regulator: dummy: force synchronous probing

Sometimes I get a NULL pointer dereference at boot time in kobject_get()
with the following call stack:

anatop_regulator_probe()
 devm_regulator_register()
  regulator_register()
   regulator_resolve_supply()
    kobject_get()

By placing some extra BUG_ON() statements I could verify that this is
raised because probing of the 'dummy' regulator driver is not completed
('dummy_regulator_rdev' is still NULL).

In the JTAG debugger I can see that dummy_regulator_probe() and
anatop_regulator_probe() can be run by different kernel threads
(kworker/u4:*).  I haven't further investigated whether this can be
changed or if there are other possibilities to force synchronization
between these two probe routines.  On the other hand I don't expect much
boot time penalty by probing the 'dummy' regulator synchronously.

Cc: stable@vger.kernel.org
Fixes: 259b93b21a9f ("regulator: Set PROBE_PREFER_ASYNCHRONOUS for drivers that existed in 4.14")
Signed-off-by: Christian Eggers <ceggers@arri.de>
Link: https://patch.msgid.link/20250311091803.31026-1-ceggers@arri.de
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/regulator/dummy.c b/drivers/regulator/dummy.c
index 5b9b9e4e762d52151847bb1880377d51b04eeb9d..9f59889129abec9ab2066e68b3a52e3e8c814f76 100644 (file)
--- a/drivers/regulator/dummy.c
+++ b/drivers/regulator/dummy.c
@@ -60,7 +60,7 @@ static struct platform_driver dummy_regulator_driver = {
        .probe          = dummy_regulator_probe,
        .driver         = {
                .name           = "reg-dummy",
-               .probe_type     = PROBE_PREFER_ASYNCHRONOUS,
+               .probe_type     = PROBE_FORCE_SYNCHRONOUS,
        },
 };