lockdep: Print a nicer description for simple irq lock inversions

Lockdep output can be pretty cryptic, having nicer output
can save a lot of head scratching. When a simple irq inversion
scenario is detected by lockdep (lock A taken in interrupt
context but also in thread context without disabling interrupts)
we now get the following (hopefully more informative) output:

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(lockA);
  <Interrupt>
    lock(lockA);

 *** DEADLOCK ***

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014300.436140880@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 270cfa405d3935ed478e663b16c2075ff1a7a109..27c609f3eae568ccbb2b26f0a8c0e9e0c49eae13 100644 (file)
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -2158,6 +2158,24 @@ static void check_chain_key(struct task_struct *curr)
 #endif
 }
 
+static void
+print_usage_bug_scenario(struct held_lock *lock)
+{
+       struct lock_class *class = hlock_class(lock);
+
+       printk(" Possible unsafe locking scenario:\n\n");
+       printk("       CPU0\n");
+       printk("       ----\n");
+       printk("  lock(");
+       __print_lock_name(class);
+       printk(");\n");
+       printk("  <Interrupt>\n");
+       printk("    lock(");
+       __print_lock_name(class);
+       printk(");\n");
+       printk("\n *** DEADLOCK ***\n\n");
+}
+
 static int
 print_usage_bug(struct task_struct *curr, struct held_lock *this,
                enum lock_usage_bit prev_bit, enum lock_usage_bit new_bit)
@@ -2186,6 +2204,8 @@ print_usage_bug(struct task_struct *curr, struct held_lock *this,
 
        print_irqtrace_events(curr);
        printk("\nother info that might help us debug this:\n");
+       print_usage_bug_scenario(this);
+
        lockdep_print_held_locks(curr);
 
        printk("\nstack backtrace:\n");