Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:7 as permitted sender) client-ip=2620:137:e000::3:7;
From:   Juntong Deng <juntong.deng@outlook.com>
To:     glider@google.com, elver@google.com, dvyukov@google.com,
        akpm@linux-foundation.org
Cc:     kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org
Subject: [PATCH] kfence: Replace local_clock() with ktime_get_boot_fast_ns()
Date:   Wed, 22 Nov 2023 20:00:26 +0000
Message-ID: <VI1P193MB0752A2F21C050D701945B62799BAA@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM>
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
MIME-Version: 1.0
X-MS-Exchange-MessageSentRepresentingType: 1
X-MS-PublicTrafficType: Email
X-MS-TrafficTypeDiagnostic: VI1P193MB0752:EE_|AM8P193MB1107:EE_
X-MS-Office365-Filtering-Correlation-Id: ef9e6723-a192-4f11-f7ae-08dbeb95c9e2
X-Microsoft-Antispam: BCL:0;
X-Microsoft-Antispam-Message-Info: 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
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?Eth6GuGvWtSiV7pZfMXjwvMT9vDzXPBrOtul90+uwKNpIdxDjqAJDOSK0fh9?=
 =?us-ascii?Q?TJs0KqaOg2yBbJWG7Yem4LJ3WDxKIZAn8e3JYBOmFzHzws3PAvqnePAtzzIZ?=
 =?us-ascii?Q?L1QY+QkUtTSFgjBKZgEKAOTfuG3Bpyxl6YgAejUEgRwQM+/VXxDi7C236Yvv?=
 =?us-ascii?Q?PFaz6aRyQwiJtKphARUdda2M9QrgoJeHigJPGPzZlFbeW9iXaUpinyIYTt00?=
 =?us-ascii?Q?U38Zkae+NkBwU5cyLNWb+sW4pZeruc8yEfDZpLuAbw35YhQeXiYzPxn6u0WQ?=
 =?us-ascii?Q?0WIaz6Z6va+2ks+071KU1CATwLOSN22/F51O4FR1dx0M5NehKilNZE59P52d?=
 =?us-ascii?Q?BXUVevCLEdPs7t8zxNFDiRFY5EZ2Ks98ZIxDb31/UHT5BGVJoTK3Vty+U4Rp?=
 =?us-ascii?Q?burBJj7WPbEfEWrxn1c48F8LzOUCQuHW7rTDQMAxiLjjppec/DT6VjfSDDag?=
 =?us-ascii?Q?BwFrESAvaX6jkxGpCUCIcRmXTAyYNeLuI4sFqc7mzDmUFllofx6jWJ0nvGJi?=
 =?us-ascii?Q?HzNUkCn2R3I0fG+ik08g+0Aaes3uBo2vG4/Brj8Jy+HlPHS1AxWj1D5pFE8I?=
 =?us-ascii?Q?Ct0/W1U8nvSM6PZhnWGZAmVd5VGiMTnSiGsuPGf5bN0RJGCZ4pg5BDfHhXhU?=
 =?us-ascii?Q?qqaj1oJzO/+X+EB+rHKjf528WUX3Dwwwgyfytos1mQuSQrvxvqrvn+YonnFl?=
 =?us-ascii?Q?DPV24MZgiMXucc9RAMAHiwWiDm2u0x/SSA0lrWlb+bjJx1QeXVeHI4StvuD5?=
 =?us-ascii?Q?b2xDetXCHqlbpRZZuBKE/VxUB3ZJ3mbfWvrvbOV/F6OhoUOdUoEw0gJT1KzT?=
 =?us-ascii?Q?UbSI+bVpmQdzt74w2QPb+J8L6CiumS5b1iriS3RplqIVcud09h6hrO/YAD0R?=
 =?us-ascii?Q?jA+2x+CMmnGOjMfqidpCQjqDnC8RVp7SeKOfPDT7zKa50/Q0Y0rG+grzhSU0?=
 =?us-ascii?Q?rmAlUu6vG8rgDPWLeAhioxwtIjXR2t1G0zF8qEcfz1WZ7fqhrCI0wJWOP48R?=
 =?us-ascii?Q?J6gJaaRPesxN6kPO+4i3TJ1qNcyLZeGuWKLkMHyLxi/79vNox06FuAwVGsgl?=
 =?us-ascii?Q?Ou1XoKr0eqVXBi/UVNLOmdGzOzyBBIsAe2nshn0B0rPtQPHtcpWb52HhWgDO?=
 =?us-ascii?Q?gZz+EGrkbEpDL2MAxpaEENBlksuQ/XA5H5ypzcX40FBT3kU93oL8k1tzNO4w?=
 =?us-ascii?Q?bL7ZRsUpOPcFHLFQU5CwnxClflFwd7dLFWgtXRQEffQZVXBmrHSM07xcGcc?=
 =?us-ascii?Q?=3D?=
X-OriginatorOrg: outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: ef9e6723-a192-4f11-f7ae-08dbeb95c9e2
X-MS-Exchange-CrossTenant-AuthSource: VI1P193MB0752.EURP193.PROD.OUTLOOK.COM
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Nov 2023 20:01:17.6566
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM8P193MB1107
X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,
        RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_PASS,
        T_SCC_BODY_TEXT_LINE autolearn=ham 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
X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Wed, 22 Nov 2023 12:01:28 -0800 (PST)

The time obtained by local_clock() is the local CPU time, which may
drift between CPUs and is not suitable for comparison across CPUs.

It is possible for allocation and free to occur on different CPUs,
and using local_clock() to record timestamps may cause confusion.

ktime_get_boot_fast_ns() is based on clock sources and can be used
reliably and accurately for comparison across CPUs.

Signed-off-by: Juntong Deng <juntong.deng@outlook.com>
---
 mm/kfence/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 3872528d0963..041c03394193 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -295,7 +295,7 @@ metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state nex
 	track->num_stack_entries = num_stack_entries;
 	track->pid = task_pid_nr(current);
 	track->cpu = raw_smp_processor_id();
-	track->ts_nsec = local_clock(); /* Same source as printk timestamps. */
+	track->ts_nsec = ktime_get_boot_fast_ns();
 
 	/*
 	 * Pairs with READ_ONCE() in
-- 
2.39.2