locking/lockdep: Reduce space occupied by stack traces

Although commit 669de8bda87b ("kernel/workqueue: Use dynamic lockdep keys
for workqueues") unregisters dynamic lockdep keys when a workqueue is
destroyed, a side effect of that commit is that all stack traces
associated with the lockdep key are leaked when a workqueue is destroyed.
Fix this by storing each unique stack trace once. Other changes in this
patch are:

- Use NULL instead of { .nr_entries = 0 } to represent 'no trace'.
- Store a pointer to a stack trace in struct lock_class and struct
  lock_list instead of storing 'nr_entries' and 'offset'.

This patch avoids that the following program triggers the "BUG:
MAX_STACK_TRACE_ENTRIES too low!" complaint:

	#include <fcntl.h>
	#include <unistd.h>

	int main()
	{
		for (;;) {
			int fd = open("/dev/infiniband/rdma_cm", O_RDWR);
			close(fd);
		}
	}

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reported-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <longman@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yuyang Du <duyuyang@gmail.com>
Link: https://lkml.kernel.org/r/20190722182443.216015-4-bvanassche@acm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 2e518369add4..93a008bf77db 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -92,6 +92,7 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
 #define MAX_LOCKDEP_ENTRIES	16384UL
 #define MAX_LOCKDEP_CHAINS_BITS	15
 #define MAX_STACK_TRACE_ENTRIES	262144UL
+#define STACK_TRACE_HASH_SIZE	8192
 #else
 #define MAX_LOCKDEP_ENTRIES	32768UL
 
@@ -102,6 +103,7 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ =
  * addresses. Protected by the hash_lock.
  */
 #define MAX_STACK_TRACE_ENTRIES	524288UL
+#define STACK_TRACE_HASH_SIZE	16384
 #endif
 
 #define MAX_LOCKDEP_CHAINS	(1UL << MAX_LOCKDEP_CHAINS_BITS)