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Currently reference counts are implemented by locking service_spinlock and then incrementing the service's ->ref_count field, calling kfree() when the last reference has been dropped. But at the same time, there's code in multiple places that dereferences pointers to services without having a reference, so there could be a race there. It should be possible to avoid taking any lock in unlock_service() or service_release() because we are setting a single array element to NULL, and on service creation, a mutex is locked before looking for a NULL spot to put the new service in. Using a struct kref and RCU-delaying the freeing of services fixes this race condition while still making it possible to skip grabbing a reference in many places. Also it avoids the need to acquire a single spinlock when e.g. taking a reference on state->services[i] when somebody else is in the middle of taking a reference on state->services[j]. Signed-off-by: Marcelo Diop-Gonzalez <marcgonzalez@google.com> Link: https://lore.kernel.org/r/3bf6f1ec6ace64d7072025505e165b8dd18b25ca.1581532523.git.marcgonzalez@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.