Commit-ID:  75dd602a5198a6e5f75534db52b6e6fbaabb33d1
Gitweb:     http://git.kernel.org/tip/75dd602a5198a6e5f75534db52b6e6fbaabb33d1
Author:     Peter Zijlstra <pet...@infradead.org>
AuthorDate: Wed, 30 Mar 2016 11:36:59 +0200
Committer:  Ingo Molnar <mi...@kernel.org>
CommitDate: Sat, 23 Apr 2016 13:53:03 +0200

lockdep: Fix lock_chain::base size

lock_chain::base is used to store an index into the chain_hlocks[]
array, however that array contains more elements than can be indexed
using the u16.

Change the lock_chain structure to use a bitfield to encode the data
it needs and add BUILD_BUG_ON() assertions to check the fields are
wide enough.

Also, for DEBUG_LOCKDEP, assert that we don't run out of elements of
that array; as that would wreck the collision detectoring.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: Alfredo Alvarez Fernandez <alfredoalvarezfernan...@gmail.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Sedat Dilek <sedat.di...@gmail.com>
Cc: Theodore Ts'o <ty...@mit.edu>
Cc: Thomas Gleixner <t...@linutronix.de>
Link: 
http://lkml.kernel.org/r/20160330093659.gs3...@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
 include/linux/lockdep.h       |  8 +++++---
 kernel/locking/lockdep.c      | 24 +++++++++++++++++++++++-
 kernel/locking/lockdep_proc.c |  2 ++
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index d026b19..d10ef06 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -196,9 +196,11 @@ struct lock_list {
  * We record lock dependency chains, so that we can cache them:
  */
 struct lock_chain {
-       u8                              irq_context;
-       u8                              depth;
-       u16                             base;
+       /* see BUILD_BUG_ON()s in lookup_chain_cache() */
+       unsigned int                    irq_context :  2,
+                                       depth       :  6,
+                                       base        : 24;
+       /* 4 byte hole */
        struct hlist_node               entry;
        u64                             chain_key;
 };
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index beb06f6..78c1c0e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2176,15 +2176,37 @@ cache_hit:
        chain->irq_context = hlock->irq_context;
        i = get_first_held_lock(curr, hlock);
        chain->depth = curr->lockdep_depth + 1 - i;
+
+       BUILD_BUG_ON((1UL << 24) <= ARRAY_SIZE(chain_hlocks));
+       BUILD_BUG_ON((1UL << 6)  <= ARRAY_SIZE(curr->held_locks));
+       BUILD_BUG_ON((1UL << 8*sizeof(chain_hlocks[0])) <= 
ARRAY_SIZE(lock_classes));
+
        if (likely(nr_chain_hlocks + chain->depth <= MAX_LOCKDEP_CHAIN_HLOCKS)) 
{
                chain->base = nr_chain_hlocks;
-               nr_chain_hlocks += chain->depth;
                for (j = 0; j < chain->depth - 1; j++, i++) {
                        int lock_id = curr->held_locks[i].class_idx - 1;
                        chain_hlocks[chain->base + j] = lock_id;
                }
                chain_hlocks[chain->base + j] = class - lock_classes;
        }
+
+       if (nr_chain_hlocks < MAX_LOCKDEP_CHAIN_HLOCKS)
+               nr_chain_hlocks += chain->depth;
+
+#ifdef CONFIG_DEBUG_LOCKDEP
+       /*
+        * Important for check_no_collision().
+        */
+       if (unlikely(nr_chain_hlocks > MAX_LOCKDEP_CHAIN_HLOCKS)) {
+               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();
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index dbb61a3..a0f61ef 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -141,6 +141,8 @@ static int lc_show(struct seq_file *m, void *v)
        int i;
 
        if (v == SEQ_START_TOKEN) {
+               if (nr_chain_hlocks > MAX_LOCKDEP_CHAIN_HLOCKS)
+                       seq_printf(m, "(buggered) ");
                seq_printf(m, "all lock chains:\n");
                return 0;
        }

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