[tip:locking/urgent] lockdep: Fix lock_chain::base size

tip-bot for Peter Zijlstra
2016-04-23T12:55:06Z

Commit-ID: 75dd602a5198a6e5f75534db52b6e6fbaabb33d1
Gitweb: http://git.kernel.org/tip/75dd602a5198a6e5f75534db52b6e6fbaabb33d1
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 30 Mar 2016 11:36:59 +0200
Committer: Ingo Molnar <mingo@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) <peterz@infradead.org>
Cc: Alfredo Alvarez Fernandez <alfredoalvarezfernandez@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160330093659.GS3408@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@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;
}