Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12)

[Steven Rostedt]

On Thu, 29 Mar 2018 14:02:33 -0400 (EDT)
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:

> Currently, anyone using ptrace on a process has pretty much given up all
> hopes of performance. Processes will use rseq to gain performance, not the
> opposite, so this deterioration will be unwelcome.

The ptrace path has nothing to do with ptrace anymore, and probably be
hard to notice the performance hit. You simply set a TIF flag, and on
exit of the syscall it jumps to a path that checks special cases
(tracing system calls being one of them). It's called the ptrace path
because ptrace was the first one to use it (I'm guessing, I haven't
actually looked at the history).

This is used to add any system call checks that are not done during
normal operation. And this certainly falls under that category.

-- Steve