chip/stm32: Only use a mutex when not in interrupt context

Mutexes shouldn't be used in interrupt context. An ASSERT was added in
mutex_lock to verify this commit
e6956209119d2b2c1f45401855019e3a0a2f7dd5.

There are cases where bkpdata_write can be called from an interrupt
context, such as this stack trace that occurs when adding entropy from
RO on dartmonkey/icetower (stack captured with Segger J-Trace):

> rollbackaddent 1234

panic_assert_fail panic_output.c:132
mutex_lock task.c:889
bkpdata_write bkpdata.c:35
bkpdata_write bkpdata.c:24
bkpdata_write_reset_flags bkpdata.c:86
chip_save_reset_flags system.c:366
system_reset system.c:366
panic_reboot panic_output.c:114
report_panic panic.c:339
exception_panic panic.c:350

Validation of the fix was checked with the "rollback_region1" unit test,
which failed before the change and works after.

BRANCH=none
BUG=b:170147314
TEST=./test/run_device_tests.py -b dartmonkey -t rollback_region1

Signed-off-by: Tom Hughes <tomhughes@chromium.org>
Change-Id: Ie5509ec024e94b48c786199ccbb81ce93fafe547
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2462545
Reviewed-by: Edward Hill <ecgh@chromium.org>

0 files changed, 0 insertions, 0 deletions