG_ON(), and replace it with a simple > if condition. > > Cc: Brian Bunker > Signed-off-by: Hannes Reinecke > --- > drivers/scsi/device_handler/scsi_dh_alua.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c > index f32da0ca529e..308bda2e9c00 100644 > --- a/drivers/scsi/device_handler/scsi_dh_alua.c > +++ b/drivers/scsi/device_handler/scsi_dh_alua.c > @@ -658,8 +658,8 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg) > rcu_read_lock(); > list_for_each_entry_rcu(h, > &tmp_pg->dh_list, node) { > - /* h->sdev should always be valid */ > - BUG_ON(!h->sdev); > + if (!h->sdev) > + continue; > h->sdev->access_state = desc[0]; > } > rcu_read_unlock(); > @@ -705,7 +705,8 @@ static int alua_rtpg(struct scsi_device *sdev, struct alua_port_group *pg) > pg->expiry = 0; > rcu_read_lock(); > list_for_each_entry_rcu(h, &pg->dh_list, node) { > - BUG_ON(!h->sdev); > + if (!h->sdev) > + continue; > h->sdev->access_state = > (pg->state & SCSI_ACCESS_STATE_MASK); > if (pg->pref) > @@ -1147,7 +1148,6 @@ static void alua_bus_detach(struct scsi_device *sdev) > spin_lock(&h->pg_lock); > pg = rcu_dereference_protected(h->pg, lockdep_is_held(&h->pg_lock)); > rcu_assign_pointer(h->pg, NULL); > - h->sdev = NULL; > spin_unlock(&h->pg_lock); > if (pg) { > spin_lock_irq(&pg->lock); > @@ -1156,6 +1156,7 @@ static void alua_bus_detach(struct scsi_device *sdev) > kref_put(&pg->kref, release_port_group); > } > sdev->handler_data = NULL; > + synchronize_rcu(); > kfree(h); > } Hi Hannes, Do you agree that the changes in alua_bus_detach() make the changes in alua_rtpg() superfluous? How about freezing command processing for 'sdev' while detaching a device handler instead of inserting a synchronize_rcu() call in alua_bus_detach()? I'm concerned that the alua_bus_detach() changes are not sufficient to fix all possible races between detaching a device handler and the following code from the SCSI error handler: if (sdev->handler && sdev->handler->check_sense) { int rc; rc = sdev->handler->check_sense(sdev, &sshdr); if (rc != SCSI_RETURN_NOT_HANDLED) return rc; /* handler does not care. Drop down to default handling */ } Thanks, Bart.