linux-kernel - Re: [PATCH] devcoredump: Remove devcoredump device if failing device is gone

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Date: Fri, 19 Jan 2024 18:13:45 +0000
From: "Souza, Jose" <jose.souza@...el.com>
To: "Vivi, Rodrigo" <rodrigo.vivi@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
	"johannes@...solutions.net" <johannes@...solutions.net>
Subject: Re: [PATCH] devcoredump: Remove devcoredump device if failing device
 is gone

On Wed, 2024-01-17 at 14:53 -0500, Rodrigo Vivi wrote:
> Make dev_coredumpm a real device managed helper, that not only
> frees the device after a scheduled delay (DEVCD_TIMEOUT), but
> also when the failing/crashed device is gone.
> 
> The module remove for the drivers using devcoredump are currently
> broken if attempted between the crash and the DEVCD_TIMEOUT, since
> the symbolic sysfs link won't be deleted.
> 
> On top of that, for PCI devices, the unbind of the device will
> call the pci .remove void function, that cannot fail. At that
> time, our device is pretty much gone, but the read and free
> functions are alive trough the devcoredump device and they
> can get some NULL dereferences or use after free.
> 
> So, if the failing-device is gone, let's cancel the scheduled
> work and remove devcoredump-device immediately.
> 
> Cc: Jose Souza <jose.souza@...el.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Cc: Johannes Berg <johannes@...solutions.net>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@...el.com>
> ---
>  drivers/base/devcoredump.c | 29 ++++++++++++++++++++++-------
>  1 file changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c
> index 7e2d1f0d903a..6db7a2fd9a02 100644
> --- a/drivers/base/devcoredump.c
> +++ b/drivers/base/devcoredump.c
> @@ -8,6 +8,7 @@
>  #include <linux/module.h>
>  #include <linux/device.h>
>  #include <linux/devcoredump.h>
> +#include <linux/devm-helpers.h>
>  #include <linux/list.h>
>  #include <linux/slab.h>
>  #include <linux/fs.h>
> @@ -118,19 +119,24 @@ static ssize_t devcd_data_read(struct file *filp, struct kobject *kobj,
>  	return devcd->read(buffer, offset, count, devcd->data, devcd->datalen);
>  }
>  
> -static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
> -				struct bin_attribute *bin_attr,
> -				char *buffer, loff_t offset, size_t count)
> +static void devcd_remove_now(struct devcd_entry *devcd)

this function can also be used by devcd_free().

Other than that LGTM.

>  {
> -	struct device *dev = kobj_to_dev(kobj);
> -	struct devcd_entry *devcd = dev_to_devcd(dev);
> -
>  	mutex_lock(&devcd->mutex);
>  	if (!devcd->delete_work) {
>  		devcd->delete_work = true;
>  		mod_delayed_work(system_wq, &devcd->del_wk, 0);
>  	}
>  	mutex_unlock(&devcd->mutex);
> +}
> +
> +static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
> +				struct bin_attribute *bin_attr,
> +				char *buffer, loff_t offset, size_t count)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct devcd_entry *devcd = dev_to_devcd(dev);
> +
> +	devcd_remove_now(devcd);
>  
>  	return count;
>  }
> @@ -304,6 +310,12 @@ static ssize_t devcd_read_from_sgtable(char *buffer, loff_t offset,
>  				  offset);
>  }
>  
> +static void devcd_remove(void *data)
> +{
> +	struct devcd_entry *devcd = data;
> +	devcd_remove_now(devcd);
> +}
> +
>  /**
>   * dev_coredumpm - create device coredump with read/free methods
>   * @dev: the struct device for the crashed device
> @@ -379,7 +391,10 @@ void dev_coredumpm(struct device *dev, struct module *owner,
>  
>  	dev_set_uevent_suppress(&devcd->devcd_dev, false);
>  	kobject_uevent(&devcd->devcd_dev.kobj, KOBJ_ADD);
> -	INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
> +	if (devm_add_action(dev, devcd_remove, devcd))
> +		dev_warn(dev, "devcoredump managed auto-removal registration failed\n");
> +	if (devm_delayed_work_autocancel(dev, &devcd->del_wk, devcd_del))
> +		dev_warn(dev, "devcoredump managed autocancel work failed\n");
>  	schedule_delayed_work(&devcd->del_wk, DEVCD_TIMEOUT);
>  	mutex_unlock(&devcd->mutex);
>  	return;