Remove brain damaged code in witness_lock(). We could have easily

just used PCPU_GET(spinlocks) w/o needing the w_mtx held.  It is more
correct to just check td_critnest now though.

1 files changed, 3 insertions, 16 deletions

diff --git a/sys/kern/subr_witness.c b/sys/kern/subr_witness.c
index 1c70d86..b798579 100644
--- a/sys/kern/subr_witness.c
+++ b/sys/kern/subr_witness.c
@@ -475,26 +475,13 @@ witness_lock(struct lock_object *lock, int flags, const char *file, int line)
 	class = lock->lo_class;
 	td = curthread;
 
-	/*
-	 * We have to hold a spinlock to keep lock_list valid across the check
-	 * in the LC_SLEEPLOCK case.  In the LC_SPINLOCK case, it is already
-	 * protected by the spinlock we are currently performing the witness
-	 * checks on, so it is ok to release the lock after performing this
-	 * check.  All we have to protect is the LC_SLEEPLOCK case when no
-	 * spinlocks are held as we may get preempted during this check and
-	 * lock_list could end up pointing to some other CPU's spinlock list.
-	 */
-	mtx_lock_spin(&w_mtx);
-	lock_list = PCPU_PTR(spinlocks);
 	if (class->lc_flags & LC_SLEEPLOCK) {
-		if (*lock_list != NULL && (flags & LOP_TRYLOCK) == 0) {
-			mtx_unlock_spin(&w_mtx);
+		if (td->td_critnest != 0 && (flags & LOP_TRYLOCK) == 0)
 			panic("blockable sleep lock (%s) %s @ %s:%d",
 			    class->lc_name, lock->lo_name, file, line);
-		}
 		lock_list = &td->td_sleeplocks;
-	}
-	mtx_unlock_spin(&w_mtx);
+	} else
+		lock_list = PCPU_PTR(spinlocks);
 
 	/*
 	 * Try locks do not block if they fail to acquire the lock, thus