+ kfence-replace-local_clock-with-ktime_get_boot_fast_ns.patch added to mm-unstable branch

+ kfence-replace-local_clock-with-ktime_get_boot_fast_ns.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: kfence: replace local_clock() with ktime_get_boot_fast_ns()
has been added to the -mm mm-unstable branch.  Its filename is
     kfence-replace-local_clock-with-ktime_get_boot_fast_ns.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kfence-replace-local_clock-with-ktime_get_boot_fast_ns.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Juntong Deng <juntong.deng@outlook.com>
Subject: kfence: replace local_clock() with ktime_get_boot_fast_ns()
Date: Wed, 22 Nov 2023 20:00:26 +0000

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.

Link: https://lkml.kernel.org/r/VI1P193MB0752A2F21C050D701945B62799BAA@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM
Signed-off-by: Juntong Deng <juntong.deng@outlook.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kfence/core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/kfence/core.c~kfence-replace-local_clock-with-ktime_get_boot_fast_ns
+++ a/mm/kfence/core.c
@@ -295,7 +295,7 @@ metadata_update_state(struct kfence_meta
 	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
_

Patches currently in -mm which might be from juntong.deng@outlook.com are

kasan-improve-free-meta-storage-in-generic-kasan.patch
kfence-replace-local_clock-with-ktime_get_boot_fast_ns.patch