linux-kernel - Re: Problem with WARN_ON in mutex

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Date:   Fri, 6 Dec 2019 13:32:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: Problem with WARN_ON in mutex_trylock() and rxrpc

On Thu, Dec 05, 2019 at 02:22:12PM +0100, Peter Zijlstra wrote:

> At the very least I'm going to do a lockdep patch that verifies the lock
> stack is 'empty' for the current irq_context when it changes.

Something like the below..

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 21619c92c377..c0a314dc9969 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -21,11 +21,13 @@
   extern void trace_softirqs_off(unsigned long ip);
   extern void lockdep_hardirqs_on(unsigned long ip);
   extern void lockdep_hardirqs_off(unsigned long ip);
+  extern void lockdep_leave_irq_context(void);
 #else
   static inline void trace_softirqs_on(unsigned long ip) { }
   static inline void trace_softirqs_off(unsigned long ip) { }
   static inline void lockdep_hardirqs_on(unsigned long ip) { }
   static inline void lockdep_hardirqs_off(unsigned long ip) { }
+  static inline void lockdep_leave_irq_context(void) { }
 #endif
 
 #ifdef CONFIG_TRACE_IRQFLAGS
@@ -41,6 +43,8 @@ do {						\
 } while (0)
 # define trace_hardirq_exit()			\
 do {						\
+	if (current->hardirq_context == 1)	\
+		lockdep_leave_irq_context();	\
 	current->hardirq_context--;		\
 } while (0)
 # define lockdep_softirq_enter()		\
@@ -49,6 +53,8 @@ do {						\
 } while (0)
 # define lockdep_softirq_exit()			\
 do {						\
+	if (current->softirq_context == 1)	\
+		lockdep_leave_irq_context();	\
 	current->softirq_context--;		\
 } while (0)
 #else
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 32282e7112d3..5c1102967927 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3600,6 +3600,43 @@ static inline unsigned int task_irq_context(struct task_struct *task)
 	return 2 * !!task->hardirq_context + !!task->softirq_context;
 }
 
+/*
+ * Validate the current irqcontext holds no locks.
+ */
+void lockdep_leave_irq_context(void)
+{
+	struct task_struct *curr = current;
+	unsigned int irq_context = task_irq_context(curr);
+	int depth = curr->lockdep_depth;
+	struct held_lock *hlock;
+
+	if (unlikely(!debug_locks || curr->lockdep_recursion))
+		return;
+
+	if (!depth)
+		return;
+
+	if (curr->held_locks[depth-1].irq_context != irq_context)
+		return;
+
+	pr_warn("\n");
+	pr_warn("========================================================\n");
+	pr_warn("WARNING: Leaving (soft/hard) IRQ context with locks held\n");
+	print_kernel_ident();
+	pr_warn("--------------------------------------------------------\n");
+
+	for (; depth; depth--) {
+		hlock = curr->held_locks + depth - 1;
+		if (hlock->irq_context != irq_context)
+			break;
+		print_lock(hlock);
+	}
+
+	pr_warn("\nstack backtrace:\n");
+	dump_stack();
+}
+NOKPROBE_SYMBOL(lockdep_leave_irq_context);
+
 static int separate_irq_context(struct task_struct *curr,
 		struct held_lock *hlock)
 {