Re: [PATCH v2 3/4] cxl/pci: Fix sanitize notifier setup

[Dave Jiang <dave.jiang@intel.com>]

On 9/29/23 16:09, Dan Williams wrote:
> Fix a race condition between the mailbox-background command interrupt
> firing and the security-state sysfs attribute being removed.
> 
> The race is difficult to see due to the awkward placement of the
> sanitize-notifier setup code and the multiple places the teardown calls
> are made, cxl_memdev_security_init() and cxl_memdev_security_shutdown().
> 
> Unify setup in one place, cxl_sanitize_setup_notifier(). Arrange for
> the paired cxl_sanitize_teardown_notifier() to safely quiet the notifier
> and let the cxl_memdev + irq be unregistered later in the flow.
> 
> This fix is also needed as a preparation fix for a memdev unregistration
> crash.
> 
> Reported-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> Cc: Dave Jiang <dave.jiang@intel.com>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Fixes: 0c36b6ad436a ("cxl/mbox: Add sanitization handling machinery")
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  drivers/cxl/core/memdev.c |   42 ----------------------------------------
>  drivers/cxl/pci.c         |   47 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index 2a7a07f6d165..a950091e5640 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -556,20 +556,11 @@ void clear_exclusive_cxl_commands(struct cxl_memdev_state *mds,
>  }
>  EXPORT_SYMBOL_NS_GPL(clear_exclusive_cxl_commands, CXL);
>  
> -static void cxl_memdev_security_shutdown(struct device *dev)
> -{
> -	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
> -	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlmd->cxlds);
> -
> -	cancel_delayed_work_sync(&mds->security.poll_dwork);
> -}
> -
>  static void cxl_memdev_shutdown(struct device *dev)
>  {
>  	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
>  
>  	down_write(&cxl_memdev_rwsem);
> -	cxl_memdev_security_shutdown(dev);
>  	cxlmd->cxlds = NULL;
>  	up_write(&cxl_memdev_rwsem);
>  }
> @@ -1001,35 +992,6 @@ static const struct file_operations cxl_memdev_fops = {
>  	.llseek = noop_llseek,
>  };
>  
> -static void put_sanitize(void *data)
> -{
> -	struct cxl_memdev_state *mds = data;
> -
> -	sysfs_put(mds->security.sanitize_node);
> -}
> -
> -static int cxl_memdev_security_init(struct cxl_memdev *cxlmd)
> -{
> -	struct cxl_dev_state *cxlds = cxlmd->cxlds;
> -	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlds);
> -	struct device *dev = &cxlmd->dev;
> -	struct kernfs_node *sec;
> -
> -	sec = sysfs_get_dirent(dev->kobj.sd, "security");
> -	if (!sec) {
> -		dev_err(dev, "sysfs_get_dirent 'security' failed\n");
> -		return -ENODEV;
> -	}
> -	mds->security.sanitize_node = sysfs_get_dirent(sec, "state");
> -	sysfs_put(sec);
> -	if (!mds->security.sanitize_node) {
> -		dev_err(dev, "sysfs_get_dirent 'state' failed\n");
> -		return -ENODEV;
> -	}
> -
> -	return devm_add_action_or_reset(cxlds->dev, put_sanitize, mds);
> - }
> -
>  struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
>  {
>  	struct cxl_memdev *cxlmd;
> @@ -1058,10 +1020,6 @@ struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
>  	if (rc)
>  		goto err;
>  
> -	rc = cxl_memdev_security_init(cxlmd);
> -	if (rc)
> -		goto err;
> -
>  	rc = devm_add_action_or_reset(cxlds->dev, cxl_memdev_unregister, cxlmd);
>  	if (rc)
>  		return ERR_PTR(rc);
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index ac4e434b0806..b0023e479315 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -165,6 +165,49 @@ static void cxl_mbox_sanitize_work(struct work_struct *work)
>  	mutex_unlock(&mds->mbox_mutex);
>  }
>  
> +static void cxl_sanitize_teardown_notifier(void *data)
> +{
> +	struct cxl_memdev_state *mds = data;
> +	struct kernfs_node *state;
> +
> +	/*
> +	 * Prevent new irq triggered invocations of the workqueue and
> +	 * flush inflight invocations.
> +	 */
> +	mutex_lock(&mds->mbox_mutex);
> +	state = mds->security.sanitize_node;
> +	mds->security.sanitize_node = NULL;
> +	mutex_unlock(&mds->mbox_mutex);
> +
> +	cancel_delayed_work_sync(&mds->security.poll_dwork);
> +	sysfs_put(state);
> +}
> +
> +static int cxl_sanitize_setup_notifier(struct cxl_memdev *cxlmd)
> +{
> +	struct cxl_dev_state *cxlds = cxlmd->cxlds;
> +	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlds);
> +	struct device *dev = cxlds->dev;
> +	struct kernfs_node *sec;
> +
> +	if (!test_bit(CXL_SEC_ENABLED_SANITIZE, mds->security.enabled_cmds))
> +		return 0;
> +
> +	sec = sysfs_get_dirent(dev->kobj.sd, "security");
> +	if (!sec) {
> +		dev_err(dev, "sanitize notification setup failure\n");
> +		return -ENOENT;
> +	}
> +	mds->security.sanitize_node = sysfs_get_dirent(sec, "state");
> +	sysfs_put(sec);
> +	if (!mds->security.sanitize_node) {
> +		dev_err(dev, "sanitize notification setup failure\n");
> +		return -ENOENT;
> +	}
> +
> +	return devm_add_action_or_reset(dev, cxl_sanitize_teardown_notifier, mds);
> +}
> +
>  /**
>   * __cxl_pci_mbox_send_cmd() - Execute a mailbox command
>   * @mds: The memory device driver data
> @@ -875,6 +918,10 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	if (rc)
>  		return rc;
>  
> +	rc = cxl_sanitize_setup_notifier(cxlmd);
> +	if (rc)
> +		return rc;
> +
>  	pmu_count = cxl_count_regblock(pdev, CXL_REGLOC_RBI_PMU);
>  	for (i = 0; i < pmu_count; i++) {
>  		struct cxl_pmu_regs pmu_regs;
>