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[ Upstream commitbe28816971] Currently cgroup_get_from_path() and cgroup_get_from_id() grab cgroup_mutex before traversing the default hierarchy to find the kernfs_node corresponding to the path/id and then extract the linked cgroup. Since cgroup_mutex is still held, it is guaranteed that the cgroup will be alive and the reference can be taken on it. However similar guarantee can be provided without depending on the cgroup_mutex and potentially reducing avenues of cgroup_mutex contentions. The kernfs_node's priv pointer is RCU protected pointer and with just rcu read lock we can grab the reference on the cgroup without cgroup_mutex. So, remove cgroup_mutex from them. Signed-off-by: Shakeel Butt <shakeelb@google.com> Signed-off-by: Tejun Heo <tj@kernel.org> Stable-dep-of:df02452f3d("cgroup: cgroup_get_from_id() must check the looked-up kn is a directory") Signed-off-by: Sasha Levin <sashal@kernel.org>
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.
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.