arm64: entry: fix ABBA deadlock when el1_dbg preempts rq->lock context

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7DAV3
CVE: NA

--------------------------------

When arm64 enters el1_dbg, it will hold rcu_node lock. If rq_lock critical
section is preempted by el1_dbg, it may cause an ABBA deadlock. The
scenario is as follows:

CPU0 			CPU1
---- 			----
process			context rcu_gp_fqs()

lock(&rq->lock);
			lock(rcu_node_0);
			lock(&rq->lock);
//el1_dbg()
lock(rcu_node_0);

rcu_nmi_enter() do not hold rcu_node in the nmi context, so fix this issue
by keeping the same logical for el1_dbg without marking el1_dbg as nmi.

Fixes: d8bb6718 ("arm64: Make debug exception handlers visible from RCU")
Signed-off-by: NYu Liao <liaoyu15@huawei.com>

arch/arm64/kernel/entry-common.c

@@ -17,6 +17,7 @@
 #include <asm/mmu.h>
 #include <asm/sysreg.h>
 
+static DEFINE_PER_CPU(int, dbg_count);
 /*
  * This is intended to match the logic in irqentry_enter(), handling the kernel
  * mode transitions only.
@@ -150,10 +151,16 @@ static void noinstr el1_inv(struct pt_regs *regs, unsigned long esr)
 	exit_to_kernel_mode(regs);
 }
 
+int in_dbg(void)
+{
+	return this_cpu_read(dbg_count) > 0;
+}
+
 static void noinstr arm64_enter_el1_dbg(struct pt_regs *regs)
 {
 	regs->lockdep_hardirqs = lockdep_hardirqs_enabled();
 
+	this_cpu_inc(dbg_count);
 	lockdep_hardirqs_off(CALLER_ADDR0);
 	rcu_nmi_enter();
 
@@ -172,6 +179,7 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs)
 	rcu_nmi_exit();
 	if (restore)
 		lockdep_hardirqs_on(CALLER_ADDR0);
+	this_cpu_dec(dbg_count);
 }
 
 static void noinstr el1_dbg(struct pt_regs *regs, unsigned long esr)

include/linux/preempt.h

@@ -352,4 +352,6 @@ static __always_inline void migrate_enable(void)
 	preempt_enable();
 }
 
+int in_dbg(void);
+
 #endif /* __LINUX_PREEMPT_H */

kernel/panic.c

@@ -761,3 +761,8 @@ static int __init panic_on_taint_setup(char *s)
 	return 0;
 }
 early_param("panic_on_taint", panic_on_taint_setup);
+
+int __weak in_dbg(void)
+{
+	return 0;
+}

kernel/rcu/tree.c

@@ -957,7 +957,7 @@ void __rcu_irq_enter_check_tick(void)
 	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
 
 	// If we're here from NMI there's nothing to do.
-	if (in_nmi())
+	if (in_nmi() || in_dbg())
 		return;
 
 	RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),