A race condition between queueing and processing the disable_work
instances results in having a work instance in the queue and the
deferred_disables variable of regulator device structure having a
value '0'. If no new regulator_disable_deferred() call later from
clients, the deferred_disables variable value remains '0' and hits
BUG() in regulator_disable_work() when the queued instance scheduled
for processing the work.
The race occurs as below:
Core-0 Core-1
..... /* deferred_disables = 2 */ .....
..... /* disable_work is queued */ .....
..... .....
regulator_disable_deferred: regulator_disable_work:
mutex_lock(&rdev->mutex); .....
rdev->deferred_disables++; mutex_lock(&rdev->mutex);
mutex_unlock(&rdev->mutex); .....
queue_delayed_work(...) count =rdev->deferred_disables;
..... rdev->deferred_disables = 0;
..... .....
..... mutex_unlock(&rdev->mutex);
..... .....
..... return;
..... .....
/* No new regulator_disable_deferred() calls from clients */
/* The newly queued instance is scheduled for processing */
..... .....
regulator_disable_work:
.....
mutex_lock(&rdev->mutex);
BUG_ON(!rdev->deferred_disables); /* deferred_disables = 0 */
The race is fixed by removing the work instance that is queued while
processing the previous queued instance. Cancel the newly queued instance
from disable_work() handler just after reset the deferred_disables variable
to value '0'. Also move the work queueing step before mutex_unlock in
regulator_disable_deferred().
Also use mod_delayed_work() in the pace of queue_delayed_work() as
queue_delayed_work() always uses the delay requested in the first call
when multiple consumers call regulator_disable_deferred() close in time
and does not guarantee the semantics of regulator_disable_deferred().
Signed-off-by: Tirupathi Reddy <tirupath@xxxxxxxxxxxxxx>
---
drivers/regulator/core.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index e567fa5..9f4d484 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -2396,6 +2396,14 @@ static void regulator_disable_work(struct work_struct *work)
count = rdev->deferred_disables;
rdev->deferred_disables = 0;
+ /*
+ * Workqueue functions queue the new work instance while the previous
+ * work instance is being processed. Cancel the queued work instance
+ * as the work instance under processing does the job of the queued
+ * work instance.
+ */
+ cancel_delayed_work(&rdev->disable_work);
+
for (i = 0; i < count; i++) {
ret = _regulator_disable(rdev);
if (ret != 0)
@@ -2439,10 +2447,10 @@ int regulator_disable_deferred(struct regulator *regulator, int ms)
mutex_lock(&rdev->mutex);
rdev->deferred_disables++;
+ mod_delayed_work(system_power_efficient_wq, &rdev->disable_work,
+ msecs_to_jiffies(ms));
mutex_unlock(&rdev->mutex);
- queue_delayed_work(system_power_efficient_wq, &rdev->disable_work,
- msecs_to_jiffies(ms));
return 0;
}
EXPORT_SYMBOL_GPL(regulator_disable_deferred);
--
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