From: Lukasz Stelmach <l.stelmach@samsung.com>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: "Alessandro Zummo" <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org,
"Bartłomiej Żolnierkiewicz" <b.zolnierkie@samsung.com>,
"Marek Szyprowski" <m.szyprowski@samsung.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rtc: ds1307: set uie_unsupported if no interrupt is available
Date: Tue, 30 Mar 2021 08:52:08 +0200 [thread overview]
Message-ID: <dleftj8s65gmlj.fsf%l.stelmach@samsung.com> (raw)
In-Reply-To: <YGJqfVFVb7Z1LBTu@piout.net> (Alexandre Belloni's message of "Tue, 30 Mar 2021 02:02:05 +0200")
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It was <2021-03-30 wto 02:02>, when Alexandre Belloni wrote:
> On 16/03/2021 19:04:14+0100, Lukasz Stelmach wrote:
>> OK, you are right. The problem seems to be elsewhere.
>>
>> How about this scnario? We call rtc_update_irq_enable(). We read rtc
>> with __rtc_read_time() and calculate the alarm time. We get through
>> rtc_timer_enqueue() and down to __rtc_set_alarm(). We loose the race
>> condition (I can do it, I've got really slow connection to DS3231) and
>> we return -ETIME from __rtc_set_alarm()
>>
>> if (scheduled <= now)
>> return -ETIME;
>>
>> and 0 from rtc_timer_enqueue() and the very same zero from
>> rtc_update_irq_enable(). The caller of ioctl() thinks they can expect
>> interrupts when, in fact, they won't receive any.
>>
>> The really weird stuff happens in rtc_timer_do_work(). For the timer to
>> be dequeued __rtc_set_alarm() needs to return EINVAL three times in a
>> row. In my setup this doesn't happen and the code keeps running loops
>> around "reporogram" and "again" labels.
>>
>> With my patch we never risk the above race condition between
>> __rtc_read_time() in rtc_update_irq_enable() and the one in
>> __rtc_set_alarm(), because we know rtc doesn't support alarms before we
>> start the race. In fact there is another race between __rtc_read_time()
>> and actually setting the alarm in the chip.
>>
>> IMHO the solution is to introduce RTC_HAS_ALARM flag for struct
>> rtc_device and check it at the very beginning of __rtc_set_alarm() the
>> same way it is being done in ds1337_set_alarm(). What are your thoughts?
>>
>
> I did introduce RTC_FEATURE_ALARM for that in v5.12. I'm sending patches
> that are not well tested but should solve your issue.
Oh, I didn't see that one coming (-; I was working on a slightly larger
feature elsewhere in the tree and didn't rebase too often. I will test
the patches.
--
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics
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prev parent reply other threads:[~2021-03-30 6:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20210308083541eucas1p1a8f772f12006ee6082b900c1a82aa298@eucas1p1.samsung.com>
2021-03-08 8:35 ` [PATCH] rtc: ds1307: set uie_unsupported if no interrupt is available Łukasz Stelmach
[not found] ` <CGME20210316121218eucas1p1f74d6e6cec7fc897051902a7da478fd0@eucas1p1.samsung.com>
2021-03-16 12:12 ` Lukasz Stelmach
2021-03-16 12:32 ` Alexandre Belloni
[not found] ` <CGME20210316180430eucas1p1a3cb26f40772b0af75782ff84908d731@eucas1p1.samsung.com>
2021-03-16 18:04 ` Lukasz Stelmach
[not found] ` <CGME20210317081944eucas1p123bd27f3203c937d2969a66fb06d6d9e@eucas1p1.samsung.com>
2021-03-17 8:19 ` [PATCH 1/2] WIP: Introduce has_alarm method for rtc devices Łukasz Stelmach
[not found] ` <CGME20210317081947eucas1p15a31b346977fba94bf154716c3d89cb0@eucas1p1.samsung.com>
2021-03-17 8:19 ` [PATCH 2/2] WIP: Provide has_alarm method Łukasz Stelmach
2021-03-30 0:02 ` [PATCH] rtc: ds1307: set uie_unsupported if no interrupt is available Alexandre Belloni
2021-03-30 0:03 ` [PATCH 1/3] rtc: ds1307: replace HAS_ALARM by RTC_FEATURE_ALARM Alexandre Belloni
2021-03-30 0:03 ` [PATCH 2/3] rtc: ds1307: remove flags Alexandre Belloni
[not found] ` <CGME20210402102743eucas1p23690e0df642a10fa0326a84fac6c0ed3@eucas1p2.samsung.com>
2021-04-02 10:27 ` Łukasz Stelmach
2021-03-30 0:03 ` [PATCH 3/3] rtc: rtc_update_irq_enable: rework UIE emulation Alexandre Belloni
[not found] ` <CGME20210402102813eucas1p1bae7ec57559fa8df622118275bf6fae0@eucas1p1.samsung.com>
2021-04-02 10:28 ` Łukasz Stelmach
[not found] ` <CGME20210402102655eucas1p24ee7e879816089921bf9752c3c483122@eucas1p2.samsung.com>
2021-04-02 10:26 ` [PATCH 1/3] rtc: ds1307: replace HAS_ALARM by RTC_FEATURE_ALARM Łukasz Stelmach
[not found] ` <CGME20210330065217eucas1p2c50a100bf0101e72dd753f37257f6a57@eucas1p2.samsung.com>
2021-03-30 6:52 ` Lukasz Stelmach [this message]
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