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Currently, concurrent writes to sysfs entries leave the possibility for race conditions within the devfreq framework. For example, concurrently executing max_freq_store and governor_store can result in attempting to perform an update_devfreq() before the new governor's start handler can be executed. A more concrete case is a race between polling_interval_store and governor_store. Because no lock is used after calling into the event handler of the old governor and there's nothing preventing work from being queued after the monitor is stopped, it's possible to accidentally cause delayed work to be queued on the governor being switched to. This can be seen if you create two threads, one which changes a device's governor between simple_ondemand and performance, and one which changes its polling interval between 45 and 50. All of these races can be addressed with the introduction of a lock that prevents sysfs operations from interleaving in this fashion. Change-Id: Ia6887dcb2d69dc2576837a6c09fed55a28943abc Signed-off-by: Jonathan Avila <avilaj@codeaurora.org> Signed-off-by: Rama Aparna Mallavarapu <aparnam@codeaurora.org> Bug: 152343889 (cherry picked from commit 78fdd25c1abb1f23f43243f09c3d81cccaa844bc) [saravanak Fixed some conflicts] Signed-off-by: Saravana Kannan <saravanak@google.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
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.