[OE-core] [RFC] Preventing race when compiling external kernel modules

[Anders Darander]

* Anders Darander <anders at chargestorm.se> [111014 09:55]:
> In our local tree, I've circumvented this race by applying a patch like
> [3]. (Well, we could likely have put the lock in do_make_scripts()
> instead of module_do_compile(), as we have done currently). Obviously,
> I'm not proposing to apply this patch, as it depends on lockfile from
> the procmail-package (host-package).

Just to confirm, it seems (after a very few tests) that it indeed is
enough to guard the do_make_scripts() with the lock.

However, the question on how to make the real solution remains...

Cheers,
Anders

> [3]
> $ cat 0001-module.bbclass-add-lock-to-prevent-error-bulding-ext.patch 
> From 9e23beb2ec499cdba04a11165efe8867ad4dc42a Mon Sep 17 00:00:00 2001
> From: Anders Darander <anders at chargestorm.se>
> Date: Mon, 10 Oct 2011 14:26:20 +0200
> Subject: [PATCH] module.bbclass: add lock to prevent error bulding ext
>  modules

> When external modules are built, certain files in STAGING_KERNEL_DIR
> might get rebuilt.
> This raises a potential race condition. Prevent this by using a lockfile
> to make external
> modules build in sequence.

> This patch is not applicable upstream, as it requires lockfile from
> procmail.

> Signed-off-by: Anders Darander <anders at chargestorm.se>
> ---
>  meta/classes/module.bbclass |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)

> diff --git a/meta/classes/module.bbclass b/meta/classes/module.bbclass
> index 572df0d..46abd81 100644
> --- a/meta/classes/module.bbclass
> +++ b/meta/classes/module.bbclass
> @@ -15,6 +15,8 @@ do_make_scripts() {
>  }

>  module_do_compile() {
> +       trap "rm -f ${STAGING_KERNEL_DIR}/external_modules.lock; exit 1"
> INT TERM EXIT
> +       lockfile -r-1 ${STAGING_KERNEL_DIR}/external_modules.lock
>         do_make_scripts
>         unset CFLAGS CPPFLAGS CXXFLAGS LDFLAGS
>         oe_runmake KERNEL_PATH=${STAGING_KERNEL_DIR}   \
> @@ -23,6 +25,8 @@ module_do_compile() {
>                    CC="${KERNEL_CC}" LD="${KERNEL_LD}" \
>                    AR="${KERNEL_AR}" \
>                    ${MAKE_TARGETS}
> +       rm -f ${STAGING_KERNEL_DIR}/external_modules.lock
> +        trap - INT TERM EXIT
>  }
>  module_do_install() {

-- 
Anders Darander
ChargeStorm AB / eStorm AB