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It seems that alloc_retstack_tasklist() can also take a lockless approach for scanning the tasklist, instead of using the big global tasklist_lock. For this we also kill another deprecated and rcu-unsafe tsk->thread_group user replacing it with for_each_process_thread(), maintaining semantics. Here tasklist_lock does not protect anything other than the list against concurrent fork/exit. And considering that the whole thing is capped by FTRACE_RETSTACK_ALLOC_SIZE (32), it should not be a problem to have a pontentially stale, yet stable, list. The task cannot go away either, so we don't risk racing with ftrace_graph_exit_task() which clears the retstack. The tsk->ret_stack management is not protected by tasklist_lock, being serialized with the corresponding publish/subscribe barriers against concurrent ftrace_push_return_trace(). In addition this plays nicer with cachelines by avoiding two atomic ops in the uncontended case. Link: https://lkml.kernel.org/r/20200907013326.9870-1-dave@stgolabs.net Acked-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.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.