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

[Simon Horman]

From: Geert Uytterhoeven 

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 
Fixes: 663fbb52159cca6f ("ARM: shmobile: R-Car Gen2: Add da9063/da9210 
regulator quirk")
Signed-off-by: Geert Uytterhoeven 
Signed-off-by: Simon Horman 
---
 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 73e3adbc1330..44438f344dc8 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);
if (mon & REGULATOR_IRQ_MASK)
@@ -99,7 +103,7 @@ static int regulator_quirk_notify(struct notifier_block *nb,
 remove:
dev_info(dev, "IRQ2 is not asserted, removing quirk\n");
 
-   bus_unregister_notifier(_bus_type, nb);
+   done = true;
iounmap(irqc);
return 0;
 }
-- 
2.1.4

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

[Simon Horman]

On Wed, Jul 12, 2017 at 04:45:20PM +0200, Geert Uytterhoeven wrote:
> 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 
> Fixes: 663fbb52159cca6f ("ARM: shmobile: R-Car Gen2: Add da9063/da9210 
> regulator quirk")
> Signed-off-by: Geert Uytterhoeven 

Sorry for the delay, I have applied this as a fix for v4.13.

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

[Geert Uytterhoeven]

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 
Fixes: 663fbb52159cca6f ("ARM: shmobile: R-Car Gen2: Add da9063/da9210 
regulator quirk")
Signed-off-by: Geert Uytterhoeven 
---
 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);
if (mon & REGULATOR_IRQ_MASK)
@@ -99,7 +103,7 @@ static int regulator_quirk_notify(struct notifier_block *nb,
 remove:
dev_info(dev, "IRQ2 is not asserted, removing quirk\n");
 
-   bus_unregister_notifier(_bus_type, nb);
+   done = true;
iounmap(irqc);
return 0;
 }
-- 
2.7.4