From: Alexandre Belloni <alexandre.belloni@bootlin.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: William Breathitt Gray <vilhelm.gray@gmail.com>,
jic23@kernel.org, linux-stm32@st-md-mailman.stormreply.com,
kernel@pengutronix.de, a.fatoum@pengutronix.de,
kamel.bouhara@bootlin.com, gwendal@chromium.org,
david@lechnology.com, linux-iio@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, syednwaris@gmail.com,
patrick.havelange@essensium.com, fabrice.gasnier@st.com,
mcoquelin.stm32@gmail.com, alexandre.torgue@st.com,
o.rempel@pengutronix.de, jarkko.nikula@linux.intel.com,
Dan Carpenter <dan.carpenter@oracle.com>
Subject: Re: [PATCH v17 2/9] counter: Add character device interface
Date: Sun, 17 Oct 2021 16:02:42 +0200 [thread overview]
Message-ID: <YWwtAm0o6wVMG6xc@piout.net> (raw)
In-Reply-To: <YWwqE5T6h5j14M/M@kroah.com>
On 17/10/2021 15:50:11+0200, Greg KH wrote:
> Note, review of this now that it has been submitted in a pull request to
> me, sorry I missed this previously...
>
> On Wed, Sep 29, 2021 at 12:15:59PM +0900, William Breathitt Gray wrote:
> > +static int counter_chrdev_open(struct inode *inode, struct file *filp)
> > +{
> > + struct counter_device *const counter = container_of(inode->i_cdev,
> > + typeof(*counter),
> > + chrdev);
> > +
> > + /* Ensure chrdev is not opened more than 1 at a time */
> > + if (!atomic_add_unless(&counter->chrdev_lock, 1, 1))
> > + return -EBUSY;
>
> I understand the feeling that you wish to stop userspace from doing
> this, but really, it does not work. Eventhough you are doing this
> correctly (you should see all the other attempts at doing this), you are
> not preventing userspace from having multiple processes access this
> device node at the same time, so please, don't even attempt to stop this
> from happening.
>
> So you can drop the atomic "lock" you have here, it's not needed at all.
>
Could you elaborate a bit here because we've had a similar thing in the
RTC subsystem:
https://elixir.bootlin.com/linux/latest/source/drivers/rtc/dev.c#L28
And it would mean I can remove rtc->flags completely.
--
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
next prev parent reply other threads:[~2021-10-17 14:02 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 3:15 [PATCH v17 0/9] Introduce the Counter character device interface William Breathitt Gray
2021-09-29 3:15 ` [PATCH v17 1/9] counter: Move counter enums to uapi header William Breathitt Gray
2021-09-29 3:15 ` [PATCH v17 2/9] counter: Add character device interface William Breathitt Gray
2021-10-17 13:50 ` Greg KH
2021-10-17 14:02 ` Alexandre Belloni [this message]
2021-10-17 14:40 ` Greg KH
2021-10-17 15:35 ` Alexandre Belloni
2021-09-29 3:16 ` [PATCH v17 3/9] docs: counter: Document " William Breathitt Gray
2021-09-29 3:16 ` [PATCH v17 4/9] tools/counter: Create Counter tools William Breathitt Gray
2021-09-29 3:16 ` [PATCH v17 5/9] counter: Implement signalZ_action_component_id sysfs attribute William Breathitt Gray
2021-10-17 13:51 ` Greg KH
2021-09-29 3:16 ` [PATCH v17 6/9] counter: Implement *_component_id sysfs attributes William Breathitt Gray
2021-09-29 3:16 ` [PATCH v17 7/9] counter: Implement events_queue_size sysfs attribute William Breathitt Gray
2021-09-29 3:16 ` [PATCH v17 8/9] counter: 104-quad-8: Replace mutex with spinlock William Breathitt Gray
2021-09-29 3:16 ` [PATCH v17 9/9] counter: 104-quad-8: Add IRQ support for the ACCES 104-QUAD-8 William Breathitt Gray
2021-09-30 17:21 ` [PATCH v17 0/9] Introduce the Counter character device interface Jonathan Cameron
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