Commit 75dd602a authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent c2469756

include/linux/lockdep.h

+5 −3
Original line number Diff line number Diff line
@@ -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;

};

kernel/locking/lockdep.c

+23 −1
Original line number Diff line number Diff line
@@ -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();

kernel/locking/lockdep_proc.c

+2 −0
Original line number Diff line number Diff line
@@ -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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