[PATCH] arm64/entry: Don't disable preemption in debug_exception_enter() with RT kernel

[Sebastian Andrzej Siewior]

On 2026-05-29 21:51:06 [-0300], Luis Claudio R. Goncalves wrote:
> On Thu, May 28, 2026 at 05:35:54PM +0200, Sebastian Andrzej Siewior wrote:
> > On 2026-05-28 16:51:24 [+0200], To Waiman Long wrote:
> > > > The kernel backtrace is produced using the latest v7.1-rc4 kernel. There are
> > > > a number of changes to the debug_exception_enter() and
> > > > debug_exception_exit() functions over the years, but the preemption disable
> > > > code remains since its introduction in v5.3.
> > > 
> > > Let me look at this again.
> > 
> > So how do you reproduce this? The calls within debug_exception_enter()/
> > exit() look harmless or I miss the big thing here.
> > From your backtrace, you have brk_handler() and this is gone since
> > commit 31575e11ecf7e ("arm64: debug: split brk64 exception entry") which
> > is v6.17-rc1. I can use gdb with breakpoint handling.
> 
> Sebastian, in the original series Ada provided a few tests, including the
> two files I list below. Running that test in a v7.1-rc5 kernel with
> PREEMPT_RT and DEBUG_ATOMIC_SLEEP enabled, I get this backtrace:

This is a reminder to myself that I need to look at this since it does
not look solved with the breakpoint patches. But this is also perf.

Sebastian