Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
From:   Stephen Brennan <stephen.s.brennan@oracle.com>
To:     Jan Kara <jack@suse.cz>
Cc:     Stephen Brennan <stephen.s.brennan@oracle.com>,
        linux-kernel@vger.kernel.org, Luis Chamberlain <mcgrof@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Amir Goldstein <amir73il@gmail.com>
Subject: [PATCH v2 2/4] fsnotify: stop walking child dentries if remaining tail is negative
Date:   Wed,  9 Feb 2022 15:14:04 -0800
Message-Id: <20220209231406.187668-3-stephen.s.brennan@oracle.com>
In-Reply-To: <20220209231406.187668-1-stephen.s.brennan@oracle.com>
References: <20220209231406.187668-1-stephen.s.brennan@oracle.com>
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?PI51jsMNHwdcu4LXXYP/SEogKXO5iIGDJV0td/RdRNWDT7lhTB4ypiJBogDn?=
 =?us-ascii?Q?gVVvkvK2B26tS1jCOfoZHh1tt89g0K6vQNXppSVZtqLkbXzL0/zOvI8p+CEX?=
 =?us-ascii?Q?yZPpqSRreDRoZ7PMAKVolHMVj2vzvUOmd7rviGZOckc1ATpmE2n9UVrrzpFM?=
 =?us-ascii?Q?OYTK/hMQ9jFyAufsbGOd/Gf2/VqXgcH9yqs0KhfsHzOKlZ3Odj3lxYqRZnWp?=
 =?us-ascii?Q?Ov9IftqTJG43jnrunNaNepAhkmrtvhSP07xCI8W0XoNF9Fb9eoW92ggaCuNo?=
 =?us-ascii?Q?G9XEv8EHe/WVjJXF7ypTAtS9LgdBQBOtZBPxCktHFRH7/fPWeIPTTwcuFii/?=
 =?us-ascii?Q?AbaOPbQWMlg12QKB2QdGpsczdHcm7SMcoVW6wmEAio101cmjV2yee19lKPnP?=
 =?us-ascii?Q?oBqZA3jdAnWHVMuj/IMMaYmKWHTs89+LeN9PO/wgmsKYEfD09hdtKFp3QZUX?=
 =?us-ascii?Q?VVk1u25c6B5VnxZnJUvSkrDFt2eDG3oDXU+iWhEwdCMXuxZZBZ6XwVlECV47?=
 =?us-ascii?Q?djoUEmUm0/wdlgy15GtrkLHcKppTiuTW5OHwxfwrJJwC9b9uHDKT2ngYrBR7?=
 =?us-ascii?Q?VxiJ9LL+5d7+jJX0LhfrMIFS4Z15uTW4TGqedgNVqMkHR5JLWl7o+iMe2s+d?=
 =?us-ascii?Q?DOqQpjtPVwupzbSXMNkjyG31hiKWuDjk02F64cZ1C0lu5zm8Wq/6R7t1sZtO?=
 =?us-ascii?Q?qndOIFFgFWt7vcotFc7s88/ywYY153xVLyzBWxQxtPWbgbxsnuOlZzwSH8B/?=
 =?us-ascii?Q?nw451ezrj3VGB1LJwpIURx+ihgZCb7lBFUw5z19XOQpALHqHe9IbVY7y+f6m?=
 =?us-ascii?Q?O3PNhPexhuZUO7YI8pDxTGZ/fS++RGSZJziNMehpT1D/okr+Bg0ZvewhL60t?=
 =?us-ascii?Q?Ros/7Na62bHPCMS9Y/6DHHQWKabi0ivqVEyAOLrhXMDEQLtBM//dN59ZDzZ4?=
 =?us-ascii?Q?Kp7z0KVgN/O09fAQHRrnhAi8SvfS2eMkGWmTNeCdk9PH1shj9mBFL6hbtsRV?=
 =?us-ascii?Q?zqVdqzsUhmRJhKx7dFQxs1QA6QcjpUUSHLdD1BylDjToyfz8cTL06GXWAU+f?=
 =?us-ascii?Q?1d7fazUkiepKAbtylYqnucNoJtcAYbmugbUiRgH3tCFhXDEqMnkfgPCWordj?=
 =?us-ascii?Q?OGnt6EllmQgNBIFC2DXgw6XbVFhAiOakCpTG70k9m4XtVvBoHkzCeUxbil8n?=
 =?us-ascii?Q?oybtJ4cwc0huccw95WYmRejQgOUa5T4yQKd8dZ8EnwJqn2QY1RibxAWxcPG/?=
 =?us-ascii?Q?oXXf4nD2LDwhsTzbdw056lrgeRv7OaQFgygXPNx/0SyNAIVoHwNWgOymJG2g?=
 =?us-ascii?Q?7+U8oFSYmJKWmmIWLuaFY4s1VdoDMhgmZOqF3W3ddO3x8QvOPWwIwW16GgHt?=
 =?us-ascii?Q?ymtT2+cF1RfXHIZfn+iSb7z+0as6RgAJWRqvl8FJGww/HA7mV/MENu3oSfwM?=
 =?us-ascii?Q?YXOnbHTYKQn/nBGVuuU41brIlKCKeJLs0wRJEOVLNYU/uBLLtrMbaibeCCHB?=
 =?us-ascii?Q?cfU/mONQcEdVdvMi3Avczb9z/W7mG8JaD5EfYHosB3LZzYwAIMsD8e7yhAJn?=
 =?us-ascii?Q?An6szCMbmpNGz82CbUqMoUtagE2wJCaoksIcLppNVHUIn/FxNhAmhJi5uWDU?=
 =?us-ascii?Q?arOAQ9nbJUkGbxPlgQvRK+puxI0TQez9y5eglID6UiY3X4pFMjjoJV5aQP3P?=
 =?us-ascii?Q?D5dZzg=3D=3D?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: b58b7fc7-1df4-4f7b-8390-08d9ec21e2f1
X-MS-Exchange-CrossTenant-AuthSource: CH2PR10MB4166.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Feb 2022 23:14:13.6742
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 3CJnvUJsFpuYQcZ906AvswoKfQLuhhKepBRQiwXC0aUJpzrmuh/lEb9w4ig0+oCZ+QCxb02vzRwQu1Br7DAJiygeMauYSh3tcVAwbpT8ySM=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLAPR10MB4884
X-Proofpoint-Virus-Version: vendor=nai engine=6300 definitions=10253 signatures=673431
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 spamscore=0 adultscore=0
 mlxlogscore=999 suspectscore=0 mlxscore=0 phishscore=0 malwarescore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000
 definitions=main-2202090121
X-Proofpoint-GUID: x1zn8pvFdr8IKE0YJmCSrFwxKZ_djL33
X-Proofpoint-ORIG-GUID: x1zn8pvFdr8IKE0YJmCSrFwxKZ_djL33
X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,RDNS_NONE,SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE
	autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
	lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

When notification starts/stops listening events from inode's children it
has to update dentry->d_flags of all positive child dentries. Scanning
may take a long time if the directory has a lot of negative child
dentries. Use the new tail negative flag to detect when the remainder of
the children are negative, and skip them. This speeds up
fsnotify/inotify watch creation, and in some extreme cases can avoid a
soft lockup, for example, with 200 million negative dentries in a single
directory:

 watchdog: BUG: soft lockup - CPU#20 stuck for 9s! [inotifywait:9528]
 CPU: 20 PID: 9528 Comm: inotifywait Kdump: loaded Not tainted 5.16.0-rc4.20211208.el8uek.rc1.x86_64 #1
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.4.1 12/03/2020
 RIP: 0010:__fsnotify_update_child_dentry_flags+0xad/0x120
 Call Trace:
  <TASK>
  fsnotify_add_mark_locked+0x113/0x160
  inotify_new_watch+0x130/0x190
  inotify_update_watch+0x11a/0x140
  __x64_sys_inotify_add_watch+0xef/0x140
  do_syscall_64+0x3b/0x90
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Co-authored-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Co-authored-by: Gautham Ananthakrishna <gautham.ananthakrishna@oracle.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
---
 fs/notify/fsnotify.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index ab81a0776ece..1f314f85f4c1 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -127,8 +127,12 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
 		 * original inode) */
 		spin_lock(&alias->d_lock);
 		list_for_each_entry(child, &alias->d_subdirs, d_child) {
-			if (!child->d_inode)
+			if (!child->d_inode) {
+				/* all remaining children are negative */
+				if (d_is_tail_negative(child))
+					break;
 				continue;
+			}
 
 			spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
 			if (watched)
-- 
2.30.2