[Linux-kernel-mentees] [PATCH] doc: listRCU: Add some more listRCU patterns in the kernel
frextrite at gmail.com
Wed Dec 4 08:24:12 UTC 2019
On Tue, Dec 03, 2019 at 06:41:32AM -0700, Jonathan Corbet wrote:
> On Tue, 3 Dec 2019 12:09:43 +0530
> Amol Grover <frextrite at gmail.com> wrote:
> > - Add more information about listRCU patterns taking examples
> > from audit subsystem in the linux kernel.
> > - The initially written audit examples are kept, even though they are
> > slightly different in the kernel.
> > - Modify inline text for better passage quality.
> > - Fix typo in code-blocks and improve code comments.
> > - Add text formatting (italics, bold and code) for better emphasis.
> Thanks for improving the documentation! I'll leave the RCU stuff to the
> experts, but I do have one request...
> > +When a process exits, ``release_task()`` calls ``list_del_rcu(&p->tasks)`` under
> > +``tasklist_lock`` writer lock protection, to remove the task from the list of
> > +all tasks. The ``tasklist_lock`` prevents concurrent list additions/removals
> > +from corrupting the list. Readers using ``for_each_process()`` are not protected
> > +with the ``tasklist_lock``. To prevent readers from noticing changes in the list
> > +pointers, the ``task_struct`` object is freed only after one or more grace
> > +periods elapse (with the help of ``call_rcu()``). This deferring of destruction
> > +ensures that any readers traversing the list will see valid ``p->tasks.next``
> > +pointers and deletion/freeing can happen in parallel with traversal of the list.
> > +This pattern is also called an **existence lock**, since RCU pins the object in
> > +memory until all existing readers finish.
> Please don't put function names as literal text. If you just say
> call_rcu(), it will be formatted correctly and cross-linked to the
> appropriate kerneldoc entry. Saying ``call_rcu()`` defeats that and
> clutters the plain-text reading experience.
The cross-reference of the functions should be done automatically by sphinx
while generating HTML, right? But when compiled none of the functions were
cross-referenced hence "``" was added around the methods (and other symbols)
to distinguish them from normal text.
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