Q: lockdep_assert_held_read() after downgrade_write()
From: J. R. Okajima
Date: Mon Jan 30 2017 - 16:27:13 EST
Peter Zijlstra,
May I ask you a question?
v4.10-rc1 got a commit
f831948 2016-11-30 locking/lockdep: Provide a type check for lock_is_held
I've tested a little and lockdep splat a stack trace.
{
DECLARE_RWSEM(rw);
static struct lock_class_key key;
lockdep_set_class(&rw, &key);
down_read(&rw);
lockdep_assert_held_read(&rw);
up_read(&rw);
down_write(&rw);
lockdep_assert_held_exclusive(&rw);
up_write(&rw);
downgrade_write(&rw);
lockdep_assert_held_read(&rw); <-- here
up_read(&rw);
}
I was expecting that lockdep_assert_held_read() splat nothing after
downgrade_write(). Is this warning an intentional behaviour?
Also the final up_read() gives me a warning too. It is produced at
lockdep.c:3514:lock_release(): DEBUG_LOCKS_WARN_ON(depth <= 0)
As an additional information, I increased some lockdep constants.
Do you think this is related?
include/linux/lockdep.h
+#define MAX_LOCKDEP_SUBCLASSES (8UL + 4)
+#define MAX_LOCKDEP_KEYS_BITS (13 + 3)
kernel/locking/lockdep_internals.h
+#define MAX_LOCKDEP_ENTRIES (32768UL << 5)
+#define MAX_LOCKDEP_CHAINS_BITS (16 + 5)
+#define MAX_STACK_TRACE_ENTRIES (524288UL << 5)
J. R. Okajima