lockdep: Comment all warnings

Andrew requested I comment all the lockdep WARN()s to help other people
figure out wth is wrong..

Requested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1315301493.3191.9.camel@twins
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 147 insertions, 9 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 91d67ce3a8d5..c081fa967c8f 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -96,8 +96,13 @@ static int graph_lock(void)
 
 static inline int graph_unlock(void)
 {
-        if (debug_locks && !arch_spin_is_locked(&lockdep_lock))
+        if (debug_locks && !arch_spin_is_locked(&lockdep_lock)) {
+                /*
+                 * The lockdep graph lock isn't locked while we expect it to
+                 * be, we're confused now, bye!
+                 */
                 return DEBUG_LOCKS_WARN_ON(1);
+        }
 
         current->lockdep_recursion--;
         arch_spin_unlock(&lockdep_lock);
@@ -134,6 +139,9 @@ static struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
 static inline struct lock_class *hlock_class(struct held_lock *hlock)
 {
         if (!hlock->class_idx) {
+                /*
+                 * Someone passed in garbage, we give up.
+                 */
                 DEBUG_LOCKS_WARN_ON(1);
                 return NULL;
         }
@@ -687,6 +695,10 @@ look_up_lock_class(struct lockdep_map *lock, unsigned int subclass)
          */
         list_for_each_entry(class, hash_head, hash_entry) {
                 if (class->key == key) {
+                        /*
+                         * Huh! same key, different name? Did someone trample
+                         * on some memory? We're most confused.
+                         */
                         WARN_ON_ONCE(class->name != lock->name);
                         return class;
                 }
@@ -800,6 +812,10 @@ out_unlock_set:
         else if (subclass < NR_LOCKDEP_CACHING_CLASSES)
                 lock->class_cache[subclass] = class;
 
+        /*
+         * Hash collision, did we smoke some? We found a class with a matching
+         * hash but the subclass -- which is hashed in -- didn't match.
+         */
         if (DEBUG_LOCKS_WARN_ON(class->subclass != subclass))
                 return NULL;
 
@@ -926,7 +942,7 @@ static inline void mark_lock_accessed(struct lock_list *lock,
         unsigned long nr;
 
         nr = lock - list_entries;
-        WARN_ON(nr >= nr_list_entries);
+        WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
         lock->parent = parent;
         lock->class->dep_gen_id = lockdep_dependency_gen_id;
 }
@@ -936,7 +952,7 @@ static inline unsigned long lock_accessed(struct lock_list *lock)
         unsigned long nr;
 
         nr = lock - list_entries;
-        WARN_ON(nr >= nr_list_entries);
+        WARN_ON(nr >= nr_list_entries); /* Out-of-bounds, input fail */
         return lock->class->dep_gen_id == lockdep_dependency_gen_id;
 }
 
@@ -1196,6 +1212,9 @@ static noinline int print_bfs_bug(int ret)
         if (!debug_locks_off_graph_unlock())
                 return 0;
 
+        /*
+         * Breadth-first-search failed, graph got corrupted?
+         */
         WARN(1, "lockdep bfs error:%d\n", ret);
 
         return 0;
@@ -1944,6 +1963,11 @@ out_bug:
         if (!debug_locks_off_graph_unlock())
                 return 0;
 
+        /*
+         * Clearly we all shouldn't be here, but since we made it we
+         * can reliable say we messed up our state. See the above two
+         * gotos for reasons why we could possibly end up here.
+         */
         WARN_ON(1);
 
         return 0;
@@ -1975,6 +1999,11 @@ static inline int lookup_chain_cache(struct task_struct *curr,
         struct held_lock *hlock_curr, *hlock_next;
         int i, j;
 
+        /*
+         * We might need to take the graph lock, ensure we've got IRQs
+         * disabled to make this an IRQ-safe lock.. for recursion reasons
+         * lockdep won't complain about its own locking errors.
+         */
         if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                 return 0;
         /*
@@ -2126,6 +2155,10 @@ static void check_chain_key(struct task_struct *curr)
                 hlock = curr->held_locks + i;
                 if (chain_key != hlock->prev_chain_key) {
                         debug_locks_off();
+                        /*
+                         * We got mighty confused, our chain keys don't match
+                         * with what we expect, someone trample on our task state?
+                         */
                         WARN(1, "hm#1, depth: %u [%u], %016Lx != %016Lx\n",
                                 curr->lockdep_depth, i,
                                 (unsigned long long)chain_key,
@@ -2133,6 +2166,9 @@ static void check_chain_key(struct task_struct *curr)
                         return;
                 }
                 id = hlock->class_idx - 1;
+                /*
+                 * Whoops ran out of static storage again?
+                 */
                 if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
                         return;
 
@@ -2144,6 +2180,10 @@ static void check_chain_key(struct task_struct *curr)
         }
         if (chain_key != curr->curr_chain_key) {
                 debug_locks_off();
+                /*
+                 * More smoking hash instead of calculating it, damn see these
+                 * numbers float.. I bet that a pink elephant stepped on my memory.
+                 */
                 WARN(1, "hm#2, depth: %u [%u], %016Lx != %016Lx\n",
                         curr->lockdep_depth, i,
                         (unsigned long long)chain_key,
@@ -2525,12 +2565,24 @@ void trace_hardirqs_on_caller(unsigned long ip)
                 return;
         }
 
+        /*
+         * We're enabling irqs and according to our state above irqs weren't
+         * already enabled, yet we find the hardware thinks they are in fact
+         * enabled.. someone messed up their IRQ state tracing.
+         */
         if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                 return;
 
+        /*
+         * See the fine text that goes along with this variable definition.
+         */
         if (DEBUG_LOCKS_WARN_ON(unlikely(early_boot_irqs_disabled)))
                 return;
 
+        /*
+         * Can't allow enabling interrupts while in an interrupt handler,
+         * that's general bad form and such. Recursion, limited stack etc..
+         */
         if (DEBUG_LOCKS_WARN_ON(current->hardirq_context))
                 return;
 
@@ -2558,6 +2610,10 @@ void trace_hardirqs_off_caller(unsigned long ip)
         if (unlikely(!debug_locks || current->lockdep_recursion))
                 return;
 
+        /*
+         * So we're supposed to get called after you mask local IRQs, but for
+         * some reason the hardware doesn't quite think you did a proper job.
+         */
         if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                 return;
 
@@ -2590,6 +2646,10 @@ void trace_softirqs_on(unsigned long ip)
         if (unlikely(!debug_locks || current->lockdep_recursion))
                 return;
 
+        /*
+         * We fancy IRQs being disabled here, see softirq.c, avoids
+         * funny state and nesting things.
+         */
         if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                 return;
 
@@ -2626,6 +2686,9 @@ void trace_softirqs_off(unsigned long ip)
         if (unlikely(!debug_locks || current->lockdep_recursion))
                 return;
 
+        /*
+         * We fancy IRQs being disabled here, see softirq.c
+         */
         if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                 return;
 
@@ -2637,6 +2700,9 @@ void trace_softirqs_off(unsigned long ip)
                 curr->softirq_disable_ip = ip;
                 curr->softirq_disable_event = ++curr->irq_events;
                 debug_atomic_inc(softirqs_off_events);
+                /*
+                 * Whoops, we wanted softirqs off, so why aren't they?
+                 */
                 DEBUG_LOCKS_WARN_ON(!softirq_count());
         } else
                 debug_atomic_inc(redundant_softirqs_off);
@@ -2661,6 +2727,9 @@ static void __lockdep_trace_alloc(gfp_t gfp_mask, unsigned long flags)
         if (!(gfp_mask & __GFP_FS))
                 return;
 
+        /*
+         * Oi! Can't be having __GFP_FS allocations with IRQs disabled.
+         */
         if (DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags)))
                 return;
 
@@ -2773,13 +2842,13 @@ static int separate_irq_context(struct task_struct *curr,
         return 0;
 }
 
-#else
+#else /* defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) */
 
 static inline
 int mark_lock_irq(struct task_struct *curr, struct held_lock *this,
                 enum lock_usage_bit new_bit)
 {
-        WARN_ON(1);
+        WARN_ON(1); /* Impossible innit? when we don't have TRACE_IRQFLAG */
         return 1;
 }
 
@@ -2799,7 +2868,7 @@ void lockdep_trace_alloc(gfp_t gfp_mask)
 {
 }
 
-#endif
+#endif /* defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) */
 
 /*
  * Mark a lock with a usage bit, and validate the state transition:
@@ -2880,6 +2949,9 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
         lock->cpu = raw_smp_processor_id();
 #endif
 
+        /*
+         * Can't be having no nameless bastards around this place!
+         */
         if (DEBUG_LOCKS_WARN_ON(!name)) {
                 lock->name = "NULL";
                 return;
@@ -2887,6 +2959,9 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
 
         lock->name = name;
 
+        /*
+         * No key, no joy, we need to hash something.
+         */
         if (DEBUG_LOCKS_WARN_ON(!key))
                 return;
         /*
@@ -2894,6 +2969,9 @@ void lockdep_init_map(struct lockdep_map *lock, const char *name,
          */
         if (!static_obj(key)) {
                 printk("BUG: key %p not in .data!\n", key);
+                /*
+                 * What it says above ^^^^^, I suggest you read it.
+                 */
                 DEBUG_LOCKS_WARN_ON(1);
                 return;
         }
@@ -2932,6 +3010,11 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
         if (unlikely(!debug_locks))
                 return 0;
 
+        /*
+         * Lockdep should run with IRQs disabled, otherwise we could
+         * get an interrupt which would want to take locks, which would
+         * end up in lockdep and have you got a head-ache already?
+         */
         if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                 return 0;
 
@@ -2963,6 +3046,9 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
          * dependency checks are done)
          */
         depth = curr->lockdep_depth;
+        /*
+         * Ran out of static storage for our per-task lock stack again have we?
+         */
         if (DEBUG_LOCKS_WARN_ON(depth >= MAX_LOCK_DEPTH))
                 return 0;
 
@@ -2981,6 +3067,10 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
         }
 
         hlock = curr->held_locks + depth;
+        /*
+         * Plain impossible, we just registered it and checked it weren't no
+         * NULL like.. I bet this mushroom I ate was good!
+         */
         if (DEBUG_LOCKS_WARN_ON(!class))
                 return 0;
         hlock->class_idx = class_idx;
@@ -3015,11 +3105,17 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
          * the hash, not class->key.
          */
         id = class - lock_classes;
+        /*
+         * Whoops, we did it again.. ran straight out of our static allocation.
+         */
         if (DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
                 return 0;
 
         chain_key = curr->curr_chain_key;
         if (!depth) {
+                /*
+                 * How can we have a chain hash when we ain't got no keys?!
+                 */
                 if (DEBUG_LOCKS_WARN_ON(chain_key != 0))
                         return 0;
                 chain_head = 1;
@@ -3091,6 +3187,9 @@ static int check_unlock(struct task_struct *curr, struct lockdep_map *lock,
 {
         if (unlikely(!debug_locks))
                 return 0;
+        /*
+         * Lockdep should run with IRQs disabled, recursion, head-ache, etc..
+         */
         if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
                 return 0;
 
@@ -3120,6 +3219,11 @@ static int match_held_lock(struct held_lock *hlock, struct lockdep_map *lock)
                 if (!class)
                         return 0;
 
+                /*
+                 * References, but not a lock we're actually ref-counting?
+                 * State got messed up, follow the sites that change ->references
+                 * and try to make sense of it.
+                 */
                 if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock))
                         return 0;
 
@@ -3142,6 +3246,10 @@ __lock_set_class(struct lockdep_map *lock, const char *name,
         int i;
 
         depth = curr->lockdep_depth;
+        /*
+         * This function is about (re)setting the class of a held lock,
+         * yet we're not actually holding any locks. Naughty user!
+         */
         if (DEBUG_LOCKS_WARN_ON(!depth))
                 return 0;
 
@@ -3177,6 +3285,10 @@ found_it:
                         return 0;
         }
 
+        /*
+         * I took it apart and put it back together again, except now I have
+         * these 'spare' parts.. where shall I put them.
+         */
         if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth))
                 return 0;
         return 1;
@@ -3201,6 +3313,10 @@ lock_release_non_nested(struct task_struct *curr,
          * of held locks:
          */
         depth = curr->lockdep_depth;
+        /*
+         * So we're all set to release this lock.. wait what lock? We don't
+         * own any locks, you've been drinking again?
+         */
         if (DEBUG_LOCKS_WARN_ON(!depth))
                 return 0;
 
@@ -3253,6 +3369,10 @@ found_it:
                         return 0;
         }
 
+        /*
+         * We had N bottles of beer on the wall, we drank one, but now
+         * there's not N-1 bottles of beer left on the wall...
+         */
         if (DEBUG_LOCKS_WARN_ON(curr->lockdep_depth != depth - 1))
                 return 0;
         return 1;
@@ -3283,6 +3403,9 @@ static int lock_release_nested(struct task_struct *curr,
                 return lock_release_non_nested(curr, lock, ip);
         curr->lockdep_depth--;
 
+        /*
+         * No more locks, but somehow we've got hash left over, who left it?
+         */
         if (DEBUG_LOCKS_WARN_ON(!depth && (hlock->prev_chain_key != 0)))
                 return 0;
 
@@ -3365,10 +3488,13 @@ static void check_flags(unsigned long flags)
          * check if not in hardirq contexts:
          */
         if (!hardirq_count()) {
-                if (softirq_count())
+                if (softirq_count()) {
+                        /* like the above, but with softirqs */
                         DEBUG_LOCKS_WARN_ON(current->softirqs_enabled);
-                else
+                } else {
+                        /* lick the above, does it taste good? */
                         DEBUG_LOCKS_WARN_ON(!current->softirqs_enabled);
+                }
         }
 
         if (!debug_locks)
@@ -3506,6 +3632,10 @@ __lock_contended(struct lockdep_map *lock, unsigned long ip)
         int i, contention_point, contending_point;
 
         depth = curr->lockdep_depth;
+        /*
+         * Whee, we contended on this lock, except it seems we're not
+         * actually trying to acquire anything much at all..
+         */
         if (DEBUG_LOCKS_WARN_ON(!depth))
                 return;
 
@@ -3555,6 +3685,10 @@ __lock_acquired(struct lockdep_map *lock, unsigned long ip)
         int i, cpu;
 
         depth = curr->lockdep_depth;
+        /*
+         * Yay, we acquired ownership of this lock we didn't try to
+         * acquire, how the heck did that happen?
+         */
         if (DEBUG_LOCKS_WARN_ON(!depth))
                 return;
 
@@ -3759,8 +3893,12 @@ void lockdep_reset_lock(struct lockdep_map *lock)
                                 match |= class == lock->class_cache[j];
 
                         if (unlikely(match)) {
-                                if (debug_locks_off_graph_unlock())
+                                if (debug_locks_off_graph_unlock()) {
+                                        /*
+                                         * We all just reset everything, how did it match?
+                                         */
                                         WARN_ON(1);
+                                }
                                 goto out_restore;
                         }
                 }