linux-kernel - [PATCH 1/2] regulator: dummy: force synchronous probing

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Message-ID: <20250310163302.15276-1-ceggers@arri.de>
Date: Mon, 10 Mar 2025 17:33:01 +0100
From: Christian Eggers <ceggers@...i.de>
To: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
	Douglas Anderson <dianders@...omium.org>
CC: <linux-kernel@...r.kernel.org>, Christian Eggers <ceggers@...i.de>,
	<stable@...r.kernel.org>
Subject: [PATCH 1/2] 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@...r.kernel.org
Fixes: 259b93b21a9f ("regulator: Set PROBE_PREFER_ASYNCHRONOUS for drivers that existed in 4.14")
Signed-off-by: Christian Eggers <ceggers@...i.de>
---
 drivers/regulator/dummy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/regulator/dummy.c b/drivers/regulator/dummy.c
index 5b9b9e4e762d..9f59889129ab 100644
--- 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,
 	},
 };

-- 
2.43.0