From: Bert Karwatzki <spasswolf@web•de>
To: linux-kernel@vger•kernel.org
Cc: "Bert Karwatzki" <spasswolf@web•de>,
linux-next@vger•kernel.org,
"Thomas Weißschuh" <thomas.weissschuh@linutronix•de>,
"Thomas Gleixner" <tglx@linutronix•de>
Subject: CONFIG_DEVMEM=y breaks gettimeofday in next-20250708
Date: Wed, 9 Jul 2025 14:42:15 +0200 [thread overview]
Message-ID: <20250709124216.3011-1-spasswolf@web.de> (raw)
In-Reply-To: <20250701-vdso-auxclock-v1-6-df7d9f87b9b8@linutronix.de>
Recently I found that my RAM has an error (memtest86+ reproducibly reports
a failing address) (this error may lead to random crashes every few days).
To further investigate the issue I tried using memtester which needs access
to /dev/mem and so I recompiled linux next-20250708 with CONFIG_DEMEM=y
and found a strange and unusual side effect:
a) the time displayed by xfce is stuck at 1.1.1970 01:00 (UTC + 1)
b) most certificates in firefox-esr fail to work due to the date being 1.1.1970
(this includes www.google.de, www.duckduckgo.com, wikipedia and youtube and many more)
c) some certificates in firefox-esr still work (kernel.org, xkcd.com, www.spiegel.de)
d) the shell built-in time (and also /usr/bin/time) fail to work, e.g.
$ time sleep 5
real 0m0,000s
user 0m0,000s
sys 0m0,002s
(even though it actually take 5 seconds for this)
e) date still works correctly, e.g.
$ date
Mi 9. Jul 11:51:20 CEST 2025
f) This example program
#include <stdlib.h>
#include <stdio.h>
#include <sys/time.h>
int main()
{
int ret;
struct timeval tv;
struct timezone tz;
ret = gettimeofday(&tv, &tz);
printf("gettimeofday returns ret = %d, tv.tv_sec = %lu tv.tv_usec = %lu\n", ret, tv.tv_sec, tv.tv_usec);
return 0;
}
gives the following output on affected versions:
$
gettimeofday returns ret = 0, tv.tv_sec = 0 tv.tv_usec = 0
These errors do not occur when using v6.16-rc5 with CONFIG_DEVMEM=y, and are 100%
reproducible so are not related to the RAM error.
I bisected the issue in between
v6.16-rc5 and next-20250708 and found commit fcc8e46f768f ("vdso/gettimeofday:
Return bool from clock_gettime() helpers") as the first bad commit.
Bert Karwatzki
next parent reply other threads:[~2025-07-09 12:42 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20250701-vdso-auxclock-v1-6-df7d9f87b9b8@linutronix.de>
2025-07-09 12:42 ` Bert Karwatzki [this message]
2025-07-09 13:17 ` CONFIG_DEVMEM=y breaks gettimeofday in next-20250708 Thomas Weißschuh
2025-07-09 16:40 ` Bert Karwatzki
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