lockdep: add comments to mark_lock_irq()

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>

1 files changed, 30 insertions, 7 deletions

diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index f40d916c191c..02e6e066d563 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -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;