[PATCH] ARM: shmobile: rcar-gen2: Fix deadlock in regulator quirk

From: Geert Uytterhoeven
Date: Wed Jul 12 2017 - 10:45:35 EST

Simon Horman reported that Koelsch and Lager hang during boot, and
bisected this to commit 1c3c5eab171590f8 ("sched/core: Enable
might_sleep() and smp_processor_id() checks early").

The da9063/da9210 regulator quirk for R-Car Gen2 boards uses a bus
notifier, and unregisters the notifier when it is no longer needed.
However, a notifier must not be unregistered from within the call chain.

This bug went unnoticed, as blocking_notifier_chain_unregister() didn't
take the semaphore during early boot. The aforementioned commit changed
that behavior, leading to a deadlock.

Fix this by removing the call to bus_unregister_notifier(), and keeping
local completion state instead.

Reported-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>
Fixes: 663fbb52159cca6f ("ARM: shmobile: R-Car Gen2: Add da9063/da9210 regulator quirk")
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c b/arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c
index 73e3adbc133096ec..44438f344dc80f9c 100644
--- a/arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c
+++ b/arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c
@@ -67,8 +67,12 @@ static int regulator_quirk_notify(struct notifier_block *nb,
struct device *dev = data;
struct i2c_client *client;
+ static bool done;
u32 mon;

+ if (done)
+ return 0;
mon = ioread32(irqc + IRQC_MONITOR);
dev_dbg(dev, "%s: %ld, IRQC_MONITOR = 0x%x\n", __func__, action, mon);
@@ -99,7 +103,7 @@ static int regulator_quirk_notify(struct notifier_block *nb,
dev_info(dev, "IRQ2 is not asserted, removing quirk\n");

- bus_unregister_notifier(&i2c_bus_type, nb);
+ done = true;
return 0;