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authorSteven Rostedt <srostedt@redhat.com>2011-04-20 21:41:55 -0400
committerIngo Molnar <mingo@elte.hu>2011-04-22 11:06:57 +0200
commitf4185812aa046ecb97e8817e10148cacdd7a6baa (patch)
treea17a417d13586554f452df9fd251165c4d714a97 /kernel/lockdep.c
parent3003eba313dd0e0502dd71548c36fe7c19801ce5 (diff)
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>
Diffstat (limited to 'kernel/lockdep.c')
-rw-r--r--kernel/lockdep.c55
1 files changed, 55 insertions, 0 deletions
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 7b2ffeedceb..73cebd7aa71 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -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");