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The shrinker resets the lazy callbacks counter in order to trigger the pending lazy queue flush though the rcuog kthread. The counter reset is protected by the ->nocb_lock against concurrent accesses...except for one of them. Here is a list of existing synchronized readers/writer: 1) The first lazy enqueuer (incrementing ->lazy_len to 1) does so under ->nocb_lock and ->nocb_bypass_lock. 2) The further lazy enqueuers (incrementing ->lazy_len above 1) do so under ->nocb_bypass_lock _only_. 3) The lazy flush checks and resets to 0 under ->nocb_lock and ->nocb_bypass_lock. The shrinker protects its ->lazy_len reset against cases 1) and 3) but not against 2). As such, setting ->lazy_len to 0 under the ->nocb_lock may be cancelled right away by an overwrite from an enqueuer, leading rcuog to ignore the flush. To avoid that, use the proper bypass flush API which takes care of all those details. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@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.