lockdep: add comments to mark_lock_irq()
Peter Zijlstra [Tue, 27 Jan 2009 13:53:50 +0000 (14:53 +0100)]
re-add some of the comments that got lost in the refactoring.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/lockdep.c

index f40d916..02e6e06 100644 (file)
@@ -2054,6 +2054,9 @@ static int exclusive_bit(int new_bit)
        int state = new_bit & ~3;
        int dir = new_bit & 2;
 
+       /*
+        * keep state, bit flip the direction and strip read.
+        */
        return state | (dir ^ 2);
 }
 
@@ -2070,22 +2073,42 @@ mark_lock_irq(struct task_struct *curr, struct held_lock *this, int new_bit)
        int read = new_bit & 1;
        int dir = new_bit & 2;
 
+       /*
+        * mark USED_IN has to look forwards -- to ensure no dependency
+        * has ENABLED state, which would allow recursion deadlocks.
+        *
+        * mark ENABLED has to look backwards -- to ensure no dependee
+        * has USED_IN state, which, again, would allow  recursion deadlocks.
+        */
        check_usage_f usage = dir ?
                check_usage_backwards : check_usage_forwards;
 
+       /*
+        * Validate that this particular lock does not have conflicting
+        * usage states.
+        */
        if (!valid_state(curr, this, new_bit, excl_bit))
                return 0;
 
-       if (!read && !valid_state(curr, this, new_bit, excl_bit + 1))
-               return 0;
-
-       if ((!read || (!dir || STRICT_READ_CHECKS)) &&
+       /*
+        * Validate that the lock dependencies don't have conflicting usage
+        * states.
+        */
+       if ((!read || !dir || STRICT_READ_CHECKS) &&
                        !usage(curr, this, excl_bit, name))
                return 0;
 
-       if ((!read && STRICT_READ_CHECKS) &&
-                       !usage(curr, this, excl_bit + 1, rname))
-               return 0;
+       /*
+        * Check for read in write conflicts
+        */
+       if (!read) {
+               if (!valid_state(curr, this, new_bit, excl_bit + 1))
+                       return 0;
+
+               if (STRICT_READ_CHECKS &&
+                               !usage(curr, this, excl_bit + 1, rname))
+                       return 0;
+       }
 
        if (state_verbose(new_bit, hlock_class(this)))
                return 2;