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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 <tirupath@codeaurora.org> Signed-off-by: Mark Brown <broonie@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.