Hi Doug,
On Thursday, 13 March 2025, 01:42:14 CET, Doug Anderson wrote:
Hi,
On Tue, Mar 11, 2025 at 2:18 AM Christian Eggers ceggers@arri.de wrote:
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
v2:
- no changes
drivers/regulator/dummy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
Not that it should really hurt, but do we need both commit cfaf53cb472e ("regulator: check that dummy regulator has been probed before using it") and this one? It seems like commit cfaf53cb472e ("regulator: check that dummy regulator has been probed before using it") would be sufficient and we don't really need to force the regulator to synchronous probing.
actually I also tested successfully without synchronous probing (only with checking that the dummy regulator has been probed) and this also worked fine (just to be sure, I also added a temporary delay in the dummy's probe routine). But as the dummy regulator doesn't rely on slow I/O, I felt that synchronous probing makes more sense than "busy-waiting" for it.
...not that I expect the dummy probing synchronously to be a big deal, I just want to make sure I understand.
-Doug
regards, Christian