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Wed, 1 Sep 2021 08:13:30 +0000 Subject: Re: [PATCH v2 1/7] btrfs: do not call close_fs_devices in btrfs_rm_device To: Josef Bacik References: <27fa361288b46bcc0f4b1225f7c76c96ce6dbe5f.1627419595.git.josef@toxicpanda.com> Cc: kernel-team@fb.com, linux-btrfs@vger.kernel.org From: Anand Jain Message-ID: <649d8f42-49db-69b4-45df-d0d502d7db7a@oracle.com> Date: Wed, 1 Sep 2021 16:13:23 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 In-Reply-To: <27fa361288b46bcc0f4b1225f7c76c96ce6dbe5f.1627419595.git.josef@toxicpanda.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SG2PR06CA0204.apcprd06.prod.outlook.com (2603:1096:4:1::36) To DM6PR10MB4123.namprd10.prod.outlook.com (2603:10b6:5:210::10) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.10.109] (39.109.186.25) by SG2PR06CA0204.apcprd06.prod.outlook.com (2603:1096:4:1::36) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4478.19 via Frontend Transport; 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However > we do not need to call close_fs_devices(), because at this point there > are no devices left to close as we've closed the last one. The only > thing that close_fs_devices() does is decrement ->opened, which should > be 1. We want to avoid calling close_fs_devices() here because it has a > lockdep_assert_held(&uuid_mutex), and we are going to stop holding the > uuid_mutex in this path. > > So add an assert for the ->opened counter and simply decrement it like > we should, and then clean up like normal. Also add a comment explaining > what we're doing here as I initially removed this code erroneously. > > Signed-off-by: Josef Bacik > --- > fs/btrfs/volumes.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 86846d6e58d0..5217b93172b4 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -2200,9 +2200,17 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path, > synchronize_rcu(); > btrfs_free_device(device); > > + /* > + * This can happen if cur_devices is the private seed devices list. We > + * cannot call close_fs_devices() here because it expects the uuid_mutex > + * to be held, but in fact we don't need that for the private > + * seed_devices, we can simply decrement cur_devices->opened and then > + * remove it from our list and free the fs_devices. > + */ > if (cur_devices->open_devices == 0) { We should in fact use cur_devices->num_devices == 0 here. Sent a patch [1] to fix it. [1] https://patchwork.kernel.org/project/linux-btrfs/patch/d9c89b1740a876b3851fcf358f22809aa7f1ad2a.1630478246.git.anand.jain@oracle.com/ > + ASSERT(cur_devices->opened == 1); We don't need to assert(). free_fs_devices() has a warning for it. WARN_ON(fs_devices->opened); > list_del_init(&cur_devices->seed_list); > - close_fs_devices(cur_devices); > + cur_devices->opened--; > free_fs_devices(cur_devices); > } With the above two fixed. Reviewed-by: Anand Jain Thanks, Anand