From: "Mickaël Salaün" <mic@digikod.net>
To: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>,
Jason Gunthorpe <jgg@ziepe.ca>,
Miroslav Lichvar <mlichvar@redhat.com>,
John Stultz <john.stultz@linaro.org>,
Prarit Bhargava <prarit@redhat.com>,
Alessandro Zummo <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch 1/8] rtc: mc146818: Prevent reading garbage - bug
Date: Tue, 26 Jan 2021 15:17:40 +0100 [thread overview]
Message-ID: <98cb59e8-ecb4-e29d-0b8f-73683ef2bee7@digikod.net> (raw)
In-Reply-To: <871re7hlsg.fsf@nanos.tec.linutronix.de>
Thanks for the fix! It boots now with a new message:
rtc_cmos rtc_cmos: not accessible
I tested with rtc=on and rtc=off (which didn't make a difference before
this fix) on a microvm:
https://github.com/qemu/qemu/blob/master/docs/system/i386/microvm.rst
There is one issue with the memset though:
On 26/01/2021 14:26, Thomas Gleixner wrote:
> On Mon, Jan 25 2021 at 19:40, Mickaël Salaün wrote:
>> After some bisecting, I found that commit 05a0302c3548 ("rtc: mc146818:
>> Prevent reading garbage", this patch, introduced since v5.11-rc1) makes
>> my VM hang at boot. Before this commit, I got this (and didn't notice)
>> at every boot:
>> rtc_cmos rtc_cmos: registered as rtc0
>> rtc_cmos rtc_cmos: hctosys: unable to read the hardware clock
>> rtc_cmos rtc_cmos: alarms up to one day, 114 bytes nvram
>>
>> I notice that this patch creates infinite loops, which my VM falls into
>> (cf. below).
>>> + time->tm_sec = CMOS_READ(RTC_SECONDS);
>>> +
>>> + if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP) {
>>> + spin_unlock_irqrestore(&rtc_lock, flags);
>>> + mdelay(1);
>>
>> My VM loops here.
>> time->tm_sec is always 255.
>
> That means there is no RTC and therefore the CMOS_READ($REG) returns
> 0xFF which makes the loop stuck because RTC_UIP is always set.
>
> Yet another proof that VIRT creates more problems than it solves.
>
> Fix below.
>
> Thanks,
>
> tglx
> ---
> Subject: rtc: mc146818: Detect and handle broken RTCs
> From: Thomas Gleixner <tglx@linutronix.de>
> Date: Tue, 26 Jan 2021 11:38:40 +0100
>
> The recent fix for handling the UIP bit unearthed another issue in the RTC
> code. If the RTC is advertised but the readout is straight 0xFF because
> it's not available, the old code just proceeded with crappy values, but the
> new code hangs because it waits for the UIP bit to become low.
>
> Add a sanity check in the RTC CMOS probe function which reads the RTC_VALID
> register (Register D) which should have bit 0-6 cleared. If that's not the
> case then fail to register the CMOS.
>
> Add the same check to mc146818_get_time(), warn once when the condition
> is true and invalidate the rtc_time data.
>
> Reported-by: Mickaël Salaün <mic@digikod.net>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> drivers/rtc/rtc-cmos.c | 8 ++++++++
> drivers/rtc/rtc-mc146818-lib.c | 7 +++++++
> 2 files changed, 15 insertions(+)
>
> --- a/drivers/rtc/rtc-cmos.c
> +++ b/drivers/rtc/rtc-cmos.c
> @@ -805,6 +805,14 @@ cmos_do_probe(struct device *dev, struct
>
> spin_lock_irq(&rtc_lock);
>
> + /* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
> + if ((CMOS_READ(RTC_VALID) & 0x7f) != 0) {
> + spin_unlock_irq(&rtc_lock);
> + dev_warn(dev, "not accessible\n");
> + retval = -ENXIO;
> + goto cleanup1;
> + }
> +
> if (!(flags & CMOS_RTC_FLAGS_NOFREQ)) {
> /* force periodic irq to CMOS reset default of 1024Hz;
> *
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -21,6 +21,13 @@ unsigned int mc146818_get_time(struct rt
>
> again:
> spin_lock_irqsave(&rtc_lock, flags);
> + /* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
> + if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x7f) != 0)) {
> + spin_unlock_irqrestore(&rtc_lock, flags);
> + memset(time, 0xff, sizeof(time));
This should be: sizeof(*time)
> + return 0;
> + }
> +
> /*
> * Check whether there is an update in progress during which the
> * readout is unspecified. The maximum update time is ~2ms. Poll
>
Tested-by: Mickaël Salaün <mic@linux.microsoft.com>
next prev parent reply other threads:[~2021-01-26 14:20 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-06 21:46 [patch 0/8] ntp/rtc: Fixes and cleanups Thomas Gleixner
2020-12-06 21:46 ` [patch 1/8] rtc: mc146818: Prevent reading garbage Thomas Gleixner
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2021-01-25 18:40 ` [patch 1/8] rtc: mc146818: Prevent reading garbage - bug Mickaël Salaün
2021-01-26 13:26 ` Thomas Gleixner
2021-01-26 14:17 ` Mickaël Salaün [this message]
2021-01-26 15:35 ` Thomas Gleixner
2021-01-26 17:02 ` [PATCH V2] rtc: mc146818: Detect and handle broken RTCs Thomas Gleixner
2021-01-26 18:00 ` Alexandre Belloni
2021-01-27 8:41 ` [tip: timers/urgent] " tip-bot2 for Thomas Gleixner
[not found] ` <ghft2hwevu.fsf@gouders.net>
2021-02-01 13:53 ` [PATCH V2] " Serge Belyshev
2021-02-01 19:09 ` [PATCH] rtc: mc146818: Dont test for bit 0-5 in Register D Thomas Gleixner
2021-02-01 19:24 ` [PATCH V2] " Thomas Gleixner
2021-02-01 19:32 ` Linus Torvalds
2021-02-01 19:40 ` Thomas Gleixner
2021-02-11 23:09 ` Maciej W. Rozycki
2021-02-01 19:38 ` Alexandre Belloni
2021-02-01 20:09 ` Borislav Petkov
2021-02-01 20:15 ` Dirk Gouders
2021-02-02 4:22 ` Len Brown
2021-02-02 19:40 ` [tip: timers/urgent] " tip-bot2 for Thomas Gleixner
2021-02-03 13:00 ` [PATCH V2] " Mickaël Salaün
2020-12-06 21:46 ` [patch 2/8] rtc: mc146818: Reduce spinlock section in mc146818_set_time() Thomas Gleixner
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-12-06 21:46 ` [patch 3/8] rtc: cmos: Make rtc_cmos sync offset correct Thomas Gleixner
2020-12-07 20:50 ` Jason Gunthorpe
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-12-06 21:46 ` [patch 4/8] rtc: core: Make the sync offset default more realistic Thomas Gleixner
2020-12-07 20:55 ` Jason Gunthorpe
2020-12-10 23:59 ` Alexandre Belloni
2020-12-11 0:23 ` Thomas Gleixner
2020-12-11 0:28 ` Alexandre Belloni
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-12-06 21:46 ` [patch 5/8] ntp: Make the RTC synchronization more reliable Thomas Gleixner
2020-12-07 12:47 ` Miroslav Lichvar
2020-12-07 20:59 ` Jason Gunthorpe
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-12-29 19:41 ` [patch 5/8] " Geert Uytterhoeven
2021-01-11 10:12 ` Thomas Gleixner
2021-01-11 10:40 ` Geert Uytterhoeven
2020-12-06 21:46 ` [patch 6/8] ntp, rtc: Move rtc_set_ntp_time() to ntp code Thomas Gleixner
2020-12-07 20:59 ` Jason Gunthorpe
2020-12-09 3:51 ` Alexandre Belloni
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-12-06 21:46 ` [patch 7/8] ntp: Make the RTC sync offset less obscure Thomas Gleixner
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-12-06 21:46 ` [patch 8/8] ntp: Consolidate the RTC update implementation Thomas Gleixner
2020-12-07 21:05 ` Jason Gunthorpe
2020-12-11 9:23 ` Thomas Gleixner
2020-12-11 10:07 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2020-12-09 0:33 ` [patch 0/8] ntp/rtc: Fixes and cleanups Thomas Gleixner
2020-12-09 4:01 ` Alexandre Belloni
2020-12-09 12:39 ` Thomas Gleixner
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