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Subject: Re: [PATCH] Revert "seqlock: lockdep assert non-preemptibility on
 seqcount_t write"
To:     =?UTF-8?Q?Valdis_Kl=c4=93tnieks?= <valdis.kletnieks@vt.edu>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Mark Starovoytov <mstarovoitov@marvell.com>,
        Igor Russkikh <irusskikh@marvell.com>,
        "David S. Miller" <davem@davemloft.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        "Ahmed S. Darwish" <a.darwish@linutronix.de>,
        linux-kernel@vger.kernel.org, mingo@redhat.com, paulmck@kernel.org,
        peterz@infradead.org, rostedt@goodmis.org, tglx@linutronix.de,
        will@kernel.org
References: <20200810085954.GA1591892@kroah.com>
 <20200810095428.2602276-1-a.darwish@linutronix.de>
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From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <a873e584-ddf3-dacd-4901-514bd961841e@roeck-us.net>
Date:   Wed, 19 Aug 2020 09:15:14 -0700
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On 8/19/20 12:34 AM, Valdis Kl=C4=93tnieks wrote:
> On Wed, 19 Aug 2020 09:00:22 +0200, Sebastian Andrzej Siewior said:
>> On 2020-08-18 17:56:49 [-0700], Guenter Roeck wrote:
>>> Nice catch. FWIW, there is no obvious reason why this would need to b=
e atomic.
>>> The calling code does not set a lock, meaning there can be two (or mo=
re)
>>> callers entering this code. Weird, especially since the code looks li=
ke it
>>> would actually need a mutex to work correctly. It might be interestin=
g to
>>> see what happens if there are, say, half a dozen scripts/processes tr=
ying
>>> to read the hwmon attribute introduced by this patch at the same time=
=2E
>>
>> =3D> https://lkml.kernel.org/r/20200818161439.3dkf6jzp3vuwmvvh@linutro=
nix.de
>=20
> Looks reasonable to me, though I've not verified that it's preemptible =
at that
> point...
>=20

hw_atl_b0_get_mac_temp is called through the .hw_get_mac_temp callback.
This callback is executed from aq_hwmon_read(), which in turn is called
from the hwmon core, more specifically from hwmon_attr_show().
Calls from the hwmon core are unlocked.

Guenter


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