[OE-core] [PATCH RFC] module.bbclass: Fix potential do_compile/do_make_scripts race condition

[Paul Barker]

I ran into a race condition building multiple external modules against a 3.10.y
series kernel using the dylan branch of OpenEmbedded. This is difficult to
reproduce as it requires very specific timing: the do_make_scripts task for one
module was linking the modpost script whilst the do_compile task for another
module was attempting to use the modpost script. This resulted in a permission
error:

ERROR: Function failed: do_compile (see /home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/work/amc_d24a4-oe-linux-gnueabi/ti-hplib-mod/01.01.00.04-r3d/temp/log.do_compile.25434 for further information)
ERROR: Logfile of failure stored in: /home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/work/amc_d24a4-oe-linux-gnueabi/ti-hplib-mod/01.01.00.04-r3d/temp/log.do_compile.25434
Log data follows:
| DEBUG: Executing shell function do_compile
| make -C /home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/sysroots/amc-d24a4/usr/src/kernel M=$PWD clean
| make[1]: Entering directory `/home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/sysroots/amc-d24a4/usr/src/kernel'
| make[1]: Leaving directory `/home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/sysroots/amc-d24a4/usr/src/kernel'
| make -C /home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/sysroots/amc-d24a4/usr/src/kernel M=$PWD modules
| make[1]: Entering directory `/home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/sysroots/amc-d24a4/usr/src/kernel'
|   CC [M]  /home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/work/amc_d24a4-oe-linux-gnueabi/ti-hplib-mod/01.01.00.04-r3d/git/ti/runtime/hplib/module/hplibmod.o
|   Building modules, stage 2.
|   MODPOST 1 modules
| /bin/sh: scripts/mod/modpost: Permission denied
| make[2]: *** [__modpost] Error 126
| make[1]: *** [modules] Error 2
| make[1]: Leaving directory `/home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/sysroots/amc-d24a4/usr/src/kernel'
| make: *** [default] Error 2
| ERROR: Function failed: do_compile (see /home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/build/tmp/work/amc_d24a4-oe-linux-gnueabi/ti-hplib-mod/01.01.00.04-r3d/temp/log.do_compile.25434 for further information)
ERROR: Task 1284 (/home/COMMAGILITY/paul.barker/linux-bsp/work-1.0.1/ca-linux-bsp/meta-mcsdk/meta-arago-extras/recipes-bsp/ti-hplib/ti-hplib-mod_git.bb, do_compile) failed with exit code '1'

Later kernel versions do not rebuild the modpost script every time that 'make
scripts' is invoked so they should be safe from this particular failure. However
I'm not convinced that running 'make scripts' whilst also building an
out-of-tree module is always safe on later kernels and there is always the
potential for vendor kernels to have different behaviour here.

Although this was seen on the dylan branch the behaviour of master and jethro
looks to be the same here - do_make_scripts is locked so that only one instance
of it may run at one time but there is nothing to prevent one instance of
do_make_scripts running at the same time as an instance of do_compile.

The patch I'm sending attempts to solve this issue by locking the do_compile
task with the same lockfile as the do_make_scripts task in module.bbclass so
that an instance of do_copile can't run at the same time as an instance of
do_make_scripts. I don't know enough about the task locking to guarantee that
this is the right solution or to be able to test that it works as expected so
I'm marking the patch as an RFC.

Please let me know if this is the right approach and if there is any easy way to
test this.

Paul Barker (1):
  module.bbclass: Fix potential do_compile/do_make_scripts race
    condition

 meta/classes/module.bbclass | 4 ++++
 1 file changed, 4 insertions(+)

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1.8.3.1