Commit 5a5d7e9b authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230126151323.408156109@infradead.org
parent 393e2ea3

include/linux/context_tracking.h

+27 −0
Original line number Diff line number Diff line
@@ -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

+3 −0
Original line number Diff line number Diff line
@@ -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>
@@ -6555,6 +6556,7 @@ 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");
@@ -6595,5 +6597,6 @@ 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

+5 −0
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ 
#include <linux/ratelimit.h>

#include <linux/debugfs.h>

#include <linux/sysfs.h>

#include <linux/context_tracking.h>

#include <trace/events/error_report.h>

#include <asm/sections.h>
@@ -679,6 +680,7 @@ 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);
@@ -693,11 +695,13 @@ 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);
@@ -705,6 +709,7 @@ 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

+14 −1
Original line number Diff line number Diff line
@@ -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;