linux-kernel - [PATCH] kasan: Increase the number of bits to shift when recording extra timestamps

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Date: Thu, 15 Feb 2024 18:39:55 +0000
From: Juntong Deng <juntong.deng@...look.com>
To: ryabinin.a.a@...il.com,
	glider@...gle.com,
	andreyknvl@...il.com,
	dvyukov@...gle.com,
	vincenzo.frascino@....com,
	akpm@...ux-foundation.org
Cc: kasan-dev@...glegroups.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] kasan: Increase the number of bits to shift when recording extra timestamps

Fix the mistake before, I thought printk only display 99999 seconds
at max, but actually printk can display larger number of seconds.

So increase the number of bits to shift when recording the extra
timestamp (44 bits), without affecting the precision, shift it right by
9 bits, discarding all bits that do not affect the microsecond part
(nanoseconds will not be shown).

Currently the maximum time that can be displayed is 9007199.254740s,
because

11111111111111111111111111111111111111111111 (44 bits) << 9
= 11111111111111111111111111111111111111111111000000000
= 9007199.254740

Signed-off-by: Juntong Deng <juntong.deng@...look.com>
---
 mm/kasan/common.c | 2 +-
 mm/kasan/report.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 6ca63e8dda74..e7c9a4dc89f8 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -55,7 +55,7 @@ void kasan_set_track(struct kasan_track *track, depot_stack_handle_t stack)
 	u64 ts_nsec = local_clock();
 
 	track->cpu = cpu;
-	track->timestamp = ts_nsec >> 3;
+	track->timestamp = ts_nsec >> 9;
 #endif /* CONFIG_KASAN_EXTRA_INFO */
 	track->pid = current->pid;
 	track->stack = stack;
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 7afa4feb03e1..b48c768acc84 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -267,7 +267,7 @@ static void print_track(struct kasan_track *track, const char *prefix)
 	u64 ts_nsec = track->timestamp;
 	unsigned long rem_usec;
 
-	ts_nsec <<= 3;
+	ts_nsec <<= 9;
 	rem_usec = do_div(ts_nsec, NSEC_PER_SEC) / 1000;
 
 	pr_err("%s by task %u on cpu %d at %lu.%06lus:\n",
-- 
2.39.2