[RFC PATCH] extcon: Fix sleeping in atomic context after connecting USB cable

From: Krzysztof Kozlowski
Date: Fri Sep 26 2014 - 07:50:55 EST

Kernel built with extcon and charger-manager.

After connecting the USB cable sleeping function was called from atomic
context:
[ 63.328648] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:586
[ 63.331449] in_atomic(): 1, irqs_disabled(): 128, pid: 906, name: kworker/1:2
[ 63.338562] INFO: lockdep is turned off.
[ 63.342468] irq event stamp: 0
[ 63.345507] hardirqs last enabled at (0): [< (null)>] (null)
[ 63.351495] hardirqs last disabled at (0): [<c00246c8>] copy_process.part.46+0x4a0/0x1684
[ 63.359654] softirqs last enabled at (0): [<c00246c8>] copy_process.part.46+0x4a0/0x1684
[ 63.367813] softirqs last disabled at (0): [< (null)>] (null)
[ 63.373802] Preemption disabled at:[< (null)>] (null)
[ 63.379097]
[ 63.380581] CPU: 1 PID: 906 Comm: kworker/1:2 Not tainted 3.16.2-00822-g691a2ac4e574 #954
[ 63.388743] Workqueue: events max14577_muic_irq_work
[ 63.393707] [<c00167a4>] (unwind_backtrace) from [<c0012c08>] (show_stack+0x10/0x14)
[ 63.401422] [<c0012c08>] (show_stack) from [<c06232ec>] (dump_stack+0x70/0xbc)
[ 63.408625] [<c06232ec>] (dump_stack) from [<c0629d0c>] (mutex_lock_nested+0x24/0x410)
[ 63.416525] [<c0629d0c>] (mutex_lock_nested) from [<c0354474>] (regmap_read+0x30/0x60)
[ 63.424424] [<c0354474>] (regmap_read) from [<c0406b84>] (max14577_charger_get_property+0x1e4/0x250)
[ 63.433535] [<c0406b84>] (max14577_charger_get_property) from [<c0403834>] (is_ext_pwr_online+0x30/0x6c)
[ 63.442994] [<c0403834>] (is_ext_pwr_online) from [<c0404a54>] (charger_extcon_notifier+0x40/0x70)
[ 63.451934] [<c0404a54>] (charger_extcon_notifier) from [<c044cbe4>] (_call_per_cable+0x40/0x4c)
[ 63.460704] [<c044cbe4>] (_call_per_cable) from [<c0051560>] (notifier_call_chain+0x64/0x128)
[ 63.469209] [<c0051560>] (notifier_call_chain) from [<c0051640>] (raw_notifier_call_chain+0x18/0x20)
[ 63.478321] [<c0051640>] (raw_notifier_call_chain) from [<c044d0fc>] (extcon_update_state+0xa8/0x204)
[ 63.487522] [<c044d0fc>] (extcon_update_state) from [<c044e5f8>] (max14577_muic_chg_handler+0xdc/0x180)
[ 63.496897] [<c044e5f8>] (max14577_muic_chg_handler) from [<c044e924>] (max14577_muic_irq_work+0x7c/0xd8)
[ 63.506445] [<c044e924>] (max14577_muic_irq_work) from [<c004480c>] (process_one_work+0x198/0x66c)
[ 63.515385] [<c004480c>] (process_one_work) from [<c0044d4c>] (worker_thread+0x38/0x564)
[ 63.523455] [<c0044d4c>] (worker_thread) from [<c004c4ec>] (kthread+0xcc/0xe8)
[ 63.530661] [<c004c4ec>] (kthread) from [<c000f1f8>] (ret_from_fork+0x14/0x3c)
[ 63.543926] charger_manager: Set current limit of CHARGER : 450000uA ~ 450000uA
[ 63.548870] extcon-port jack: jack event CHGDET=usb
[ 63.550592] extcon-port jack: jack event CHGDET=charger
[ 64.188607] charger-manager charger-manager@0: Failed to get battery temperature
[ 64.200684] charger-manager charger-manager@0: CHARGING

The first sleeping function is is_ext_pwr_online()
(drivers/power/charger-manager.c). The atomic context initiating the
flow is set up in extcon_update_state() (drivers/extcon/extcon-class.c).

The extcon_update_state() uses spin locks which are not necessary
because the function is not called from interrupt service routines.
Instead, the extcon_update_state() is called from:
1. Threaded interrupt handlers.
2. Work queues.

Replace the spin lock with mutex and update the documentation of this
function.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>
---
drivers/extcon/extcon-class.c | 15 ++++++++-------
include/linux/extcon.h | 3 ++-
2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/extcon/extcon-class.c b/drivers/extcon/extcon-class.c
index 4c2f2c543bb7..7485600baeff 100644
--- a/drivers/extcon/extcon-class.c
+++ b/drivers/extcon/extcon-class.c
@@ -201,6 +201,8 @@ static ssize_t cable_state_show(struct device *dev,
*
* Note that the notifier provides which bits are changed in the state
* variable with the val parameter (second) to the callback.
+ *
+ * The function may sleep thus may not be called from atomic context.
*/
int extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state)
{
@@ -210,16 +212,15 @@ int extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state)
char *envp[3];
int env_offset = 0;
int length;
- unsigned long flags;

- spin_lock_irqsave(&edev->lock, flags);
+ mutex_lock(&edev->lock);

if (edev->state != ((edev->state & ~mask) | (state & mask))) {
u32 old_state = edev->state;

if (check_mutually_exclusive(edev, (edev->state & ~mask) |
(state & mask))) {
- spin_unlock_irqrestore(&edev->lock, flags);
+ mutex_unlock(&edev->lock);
return -EPERM;
}

@@ -248,20 +249,20 @@ int extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state)
}
envp[env_offset] = NULL;
/* Unlock early before uevent */
- spin_unlock_irqrestore(&edev->lock, flags);
+ mutex_unlock(&edev->lock);

kobject_uevent_env(&edev->dev.kobj, KOBJ_CHANGE, envp);
free_page((unsigned long)prop_buf);
} else {
/* Unlock early before uevent */
- spin_unlock_irqrestore(&edev->lock, flags);
+ mutex_unlock(&edev->lock);

dev_err(&edev->dev, "out of memory in extcon_set_state\n");
kobject_uevent(&edev->dev.kobj, KOBJ_CHANGE);
}
} else {
/* No changes */
- spin_unlock_irqrestore(&edev->lock, flags);
+ mutex_unlock(&edev->lock);
}

return 0;
@@ -834,7 +835,7 @@ int extcon_dev_register(struct extcon_dev *edev)
ret = class_compat_create_link(switch_class, &edev->dev, NULL);
#endif /* CONFIG_ANDROID */

- spin_lock_init(&edev->lock);
+ mutex_init(&edev->lock);

RAW_INIT_NOTIFIER_HEAD(&edev->nh);

diff --git a/include/linux/extcon.h b/include/linux/extcon.h
index 36f49c405dfb..166f42cecd5a 100644
--- a/include/linux/extcon.h
+++ b/include/linux/extcon.h
@@ -26,6 +26,7 @@
#include <linux/device.h>
#include <linux/notifier.h>
#include <linux/sysfs.h>
+#include <linux/mutex.h>

#define SUPPORTED_CABLE_MAX 32
#define CABLE_NAME_MAX 30
@@ -125,7 +126,7 @@ struct extcon_dev {
struct raw_notifier_head nh;
struct list_head entry;
int max_supported;
- spinlock_t lock; /* could be called by irq handler */
+ struct mutex lock;
u32 state;

/* /sys/class/extcon/.../cable.n/... */
--
1.9.1

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