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lockdep: Print a nicer description for normal deadlocks 

The lockdep output can be pretty cryptic, having nicer output
can save a lot of head scratching. When a normal deadlock
scenario is detected by lockdep (lock A -> lock B and there
exists a place where lock B -> lock A) we now get the following
new output:

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(lockB);
                               lock(lockA);
                               lock(lockB);
  lock(lockA);

 *** DEADLOCK ***

On cases where there's a deeper chair, it shows the partial
chain that can cause the issue:

Chain exists of:
  lockC --> lockA --> lockB

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(lockB);
                               lock(lockA);
                               lock(lockB);
  lock(lockC);

 *** 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/20110421014259.380621789@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Steven Rostedt 2011-04-20 21:41:55 -04:00 committed by Ingo Molnar
parent 3003eba313
commit f4185812aa
1 changed files with 55 additions and 0 deletions
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55
kernel/lockdep.c
View File

@ -1065,6 +1065,56 @@ print_circular_bug_entry(struct lock_list *target, int depth)
return 0;
}
static void
print_circular_lock_scenario(struct held_lock *src,
struct held_lock *tgt,
struct lock_list *prt)
{
struct lock_class *source = hlock_class(src);
struct lock_class *target = hlock_class(tgt);
struct lock_class *parent = prt->class;
/*
* A direct locking problem where unsafe_class lock is taken
* directly by safe_class lock, then all we need to show
* is the deadlock scenario, as it is obvious that the
* unsafe lock is taken under the safe lock.
*
* But if there is a chain instead, where the safe lock takes
* an intermediate lock (middle_class) where this lock is
* not the same as the safe lock, then the lock chain is
* used to describe the problem. Otherwise we would need
* to show a different CPU case for each link in the chain
* from the safe_class lock to the unsafe_class lock.
*/
if (parent != source) {
printk("Chain exists of:\n ");
__print_lock_name(source);
printk(" --> ");
__print_lock_name(parent);
printk(" --> ");
__print_lock_name(target);
printk("\n\n");
}
printk(" Possible unsafe locking scenario:\n\n");
printk(" CPU0 CPU1\n");
printk(" ---- ----\n");
printk(" lock(");
__print_lock_name(target);
printk(");\n");
printk(" lock(");
__print_lock_name(parent);
printk(");\n");
printk(" lock(");
__print_lock_name(target);
printk(");\n");
printk(" lock(");
__print_lock_name(source);
printk(");\n");
printk("\n *** DEADLOCK ***\n\n");
}
/*
* When a circular dependency is detected, print the
* header first:
@ -1108,6 +1158,7 @@ static noinline int print_circular_bug(struct lock_list *this,
{
struct task_struct *curr = current;
struct lock_list *parent;
struct lock_list *first_parent;
int depth;
if (!debug_locks_off_graph_unlock() || debug_locks_silent)
@ -1121,6 +1172,7 @@ static noinline int print_circular_bug(struct lock_list *this,
print_circular_bug_header(target, depth, check_src, check_tgt);
parent = get_lock_parent(target);
first_parent = parent;
while (parent) {
print_circular_bug_entry(parent, --depth);
@ -1128,6 +1180,9 @@ static noinline int print_circular_bug(struct lock_list *this,
}
printk("\nother info that might help us debug this:\n\n");
print_circular_lock_scenario(check_src, check_tgt,
first_parent);
lockdep_print_held_locks(curr);
printk("\nstack backtrace:\n");