Micro optimise _callout_stop_safe() by removing dead code.

The CS_DRAIN flag cannot be set at the same time like the async-drain function
pointer is set. These are orthogonal features. Assert this at the beginning
of the function.

Before:
        if (flags & CS_DRAIN) {
                /* FALLTHROUGH */
        } else if (xxx) {
                return yyy;
        }
        if (drain) {
                zzz = drain;
        }
After:
        if (flags & CS_DRAIN) {
                /* FALLTHROUGH */
        } else if (xxx) {
                return yyy;
        } else {
                if (drain) {
                        zzz = drain;
                }
        }

Reviewed by:	markj@
Tested by:	callout_test
Differential Revision:	https://reviews.freebsd.org/D26285
MFC after:	1 week
Sponsored by:	Mellanox Technologies // NVIDIA Networking

1 files changed, 9 insertions, 5 deletions

diff --git a/sys/kern/kern_timeout.c b/sys/kern/kern_timeout.c
index f804e279ec8b..760491d8c216 100644
--- a/sys/kern/kern_timeout.c
+++ b/sys/kern/kern_timeout.c
@@ -1075,6 +1075,9 @@ _callout_stop_safe(struct callout *c, int flags, callout_func_t *drain)
 		WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, c->c_lock,
 		    "calling %s", __func__);
 
+	KASSERT((flags & CS_DRAIN) == 0 || drain == NULL,
+	    ("Cannot set drain callback and CS_DRAIN flag at the same time"));
+
 	/*
 	 * Some old subsystems don't hold Giant while running a callout_stop(),
 	 * so just discard this check for the moment.
@@ -1270,11 +1273,12 @@ again:
 			}
 			CC_UNLOCK(cc);
 			return ((flags & CS_EXECUTING) != 0);
-		}
-		CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
-		    c, c->c_func, c->c_arg);
-		if (drain) {
-			cc_exec_drain(cc, direct) = drain;
+		} else {
+			CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
+			    c, c->c_func, c->c_arg);
+			if (drain) {
+				cc_exec_drain(cc, direct) = drain;
+			}
 		}
 		KASSERT(!sq_locked, ("sleepqueue chain still locked"));
 		cancelled = ((flags & CS_EXECUTING) != 0);