[RFC PATCH v2 2/2] ARM/mm/fault: Enable interrupts before sending signal

[Xie Yuanbin]

From: xieyuanbin1 <xieyuanbin1@xxxxxxxxxx>

Sending a signal requires to acquire sighand_struct::siglock which is a
spinlock_t. On PREEMPT_RT spinlock_t becomes a sleeping spin lock which
requires interrupts to be enabled. Since the calling context is user
land, interrupts must have been enabled so it is fine to enable them in
this case.

Signed-off-by: xieyuanbin1 <xieyuanbin1@xxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
This patch depends on patch
Link: https://lore.kernel.org/20251029155918.503060-6-bigeasy@xxxxxxxxxxxxx

The commit message is copy from:
Link: https://lore.kernel.org/20251029155918.503060-3-bigeasy@xxxxxxxxxxxxx

Maybe I should add:
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Or something else? Thanks!

 arch/arm/mm/fault.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 5c58072d8235..f8ee1854c854 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -184,10 +184,13 @@ __do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig,
 	struct task_struct *tsk = current;
 
 	if (addr > TASK_SIZE)
 		harden_branch_predictor();
 
+	if (IS_ENABLED(CONFIG_PREEMPT_RT))
+		local_irq_enable();
+
 #ifdef CONFIG_DEBUG_USER
 	if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) ||
 	    ((user_debug & UDBG_BUS)  && (sig == SIGBUS))) {
 		pr_err("8<--- cut here ---\n");
 		pr_err("%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
-- 
2.51.0