Re: [PATCH v2 5/5] firmware: add DECLARE_FW_CUSTOM_FALLBACK() annotation

["Luis R. Rodriguez" <mcgrof@kernel.org>]

On Mon, Dec 19, 2016 at 11:23:17AM +0100, Julia Lawall wrote:
> 
> 
> On Fri, 16 Dec 2016, Luis R. Rodriguez wrote:
> 
> > We need to ensure that when driver developers use the custom firmware
> > fallback mechanism it was not a copy and paste bug. These use cases on
> > upstream drivers are rare, we only have 2 upstream users and its for
> > really old drivers. Since valid uses are rare but possible enable a
> > white-list for its use, and use this same white-list annotation to refer
> > to the documentation covering the custom use case.
> >
> > New faulty users can be reported via 0-day now.
> >
> > Cc: Fengguang Wu <fengguang.wu@intel.com>
> > Cc: Richard Purdie <rpurdie@rpsys.net>
> > Cc: Jacek Anaszewski <j.anaszewski@samsung.com>
> > Cc: linux-leds@vger.kernel.org
> > Cc: Abhay Salunke <Abhay_Salunke@dell.com>
> > Acked-by: Jacek Anaszewski <j.anaszewski@samsung.com>
> > Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
> > ---
> >  Documentation/driver-api/firmware/fallback-mechanisms.rst     | 7 +++++--
> >  drivers/firmware/dell_rbu.c                                   | 1 +
> >  drivers/leds/leds-lp55xx-common.c                             | 1 +
> >  include/linux/firmware.h                                      | 7 +++++++
> >  scripts/coccinelle/api/request_firmware-custom-fallback.cocci | 9 ++++++++-
> >  5 files changed, 22 insertions(+), 3 deletions(-)
> >
> > diff --git a/Documentation/driver-api/firmware/fallback-mechanisms.rst b/Documentation/driver-api/firmware/fallback-mechanisms.rst
> > index b87a292153c6..73f509a8d2de 100644
> > --- a/Documentation/driver-api/firmware/fallback-mechanisms.rst
> > +++ b/Documentation/driver-api/firmware/fallback-mechanisms.rst
> > @@ -184,8 +184,11 @@ load firmware for you through a custom path.
> >
> >  The custom fallback mechanism can often be enabled by mistake. We currently
> >  have only 2 users of it, and little justification to enable it for other users.
> > -Since it is a common driver developer mistake to enable it, help police for
> > -new users of the custom fallback mechanism with::
> > +Since it is a common driver developer mistake to enable it, driver developers
> > +should use DECLARE_FW_CUSTOM_FALLBACK() to both white-list and validate their
> > +use and also refer to the documentation for the custom loading solution.
> > +
> > +Invalid users of the custom fallback mechanism can be policed using::
> >
> >          $ export COCCI=scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
> >          $ make coccicheck MODE=report
> > diff --git a/drivers/firmware/dell_rbu.c b/drivers/firmware/dell_rbu.c
> > index 2f452f1f7c8a..3f2aa35bc54d 100644
> > --- a/drivers/firmware/dell_rbu.c
> > +++ b/drivers/firmware/dell_rbu.c
> > @@ -586,6 +586,7 @@ static ssize_t read_rbu_image_type(struct file *filp, struct kobject *kobj,
> >  	return size;
> >  }
> >
> > +DECLARE_FW_CUSTOM_FALLBACK("Documentation/dell_rbu.txt");
> >  static ssize_t write_rbu_image_type(struct file *filp, struct kobject *kobj,
> >  				    struct bin_attribute *bin_attr,
> >  				    char *buffer, loff_t pos, size_t count)
> > diff --git a/drivers/leds/leds-lp55xx-common.c b/drivers/leds/leds-lp55xx-common.c
> > index 5377f22ff994..04161428ee3b 100644
> > --- a/drivers/leds/leds-lp55xx-common.c
> > +++ b/drivers/leds/leds-lp55xx-common.c
> > @@ -219,6 +219,7 @@ static void lp55xx_firmware_loaded(const struct firmware *fw, void *context)
> >  	release_firmware(chip->fw);
> >  }
> >
> > +DECLARE_FW_CUSTOM_FALLBACK("Documentation/leds/leds-lp55xx.txt");
> >  static int lp55xx_request_firmware(struct lp55xx_chip *chip)
> >  {
> >  	const char *name = chip->cl->name;
> > diff --git a/include/linux/firmware.h b/include/linux/firmware.h
> > index b1f9f0ccb8ac..e6ca19c03dcc 100644
> > --- a/include/linux/firmware.h
> > +++ b/include/linux/firmware.h
> > @@ -8,6 +8,13 @@
> >  #define FW_ACTION_NOHOTPLUG 0
> >  #define FW_ACTION_HOTPLUG 1
> >
> > +/*
> > + * Helper for scripts/coccinelle/api/request_firmware-custom-fallback.cocci
> > + * and so users can also easily search for the documentation for the
> > + * respectively needed custom fallback mechanism.
> > + */
> > +#define DECLARE_FW_CUSTOM_FALLBACK(__usermode_helper)
> > +
> >  struct firmware {
> >  	size_t size;
> >  	const u8 *data;
> > diff --git a/scripts/coccinelle/api/request_firmware-custom-fallback.cocci b/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
> > index c7598cfc4780..68cacab35b76 100644
> > --- a/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
> > +++ b/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
> > @@ -17,6 +17,13 @@
> >  virtual report
> >  virtual context
> >
> > +@ r0 depends on report || context @
> > +declarer name DECLARE_FW_CUSTOM_FALLBACK;
> > +expression E;
> > +@@
> > +
> > +DECLARE_FW_CUSTOM_FALLBACK(E);
> > +
> >  @ r1 depends on report || context @
> >  expression mod, name, dev, gfp, drv, cb;
> >  position p;
> > @@ -30,7 +37,7 @@ position p;
> >  *request_firmware_nowait@p(mod, FW_ACTION_NOHOTPLUG, name, dev, gfp, drv, cb)
> 
> It looks suspicious that your added a new rule r0, that the python rule
> below depends on r0 failing, and that the rule with the * (context mode)
> does not depend on r0 in any way.

You're right, the context mode would report all cases, I've changed it as follows:

diff --git a/scripts/coccinelle/api/request_firmware-custom-fallback.cocci b/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
index 68cacab35b76..9548e5be9c0e 100644
--- a/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
+++ b/scripts/coccinelle/api/request_firmware-custom-fallback.cocci
@@ -24,7 +24,7 @@ expression E;
 
 DECLARE_FW_CUSTOM_FALLBACK(E);
 
-@ r1 depends on report || context @
+@ r1 depends on !r0 && report || context @
 expression mod, name, dev, gfp, drv, cb;
 position p;
 @@
@@ -37,7 +37,7 @@ position p;
 *request_firmware_nowait@p(mod, FW_ACTION_NOHOTPLUG, name, dev, gfp, drv, cb)
 )
 
-@script:python depends on report && !r0 @
+@script:python depends on report && r1 @
 p << r1.p;
 @@