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

From: "Luis Claudio R. Goncalves" <[email-masked]>
Date: Wed, 20 May 2026 08:23:49 -0300

On Wed, May 20, 2026 at 08:19:20AM +0200, Sebastian Andrzej Siewior wrote:
> On 2026-05-19 18:25:24 [-0400], Waiman Long wrote:
> > Commit d8bb6718c4db ("arm64: Make debug exception handlers visible from
> > RCU") introduces debug_exception_enter() and debug_exception_exit()
> > where preemption is explicitly disabled. With a PREEMPT_RT debug kernel,
> > the following bug report can happen.
> …
> 
> What kernel is this? I have backport (which is being tested) for v6.6
> and v6.12, the patches are from v6.17-rc1.

Sebastian, hardware breakpoint and watchpoint handlers still call
debug_exception_exit() and disable preemption on aarch64. That should
happen on v7.1-rc4 indeed. The suggestion was to mimic what x86_64 does
with notify_die() -> hw_breakpoint_exceptions_notify(). In ARM
hw_breakpoint_exceptions_notify() is a stub that always returns
NOTIFY_DONE.

Luis

> Sebastian
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