linux-kernel - Re: Re: [PATCH net v4] nfc: nfcmrvl: main: reorder destructive operations in nfcmrvl_nci_unregister

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Date:   Thu, 28 Apr 2022 12:03:45 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Jakub Kicinski" <kuba@...nel.org>
Cc:     krzysztof.kozlowski@...aro.org, pabeni@...hat.com,
        linux-kernel@...r.kernel.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, alexander.deucher@....com,
        akpm@...ux-foundation.org, broonie@...nel.org,
        netdev@...r.kernel.org, linma@....edu.cn
Subject: Re: Re: [PATCH net v4] nfc: nfcmrvl: main: reorder destructive
 operations in nfcmrvl_nci_unregister_dev to avoid bugs

Hello,

On Wed, 27 Apr 2022 17:45:48 -0700 Jakub Kicinski wrote:

> > diff --git a/net/nfc/core.c b/net/nfc/core.c
> > index dc7a2404efd..1d91334ee86 100644
> > --- a/net/nfc/core.c
> > +++ b/net/nfc/core.c
> > @@ -25,6 +25,8 @@
> >  #define NFC_CHECK_PRES_FREQ_MS	2000
> >  
> >  int nfc_devlist_generation;
> > +/* nfc_download: used to judge whether nfc firmware download could start */
> > +static bool nfc_download;
> >  DEFINE_MUTEX(nfc_devlist_mutex);
> >  
> >  /* NFC device ID bitmap */
> > @@ -38,7 +40,7 @@ int nfc_fw_download(struct nfc_dev *dev, const char *firmware_name)
> >  
> >  	device_lock(&dev->dev);
> >  
> > -	if (!device_is_registered(&dev->dev)) {
> > +	if (!device_is_registered(&dev->dev) || !nfc_download) {
> >  		rc = -ENODEV;
> >  		goto error;
> >  	}
> > @@ -1134,6 +1136,7 @@ int nfc_register_device(struct nfc_dev *dev)
> >  			dev->rfkill = NULL;
> >  		}
> >  	}
> > +	nfc_download = true;
> >  	device_unlock(&dev->dev);
> >  
> >  	rc = nfc_genl_device_added(dev);
> > @@ -1166,6 +1169,7 @@ void nfc_unregister_device(struct nfc_dev *dev)
> >  		rfkill_unregister(dev->rfkill);
> >  		rfkill_destroy(dev->rfkill);
> >  	}
> > +	nfc_download = false;
> >  	device_unlock(&dev->dev);
> >  
> >  	if (dev->ops->check_presence) {
> 
> You can't use a single global variable, there can be many devices 
> each with their own lock.
> 
> Paolo suggested adding a lock, if spin lock doesn't fit the bill
> why not add a mutex?

We could not use mutex either, because the release_firmware() is also called by fw_dnld_timeout()
which is a timer handler. If we use mutex lock in a timer handler, it will cause sleep in atomic bug.
The process is shown below:

nfcmrvl_fw_dnld_start
 ...              
 mod_timer 
 (wait a time)  
 fw_dnld_timeout
   fw_dnld_over 
    release_firmware       

I will change the single global variable to dev->dev_up flag, which is shown below:

diff --git a/drivers/nfc/nfcmrvl/main.c b/drivers/nfc/nfcmrvl/main.c
index 2fcf545012b..1a5284de434 100644
--- a/drivers/nfc/nfcmrvl/main.c
+++ b/drivers/nfc/nfcmrvl/main.c
@@ -183,6 +183,7 @@ void nfcmrvl_nci_unregister_dev(struct nfcmrvl_private *priv)
 {
        struct nci_dev *ndev = priv->ndev;

+       nci_unregister_device(ndev);
        if (priv->ndev->nfc_dev->fw_download_in_progress)
                nfcmrvl_fw_dnld_abort(priv);

@@ -191,7 +192,6 @@ void nfcmrvl_nci_unregister_dev(struct nfcmrvl_private *priv)
        if (gpio_is_valid(priv->config.reset_n_io))
                gpio_free(priv->config.reset_n_io);

-       nci_unregister_device(ndev);
        nci_free_device(ndev);
        kfree(priv);
 }
diff --git a/net/nfc/core.c b/net/nfc/core.c
index dc7a2404efd..09f54c599fe 100644
--- a/net/nfc/core.c
+++ b/net/nfc/core.c
@@ -1166,6 +1166,7 @@ void nfc_unregister_device(struct nfc_dev *dev)
                rfkill_unregister(dev->rfkill);
                rfkill_destroy(dev->rfkill);
        }
+       dev->dev_up = false;
        device_unlock(&dev->dev);

        if (dev->ops->check_presence) {

The above solution has been tested, it is well synchronized.

Best regards,
Duoming Zhou