Re: [PATCH] ARM: enable interrupts when arm_notify_die() is handling user mode errors

[Sebastian Andrzej Siewior]

On 2026-06-25 15:35:22 [+0800], Xie Yuanbin wrote:
> For lastest linux-next kernel, with default multi_v7_defconfig, and
> setting CONFIG_PREEMPT_RT=y, CONFIG_DEBUG_ATOMIC_SLEEP=y, and
> CONFIG_PERF_EVENTS=n. When the user program executes bkpt
> instruction, the following WARN will be triggered:
> ```log
> [    3.677825] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> [    3.678002] in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 84, name: test
> [    3.678036] preempt_count: 0, expected: 0
> [    3.678078] RCU nest depth: 0, expected: 0
> [    3.678864] CPU: 0 UID: 0 PID: 84 Comm: test Tainted: G        W           7.1.0-next-20260623 #45 PREEMPT_RT
> [    3.679067] Tainted: [W]=WARN
> [    3.679088] Hardware name: Generic DT based system
> [    3.679198] Call trace:
> [    3.679695]  unwind_backtrace from show_stack+0x10/0x14
> [    3.680363]  show_stack from dump_stack_lvl+0x50/0x5c
> [    3.680377]  dump_stack_lvl from __might_resched+0x160/0x174
> [    3.680393]  __might_resched from rt_spin_lock+0x38/0x138
> [    3.680425]  rt_spin_lock from force_sig_info_to_task+0x1c/0x11c
> [    3.680438]  force_sig_info_to_task from force_sig_fault+0x44/0x64
> [    3.680450]  force_sig_fault from do_PrefetchAbort+0x94/0x9c
> [    3.680461]  do_PrefetchAbort from ret_from_exception+0x0/0x20
> [    3.680513] Exception stack(0xf0ab5fb0 to 0xf0ab5ff8)
> [    3.680653] 5fa0:                                     00000000 bed32e94 bed32e9c 00037954
> [    3.680672] 5fc0: 00000002 00000001 bed32e94 0009d590 00000000 bed32e9c 00000002 00000000
> [    3.680682] 5fe0: bed32d48 bed32d38 00037a00 00037958 60000010 ffffffff
> ```

I don't think this required information as it is obvious. At the very
least you could trim it the needed parts if considered needed.

> When PREEMPT_RT is enabled, force_sig_info() requires interrupts to be
> enabled. Enable interrupts when arm_notify_die() is handling user mode
> errors to fix the issue.
> 
> Fixes: c6e61c06d606 ("ARM: 9463/1: Allow to enable RT")
> 
> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: Russell King (Oracle) <rmk+kernel@xxxxxxxxxxxxxxx>
> Signed-off-by: Xie Yuanbin <xieyuanbin1@xxxxxxxxxx>

So I did test the 32bit case on arm64 while testing/ backporting the
breakpoint handling there but apparently did not try it on real
arm32.

For "asm("BKPT #0");" the SIGTRAP is not raised instead I get just
| 8<--- cut here ---
| Unhandled prefetch abort: debug event (0x222) at 0x00000000

on the kernel side and a "Bus error" on userland side.

So
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

for this but actual breakpoint handling might be broken or is it just
me? But then your stack trace looks like mine so :/

Sebastian