From c9ccaa0cac3fc8e7d17a668aabfdf632c7c0517a Mon Sep 17 00:00:00 2001 From: Tirupathi Reddy Date: Wed, 12 Jul 2017 17:08:13 +0530 Subject: [PATCH] regulator: core: fix a possible race in disable_work handling 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_unlock(&rdev->mutex); ..... queue_delayed_work(...) mutex_lock(&rdev->mutex); ..... 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 Signed-off-by: Mark Brown --- 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 e567fa54980b..9f4d484eb25d 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); -- 2.20.1