c524a17312
commit b40341fad6cc2daa195f8090fd3348f18fff640a upstream. The first thing that the ftrace function callback helper functions should do is to check for recursion. Peter Zijlstra found that when "rcu_is_watching()" had its notrace removed, it caused perf function tracing to crash. This is because the call of rcu_is_watching() is tested before function recursion is checked and and if it is traced, it will cause an infinite recursion loop. rcu_is_watching() should still stay notrace, but to prevent this should never had crashed in the first place. The recursion prevention must be the first thing done in callback functions. Link: https://lore.kernel.org/r/20200929112541.GM2628@hirez.programming.kicks-ass.net Cc: stable@vger.kernel.org Cc: Paul McKenney <paulmck@kernel.org> Fixes: c68c0fa293417 ("ftrace: Have ftrace_ops_get_func() handle RCU and PER_CPU flags too") Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reported-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> 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.