Commit-ID:  49347a986ab45eb1dafbf25170647c890f8ff192
Gitweb:     http://git.kernel.org/tip/49347a986ab45eb1dafbf25170647c890f8ff192
Author:     Byungchul Park <byungchul.p...@lge.com>
AuthorDate: Mon, 7 Aug 2017 16:12:49 +0900
Committer:  Ingo Molnar <mi...@kernel.org>
CommitDate: Thu, 10 Aug 2017 12:29:05 +0200

locking/lockdep: Add a function building a chain between two classes

Crossrelease needs to build a chain between two classes regardless of
their contexts. However, add_chain_cache() cannot be used for that
purpose since it assumes that it's called in the acquisition context
of the hlock. So this patch introduces a new function doing it.

Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: a...@linux-foundation.org
Cc: boqun.f...@gmail.com
Cc: kernel-t...@lge.com
Cc: kir...@shutemov.name
Cc: npig...@gmail.com
Cc: wal...@google.com
Cc: wi...@infradead.org
Link: 
http://lkml.kernel.org/r/1502089981-21272-3-git-send-email-byungchul.p...@lge.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
 kernel/locking/lockdep.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e029f2f..bdf6b31 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2151,6 +2151,76 @@ static int check_no_collision(struct task_struct *curr,
 }
 
 /*
+ * This is for building a chain between just two different classes,
+ * instead of adding a new hlock upon current, which is done by
+ * add_chain_cache().
+ *
+ * This can be called in any context with two classes, while
+ * add_chain_cache() must be done within the lock owener's context
+ * since it uses hlock which might be racy in another context.
+ */
+static inline int add_chain_cache_classes(unsigned int prev,
+                                         unsigned int next,
+                                         unsigned int irq_context,
+                                         u64 chain_key)
+{
+       struct hlist_head *hash_head = chainhashentry(chain_key);
+       struct lock_chain *chain;
+
+       /*
+        * Allocate a new chain entry from the static array, and add
+        * it to the hash:
+        */
+
+       /*
+        * 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;
+
+       if (unlikely(nr_lock_chains >= MAX_LOCKDEP_CHAINS)) {
+               if (!debug_locks_off_graph_unlock())
+                       return 0;
+
+               print_lockdep_off("BUG: MAX_LOCKDEP_CHAINS too low!");
+               dump_stack();
+               return 0;
+       }
+
+       chain = lock_chains + nr_lock_chains++;
+       chain->chain_key = chain_key;
+       chain->irq_context = irq_context;
+       chain->depth = 2;
+       if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) 
{
+               chain->base = nr_chain_hlocks;
+               nr_chain_hlocks += chain->depth;
+               chain_hlocks[chain->base] = prev - 1;
+               chain_hlocks[chain->base + 1] = next -1;
+       }
+#ifdef CONFIG_DEBUG_LOCKDEP
+       /*
+        * Important for check_no_collision().
+        */
+       else {
+               if (!debug_locks_off_graph_unlock())
+                       return 0;
+
+               print_lockdep_off("BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!");
+               dump_stack();
+               return 0;
+       }
+#endif
+
+       hlist_add_head_rcu(&chain->entry, hash_head);
+       debug_atomic_inc(chain_lookup_misses);
+       inc_chains();
+
+       return 1;
+}
+
+/*
  * Adds a dependency chain into chain hashtable. And must be called with
  * graph_lock held.
  *

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