From: Lino Sanfilippo <LinoSanfilippo@gmx.de>
To: Jarkko Sakkinen <jarkko@kernel.org>, Lukas Wunner <lukas@wunner.de>
Cc: peterhuewe@gmx.de, jgg@ziepe.ca, stefanb@linux.vnet.ibm.com,
linux@mniewoehner.de, linux-integrity@vger.kernel.org,
linux-kernel@vger.kernel.org, jandryuk@gmail.com,
pmenzel@molgen.mpg.de, l.sanfilippo@kunbus.com,
p.rosenberger@kunbus.com
Subject: Re: [PATCH v8 08/11] tpm, tpm: Implement usage counter for locality
Date: Tue, 25 Oct 2022 02:25:39 +0200 [thread overview]
Message-ID: <0094438d-cf8e-da81-c969-119f90baf3db@gmx.de> (raw)
In-Reply-To: <Y1TQiIw0m+8BSzMs@kernel.org>
On 23.10.22 07:26, Jarkko Sakkinen wrote:
> On Tue, Oct 18, 2022 at 08:25:08AM +0200, Lukas Wunner wrote:
>> On Tue, Oct 18, 2022 at 01:57:29AM +0200, Lino Sanfilippo wrote:
>>> Implement a usage counter for the (default) locality used by the TPM TIS
>>> driver:
>>> Request the locality from the TPM if it has not been claimed yet, otherwise
>>> only increment the counter. Also release the locality if the counter is 0
>>> otherwise only decrement the counter. Ensure thread-safety by protecting
>>> the counter with a mutex.
>>>
>>> This allows to request and release the locality from a thread and the
>>> interrupt handler at the same time without the danger to interfere with
>>> each other.
>> [...]
>>> +static int tpm_tis_release_locality(struct tpm_chip *chip, int l)
>>> {
>>> struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>>>
>>> - tpm_tis_write8(priv, TPM_ACCESS(l), TPM_ACCESS_ACTIVE_LOCALITY);
>>> + mutex_lock(&priv->locality_count_mutex);
>>> + priv->locality_count--;
>>> + if (priv->locality_count == 0)
>>> + tpm_tis_release_locality_locked(priv, l);
>>> + mutex_unlock(&priv->locality_count_mutex);
>>>
>>> return 0;
>>> }
>>
>> Hm, any reason not to use struct kref for the locality counter?
>> Provides correct memory ordering (no mutex needed) and allows for
>> calling a release function too upon reaching 0.
>
> I proposed for last version kref. I have no idea why this is still
> using mutex. And now I apparently have proposed rcu for the whole
> struct (forgot what I had put my feedback for earlier version).
>
> This keeps being confusing patch as the commit message does not
> really go to the bottom line why mutex is really the best possible
> choice here.
>
I actually tried to implement this via kref but then came to the
conclusion it is rather not a good choice for our case. Please
see my response to your former request to implement this via kref:
https://lore.kernel.org/all/09eefdab-f677-864a-99f7-869d7a8744c2@gmx.de/
Regards,
Lino
next prev parent reply other threads:[~2022-10-25 1:13 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-17 23:57 [PATCH v8 00/11] TPM IRQ fixes Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 01/11] tpm, tpm_tis: Avoid cache incoherency in test for interrupts Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 02/11] tpm, tpm_tis: Claim locality before writing TPM_INT_ENABLE register Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 03/11] tpm, tpm_tis: Disable interrupts if tpm_tis_probe_irq() failed Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 04/11] tpm, tmp_tis: Claim locality before writing interrupt registers Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 05/11] tpm, tpm_tis: Only handle supported interrupts Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 06/11] tpm, tpm_tis: Move interrupt mask checks into own function Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 07/11] tpm, tpm_tis: do not check for the active locality in interrupt handler Lino Sanfilippo
2022-10-23 4:32 ` Jarkko Sakkinen
2022-10-17 23:57 ` [PATCH v8 08/11] tpm, tpm: Implement usage counter for locality Lino Sanfilippo
2022-10-18 6:25 ` Lukas Wunner
2022-10-18 7:42 ` Lino Sanfilippo
2022-10-23 5:26 ` Jarkko Sakkinen
2022-10-25 0:25 ` Lino Sanfilippo [this message]
2022-11-01 1:06 ` Jarkko Sakkinen
2022-10-23 4:40 ` Jarkko Sakkinen
2022-10-25 0:15 ` Lino Sanfilippo
2022-11-01 1:06 ` Jarkko Sakkinen
2022-11-04 16:18 ` Lino Sanfilippo
2022-11-07 16:03 ` Jarkko Sakkinen
2022-10-17 23:57 ` [PATCH v8 09/11] tpm, tpm_tis: Request threaded interrupt handler Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 10/11] tpm, tpm_tis: Claim locality in " Lino Sanfilippo
2022-10-17 23:57 ` [PATCH v8 11/11] tpm, tpm_tis: Enable interrupt test Lino Sanfilippo
2022-10-23 4:33 ` Jarkko Sakkinen
2022-10-23 4:34 ` Jarkko Sakkinen
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