[PATCH] arm64: entry: remove redundant IRQ flag tracing

[Will Deacon]

On Thu, Jan 07, 2021 at 02:53:10PM +0000, Mark Rutland wrote:
> All EL0 returns go via ret_to_user(), which masks IRQs and notifies
> lockdep and tracing before calling into do_notify_resume(). Therefore,
> there's no need for do_notify_resume() to call trace_hardirqs_off(), and
> the comment is stale. The call is simply redundant.
> 
> In ret_to_user() we call exit_to_user_mode(), which notifies lockdep and
> tracing the IRQs will be enabled in userspace, so there's no need for
> el0_svc_common() to call trace_hardirqs_on() before returning. Further,
> at the start of ret_to_user() we call trace_hardirqs_off(), so not only
> is this redundant, but it is immediately undone.
> 
> In addition to being redundant, the trace_hardirqs_on() in
> trace_hardirqs_on() isn't consistent with the HW state, and is liable to
> cause issues for any C code or instrumentation invoked before this is
> undone in ret_to_user().

I can't parse this final paragraph, but it seems to be the part which
justifies this as a fix. Please can you reword?

Will