On Wed, 18 Jun 2025 16:02:47 +0200 Peter Zijlstra <[email protected]> wrote:
> On Tue, Jun 10, 2025 at 08:54:25PM -0400, Steven Rostedt wrote: > > +/** > > + * unwind_deferred_trace - Produce a user stacktrace in faultable context > > + * @trace: The descriptor that will store the user stacktrace > > + * > > + * This must be called in a known faultable context (usually when entering > > + * or exiting user space). Depending on the available implementations > > + * the @trace will be loaded with the addresses of the user space > > stacktrace > > + * if it can be found. > > I am confused -- why would we ever want to call this on exiting > user-space, or rather kernel entry? > > I thought the whole point was to request a user trace while in-kernel, > and defer that to return-to-user. This code was broken out of the unwind deferred trace to be more stand alone. Actually, it should be renamed to unwind_faultable_trace() or something to denote that it must be called from a faultable context. When Josh made perf use the task_work directly, it used this function to do the trace as it handled the deferring. Note, a request from the gcc folks is to add a system call that gives the user space application a backtrace from its current location. This can be handy for debugging as it would be similar to how we use dump_stack(). This function would be used for that. -- Steve
