[PATCH v2] ARM: enable interrupts when unhandled user faults are triggered

[Xie Yuanbin]

PREEMPT_RT requires interrupts to be enabled when sending signals.

When do_DataAbort()/do_PrefetchAbort() triggers unhandled user faults,
that is `inf->fn()` return a non-zero value, and the interrupts are not
enabled within the hook function, force_sig_fault() will be called
with interrupts disabled.

This can be triggered by user programs executing the bkpt instruction,
with kernel config CONFIG_PERF_EVENTS=n.

Enable interrupts in do_DataAbort()/do_PrefetchAbort() when unhandled
user faults are triggered to fix the issue.

Fixes: c6e61c06d606 ("ARM: 9463/1: Allow to enable RT")

Suggested-by: Russell King <linux@xxxxxxxxxxxxxxx>
Suggested-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Xie Yuanbin <xieyuanbin1@xxxxxxxxxx>
---
v1->v2: https://lore.kernel.org/20260625073522.182503-1-xieyuanbin1@xxxxxxxxxx
  - Move local_irq_enable() from arm_notify_die() to
    do_DataAbort()/do_PrefetchAbort()

 arch/arm/mm/fault.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index e62cc4be5adf..c68677503532 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -633,6 +633,9 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
 		return;
 
+	if (likely(user_mode(regs)))
+		local_irq_enable();
+
 	pr_alert("8<--- cut here ---\n");
 	pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
 		inf->name, fsr, addr);
@@ -663,6 +666,9 @@ do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
 	if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
 		return;
 
+	if (likely(user_mode(regs)))
+		local_irq_enable();
+
 	pr_alert("8<--- cut here ---\n");
 	pr_alert("Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
 		inf->name, ifsr, addr);
-- 
2.53.0