cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2169516
Conflicts: A merge conflict in adding include file
	   <linux/context_tracking.h> to kernel/panic.c due to missing
	   upstream commit 23b36fec7e14 ("panic: use error_report_end
	   tracepoint on warnings") and commit 8b05aa263361 ("panic:
	   Expose "warn_count" to sysfs").

commit 5a5d7e9badd2cb8065db171961bd30bd3595e4b6
Author: Peter Zijlstra <peterz@infradead.org>
Date:   Thu, 26 Jan 2023 16:08:31 +0100

    cpuidle: lib/bug: Disable rcu_is_watching() during WARN/BUG

    In order to avoid WARN/BUG from generating nested or even recursive
    warnings, force rcu_is_watching() true during
    WARN/lockdep_rcu_suspicious().

    Notably things like unwinding the stack can trigger rcu_dereference()
    warnings, which then triggers more unwinding which then triggers more
    warnings etc..

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Link: https://lore.kernel.org/r/20230126151323.408156109@infradead.org

Signed-off-by: Waiman Long <longman@redhat.com>

include/linux/context_tracking.h

@@ -130,9 +130,36 @@ static __always_inline unsigned long ct_state_inc(int incby)
 	return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.state));
 }
 
+static __always_inline bool warn_rcu_enter(void)
+{
+	bool ret = false;
+
+	/*
+	 * Horrible hack to shut up recursive RCU isn't watching fail since
+	 * lots of the actual reporting also relies on RCU.
+	 */
+	preempt_disable_notrace();
+	if (rcu_dynticks_curr_cpu_in_eqs()) {
+		ret = true;
+		ct_state_inc(RCU_DYNTICKS_IDX);
+	}
+
+	return ret;
+}
+
+static __always_inline void warn_rcu_exit(bool rcu)
+{
+	if (rcu)
+		ct_state_inc(RCU_DYNTICKS_IDX);
+	preempt_enable_notrace();
+}
+
 #else
 static inline void ct_idle_enter(void) { }
 static inline void ct_idle_exit(void) { }
+
+static __always_inline bool warn_rcu_enter(void) { return false; }
+static __always_inline void warn_rcu_exit(bool rcu) { }
 #endif /* !CONFIG_CONTEXT_TRACKING_IDLE */
 
 #endif

kernel/locking/lockdep.c

@@ -55,6 +55,7 @@
 #include <linux/rcupdate.h>
 #include <linux/kprobes.h>
 #include <linux/lockdep.h>
+#include <linux/context_tracking.h>
 
 #include <asm/sections.h>
 
@@ -6525,6 +6526,7 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 {
 	struct task_struct *curr = current;
 	int dl = READ_ONCE(debug_locks);
+	bool rcu = warn_rcu_enter();
 
 	/* Note: the following can be executed concurrently, so be careful. */
 	pr_warn("\n");
@@ -6565,5 +6567,6 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 	lockdep_print_held_locks(curr);
 	pr_warn("\nstack backtrace:\n");
 	dump_stack();
+	warn_rcu_exit(rcu);
 }
 EXPORT_SYMBOL_GPL(lockdep_rcu_suspicious);

kernel/panic.c

@@ -32,6 +32,7 @@
 #include <linux/bug.h>
 #include <linux/ratelimit.h>
 #include <linux/debugfs.h>
+#include <linux/context_tracking.h>
 #include <asm/sections.h>
 
 #define PANIC_TIMER_STEP 100
@@ -642,6 +643,7 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 void warn_slowpath_fmt(const char *file, int line, unsigned taint,
 		       const char *fmt, ...)
 {
+	bool rcu = warn_rcu_enter();
 	struct warn_args args;
 
 	pr_warn(CUT_HERE);
@@ -656,11 +658,13 @@ void warn_slowpath_fmt(const char *file, int line, unsigned taint,
 	va_start(args.args, fmt);
 	__warn(file, line, __builtin_return_address(0), taint, NULL, &args);
 	va_end(args.args);
+	warn_rcu_exit(rcu);
 }
 EXPORT_SYMBOL(warn_slowpath_fmt);
 #else
 void __warn_printk(const char *fmt, ...)
 {
+	bool rcu = warn_rcu_enter();
 	va_list args;
 
 	pr_warn(CUT_HERE);
@@ -668,6 +672,7 @@ void __warn_printk(const char *fmt, ...)
 	va_start(args, fmt);
 	vprintk(fmt, args);
 	va_end(args);
+	warn_rcu_exit(rcu);
 }
 EXPORT_SYMBOL(__warn_printk);
 #endif

lib/bug.c

@@ -47,6 +47,7 @@
 #include <linux/sched.h>
 #include <linux/rculist.h>
 #include <linux/ftrace.h>
+#include <linux/context_tracking.h>
 
 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
 
@@ -153,7 +154,7 @@ struct bug_entry *find_bug(unsigned long bugaddr)
 	return module_find_bug(bugaddr);
 }
 
-enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
+static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
 {
 	struct bug_entry *bug;
 	const char *file;
@@ -209,6 +210,18 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 	return BUG_TRAP_TYPE_BUG;
 }
 
+enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
+{
+	enum bug_trap_type ret;
+	bool rcu = false;
+
+	rcu = warn_rcu_enter();
+	ret = __report_bug(bugaddr, regs);
+	warn_rcu_exit(rcu);
+
+	return ret;
+}
+
 static void clear_once_table(struct bug_entry *start, struct bug_entry *end)
 {
 	struct bug_entry *bug;