Fix a potential LOR with sx_sleep() and cv_wait() with sx locks by

1) adding the thread to the sleepq via sleepq_add() before dropping the
lock, and 2) dropping the sleepq lock around calls to lc_unlock() for
sleepable locks (i.e. locks that use sleepq's in their implementation).

1 files changed, 7 insertions, 1 deletions

diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index 6e23d0d..d61dddf 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -182,7 +182,7 @@ _sleep(ident, lock, priority, wmesg, timo)
 	    td->td_tid, p->p_pid, p->p_comm, wmesg, ident);
 
 	DROP_GIANT();
-	if (lock != NULL) {
+	if (lock != NULL && !(class->lc_flags & LC_SLEEPABLE)) {
 		WITNESS_SAVE(lock, lock_witness);
 		lock_state = class->lc_unlock(lock);
 	} else
@@ -201,6 +201,12 @@ _sleep(ident, lock, priority, wmesg, timo)
 	sleepq_add(ident, ident == &lbolt ? NULL : lock, wmesg, flags, 0);
 	if (timo)
 		sleepq_set_timeout(ident, timo);
+	if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
+		sleepq_release(ident);
+		WITNESS_SAVE(lock, lock_witness);
+		lock_state = class->lc_unlock(lock);
+		sleepq_lock(ident);
+	}
 
 	/*
 	 * Adjust this thread's priority, if necessary.