From: Jean Delvare <jdelvare@suse.de>
To: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Wolfram Sang <wsa@the-dreams.de>,
Jonathan Corbet <corbet@lwn.net>, Corey Minyard <minyard@acm.org>,
Guenter Roeck <linux@roeck-us.net>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Andrew Duggan <aduggan@synaptics.com>,
Christopher Heiny <cheiny@synaptics.com>,
linux-i2c@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-input@vger.kernel.org
Subject: Re: [PATCH v8 2/4] i2c-smbus: add SMBus Host Notify support
Date: Mon, 18 Jul 2016 16:31:09 +0200 [thread overview]
Message-ID: <20160718163109.4d2190e9@endymion> (raw)
In-Reply-To: <1465484030-28838-3-git-send-email-benjamin.tissoires@redhat.com>
Hi Benjamin, Wolfram,
Now that I have reviewed the i2c-i801 part of the implementation, I'm
wondering...
On Thu, 9 Jun 2016 16:53:48 +0200, Benjamin Tissoires wrote:
> +/**
> + * i2c_setup_smbus_host_notify - Allocate a new smbus_host_notify for the given
> + * I2C adapter.
> + * @adapter: the adapter we want to associate a Host Notify function
> + *
> + * Returns a struct smbus_host_notify pointer on success, and NULL on failure.
> + * The resulting smbus_host_notify must not be freed afterwards, it is a
> + * managed resource already.
> + */
> +struct smbus_host_notify *i2c_setup_smbus_host_notify(struct i2c_adapter *adap)
> +{
> + struct smbus_host_notify *host_notify;
> +
> + host_notify = devm_kzalloc(&adap->dev, sizeof(struct smbus_host_notify),
> + GFP_KERNEL);
> + if (!host_notify)
> + return NULL;
> +
> + host_notify->adapter = adap;
> +
> + spin_lock_init(&host_notify->lock);
> + INIT_WORK(&host_notify->work, smbus_host_notify_work);
Here we initialize a workqueue.
> +
> + return host_notify;
> +}
> +EXPORT_SYMBOL_GPL(i2c_setup_smbus_host_notify);
> +
> +/**
> + * i2c_handle_smbus_host_notify - Forward a Host Notify event to the correct
> + * I2C client.
> + * @host_notify: the struct host_notify attached to the relevant adapter
> + * @data: the Host Notify data which contains the payload and address of the
> + * client
> + * Context: can't sleep
> + *
> + * Helper function to be called from an I2C bus driver's interrupt
> + * handler. It will schedule the Host Notify work, in turn calling the
> + * corresponding I2C device driver's alert function.
> + *
> + * host_notify should be a valid pointer previously returned by
> + * i2c_setup_smbus_host_notify().
> + */
> +int i2c_handle_smbus_host_notify(struct smbus_host_notify *host_notify,
> + unsigned short addr, unsigned int data)
> +{
> + unsigned long flags;
> + struct i2c_adapter *adapter;
> +
> + if (!host_notify || !host_notify->adapter)
> + return -EINVAL;
> +
> + adapter = host_notify->adapter;
> +
> + spin_lock_irqsave(&host_notify->lock, flags);
> +
> + if (host_notify->pending) {
> + spin_unlock_irqrestore(&host_notify->lock, flags);
> + dev_warn(&adapter->dev, "Host Notify already scheduled.\n");
> + return -EBUSY;
> + }
> +
> + host_notify->payload = data;
> + host_notify->addr = addr;
> +
> + /* Mark that there is a pending notification and release the lock */
> + host_notify->pending = true;
> + spin_unlock_irqrestore(&host_notify->lock, flags);
> +
> + return schedule_work(&host_notify->work);
And here we use it.
> +}
> +EXPORT_SYMBOL_GPL(i2c_handle_smbus_host_notify);
But what happens on i2c_adapter removal? What prevents the following
sequence from happening?
1* A Host Notify event happens.
2* The event is handled and queued by i2c_handle_smbus_host_notify().
3* Someone tears down the underlying i2c_adapter (for example "rmmod
i2c-i801".)
4* The workqueue is processed, accessing memory which has already been
freed.
Of course it would be back luck, but that's pretty much the definition
of a race condition ;-)
To be on the safe side, don't we need a teardown function in i2c-smbus,
that could be called before i2c_del_adapter, which would remove the
host notify handle and flush the workqueue?
--
Jean Delvare
SUSE L3 Support
next prev parent reply other threads:[~2016-07-18 14:31 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-09 14:53 [PATCH v8 0/4] i2c-smbus: add support for HOST NOTIFY Benjamin Tissoires
2016-06-09 14:53 ` [PATCH v8 1/4] i2c: add a protocol parameter to the alert callback Benjamin Tissoires
2016-06-17 11:26 ` Wolfram Sang
2016-06-09 14:53 ` [PATCH v8 2/4] i2c-smbus: add SMBus Host Notify support Benjamin Tissoires
2016-06-17 11:26 ` Wolfram Sang
2016-07-18 9:37 ` Jean Delvare
2016-07-18 15:59 ` Benjamin Tissoires
2016-07-18 16:47 ` Jean Delvare
2016-07-18 14:31 ` Jean Delvare [this message]
2016-07-18 16:35 ` Benjamin Tissoires
2016-07-18 20:47 ` Jean Delvare
2016-06-09 14:53 ` [PATCH v8 3/4] i2c: i801: add support of Host Notify Benjamin Tissoires
2016-06-15 8:12 ` Benjamin Tissoires
2016-06-16 6:09 ` Wolfram Sang
2016-06-16 12:55 ` Benjamin Tissoires
2016-06-16 14:31 ` Wolfram Sang
2016-06-23 20:55 ` Dmitry Torokhov
2016-06-23 21:46 ` Wolfram Sang
2016-06-23 22:57 ` Dmitry Torokhov
2016-06-09 14:53 ` [PATCH v8 4/4] Input: synaptics-rmi4 - add SMBus support Benjamin Tissoires
2016-06-23 23:06 ` Dmitry Torokhov
2016-06-24 7:19 ` Benjamin Tissoires
2016-06-24 23:35 ` Dmitry Torokhov
2016-06-27 15:03 ` Benjamin Tissoires
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