Re: [PATCH v2 2/5] firmware: annotate thou shalt not request fw on init or probe

[Daniel Vetter]

On Fri, Jun 17, 2016 at 12:54 AM, Luis R. Rodriguez <mcgrof@xxxxxxxxxx> wrote:
> Thou shalt not make firmware calls early on init or probe.
>
> systemd already ripped support out for the usermode helper
> a while ago, there are still users that require the usermode helper,
> however systemd's use of the usermode helper exacerbated a long
> lasting issue of the fact that we have many drivers that load
> firmware on init or probe. Independent of the usermode helper
> loading firmware on init or probe is a bad idea for a few reasons.
>
> When the firmware is read directly from the filesystem by the kernel,
> if the driver is built-in to the kernel the firmware may not yet be
> available, for such uses one could use initramfs and stuff the firmware
> inside, or one also use CONFIG_EXTRA_FIRMWARE; however not all distributions
> use this, as such generally one cannot count on this. There is another
> corner cases to consider, since we are accessing the firmware directly folks
> cannot expect new found firmware on a filesystem after we switch off from
> an initramfs with pivot_root().
>
> Supporting such situations is possible today but fixing it for good is
> really complex due to the large amount of variablity in the boot up
> process.
>
> Instead just document the expectations properly and add a grammar rule to
> enable folks to check / validate / police if drivers are using the request
> firmware API early on init or probe.
>
> The SmPL rule used to check for the probe routine is loose and is
> currently defined through a regexp, that can easily be extended to any
> other known bus probe routine names. It also uses the new Python
> iteration support which allows us to backtrack from a request_firmware*()
> call back to a possible probe or init, iteratively. Without iteration
> we would only be able to get reports for callers who directly use the
> request_firmware*() API on the initial probe or init routine.
>
> There are 4 offenders at this time:
>
> mcgrof@ergon ~/linux-next (git::20160609)$ export COCCI=scripts/coccinelle/api/request_firmware.cocci
> mcgrof@ergon ~/linux-next (git::20160609)$ make coccicheck MODE=report
>
> drivers/fmc/fmc-fakedev.c: ERROR: driver call request firmware call on its init routine on line 321.
> drivers/fmc/fmc-write-eeprom.c: ERROR: driver call request firmware call on its probe routine on line 136.
> drivers/tty/serial/rp2.c: ERROR: driver call request firmware call on its probe routine on line 796.
> drivers/tty/serial/ucc_uart.c: ERROR: driver call request firmware call on its probe routine on line 1246.

Plus all gpu drivers which need firmware. And yes we must load them at
probe because people are generally pissed when they boot their machine
and the screen goes black. On top of that a lot of people want their
gpu drivers to be built-in, but can't ship the firmware blobs in the
kernel image because gpl. Yep, there's a bit a contradiction there ...

I think what would work is loading the different subsystems of the
driver in parallel (we already do that largely), and then if one
firmware blob isn't there yet simply stall that async worker until it
shows up. But the answers I've gotten thus far from request_firmware()
folks (well at least Greg) is don't do that ...

Is that problem still somewhere on the radar? Atm there's various
wait_for_rootfs hacks out there floating in vendor/product trees.
"Avoid at all costs" sounds like upstream prefers to not care about
android/cros in those case (yes I know most arm socs don't need
firmware, which would make it a problem fo just be a subset of all
devices).
-Daniel

> I checked and verified all these are valid reports. This list also matches
> the same list as in 20150805, so we have fortunately not gotten worse.
> Let's keep it that way and also fix these drivers.
>
> v2: changes from v1 [0]:
>
> o This now supports iteration, this extends our coverage on the report
>
> o Update documentation and commit log to accept the fate of not being
>   able to remove the usermode helper.
>
> [0] https://lkml.kernel.org/r/1440811107-861-1-git-send-email-mcgrof@xxxxxxxxxxxxxxxx
>
> Cc: Alessandro Rubini <rubini@xxxxxxxxx>
> Cc: Kevin Cernekee <cernekee@xxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Julia Lawall <Julia.Lawall@xxxxxxx>
> Cc: Gilles Muller <Gilles.Muller@xxxxxxx>
> Cc: Nicolas Palix <nicolas.palix@xxxxxxx>
> Cc: Thierry Martinez <martinez@xxxxxxxx>
> Cc: Michal Marek <mmarek@xxxxxxxx>
> Cc: cocci@xxxxxxxxxxxxxxx
> Cc: Alessandro Rubini <rubini@xxxxxxxxx>
> Cc: Kevin Cernekee <cernekee@xxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Jiri Slaby <jslaby@xxxxxxxx>
> Cc: linux-serial@xxxxxxxxxxxxxxx
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-serial@xxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> ---
>  Documentation/firmware_class/README                |  20 ++++
>  drivers/base/Kconfig                               |   2 +-
>  .../request_firmware-avoid-init-probe-init.cocci   | 130 +++++++++++++++++++++
>  3 files changed, 151 insertions(+), 1 deletion(-)
>  create mode 100644 scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
>
> diff --git a/Documentation/firmware_class/README b/Documentation/firmware_class/README
> index cafdca8b3b15..056d1cb9d365 100644
> --- a/Documentation/firmware_class/README
> +++ b/Documentation/firmware_class/README
> @@ -93,6 +93,26 @@
>     user contexts to request firmware asynchronously, but can't be called
>     in atomic contexts.
>
> +Requirements:
> +=============
> +
> +You should avoid at all costs requesting firmware on both init and probe paths
> +of your device driver. Reason for this is the complexity needed to ensure a
> +firmware will be available for a driver early in boot through different
> +build configurations. Consider built-in drivers needing firmware early, or
> +consider a driver assuming it will only get firmware after pivot_root().
> +
> +Drivers that really need firmware early should use stuff the firmware in
> +initramfs or consider using CONFIG_EXTRA_FIRMWARE. Using initramfs is much
> +more portable to more distributions as not all distributions wish to enable
> +CONFIG_EXTRA_FIRMWARE. Should a driver require the firmware being built-in
> +it should depend on CONFIG_EXTRA_FIRMWARE. There is no current annotation for
> +requiring a firmware on initramfs.
> +
> +If you're a maintainer you can help police this with:
> +
> +$ export COCCI=scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
> +$ make coccicheck MODE=report
>
>   about in-kernel persistence:
>   ---------------------------
> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> index 98504ec99c7d..12b4f5551501 100644
> --- a/drivers/base/Kconfig
> +++ b/drivers/base/Kconfig
> @@ -152,7 +152,7 @@ config FW_LOADER_USER_HELPER
>         bool
>
>  config FW_LOADER_USER_HELPER_FALLBACK
> -       bool "Fallback user-helper invocation for firmware loading"
> +       bool "Fallback user-helper invocation for firmware loading (avoid)"
>         depends on FW_LOADER
>         select FW_LOADER_USER_HELPER
>         help
> diff --git a/scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci b/scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
> new file mode 100644
> index 000000000000..cf180c59e042
> --- /dev/null
> +++ b/scripts/coccinelle/api/request_firmware-avoid-init-probe-init.cocci
> @@ -0,0 +1,130 @@
> +///
> +/// Thou shalt not request firmware on init or probe
> +///
> +// Confidence: High
> +// Copyright: (C) 2016 Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
> +// Copyright: (C) 2015 Julia Lawall, Inria/LIP6.
> +//
> +// GPLv2.
> +// URL: http://coccinelle.lip6.fr/
> +// Options: --no-includes --include-headers --no-show-diff
> +// Requires: 1.0.5
> +//
> +// Coccinelle 1.0.5 is required given that this uses the shiny new
> +// python iteration feature.
> +
> +virtual report
> +virtual after_start
> +
> +// -------------------------------------------------------------------------
> +
> +@initialize:python@
> +@@
> +
> +seen = set()
> +
> +def add_if_not_present(f, file, starter_var):
> +    if (f, file, starter_var) not in seen:
> +        seen.add((f, file, starter_var))
> +        it = Iteration()
> +        if file != None:
> +            it.set_files([file])
> +    it.add_virtual_rule(after_start)
> +    it.add_virtual_rule(report)
> +    it.add_virtual_identifier(fn, f)
> +    it.add_virtual_identifier(starter, starter_var)
> +    it.register()
> +
> +reported = set()
> +
> +def print_err(str, file, line):
> +    if (file, line) not in reported:
> +        reported.add((file, line))
> +       print "%s: ERROR: driver call request firmware call on its %s routine on line %d." % (file, str, line)
> +
> +@ defines_module_init@
> +declarer name module_init;
> +identifier init;
> +@@
> +
> +module_init(init);
> +
> +@ has_probe depends on defines_module_init@
> +identifier drv_calls, drv_probe;
> +type bus_driver;
> +identifier probe_op =~ "(probe)";
> +@@
> +
> +bus_driver drv_calls = {
> +       .probe_op = drv_probe,
> +};
> +
> +@hascall depends on !after_start && defines_module_init@
> +position p;
> +@@
> +
> +(
> +request_firmware@p(...)
> +|
> +request_firmware_nowait@p(...)
> +|
> +request_firmware_direct@p(...)
> +)
> +
> +@script:python@
> +init << defines_module_init.init;
> +p << hascall.p;
> +@@
> +
> +if p[0].current_element == init:
> +    print_err("init", p[0].file, int(p[0].line))
> +    cocci.include_match(False)
> +
> +@script:python@
> +drv_probe << has_probe.drv_probe;
> +p << hascall.p;
> +@@
> +
> +if p[0].current_element == drv_probe:
> +    print_err("probe", p[0].file, int(p[0].line))
> +    cocci.include_match(False)
> +
> +@script:python@
> +p << hascall.p;
> +@@
> +
> +add_if_not_present(p[0].current_element, p[0].file, p[0].line)
> +
> +@hasrecall depends on after_start@
> +position p;
> +identifier virtual.fn;
> +@@
> +
> +fn@p(...)
> +
> +@script:python@
> +init << defines_module_init.init;
> +p << hasrecall.p;
> +starter << virtual.starter;
> +@@
> +
> +if p[0].current_element == init:
> +    print_err("init", p[0].file, int(starter))
> +    cocci.include_match(False)
> +
> +@script:python@
> +drv_probe << has_probe.drv_probe;
> +p << hasrecall.p;
> +starter << virtual.starter;
> +@@
> +
> +if p[0].current_element == drv_probe:
> +    print_err("probe", p[0].file, int(starter))
> +    cocci.include_match(False)
> +
> +@script:python@
> +p << hasrecall.p;
> +starter << virtual.starter;
> +@@
> +
> +add_if_not_present(p[0].current_element, p[0].file, starter)
> --
> 2.8.2
>



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch