svn commit: r320561 - head/sys/kern

[Mateusz Guzik]

Author: mjg
Date: Sun Jul  2 01:05:16 2017
New Revision: 320561
URL: https://svnweb.freebsd.org/changeset/base/320561

Log:
  rwlock: perform the typically false td_rw_rlocks check later
  
  Check if the lock is available first instead.
  
  MFC after:	1 week

Modified:
  head/sys/kern/kern_rwlock.c

Modified: head/sys/kern/kern_rwlock.c
==============================================================================
--- head/sys/kern/kern_rwlock.c	Sat Jul  1 23:39:49 2017	(r320560)
+++ head/sys/kern/kern_rwlock.c	Sun Jul  2 01:05:16 2017	(r320561)
@@ -372,9 +372,8 @@ _rw_wunlock_cookie(volatile uintptr_t *c, const char *
  * prioritizes writers before readers.
  */
 #define	RW_CAN_READ(td, _rw)						\
-    (((td)->td_rw_rlocks && (_rw) & RW_LOCK_READ) || ((_rw) &	\
-    (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) ==	\
-    RW_LOCK_READ)
+    (((_rw) & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) ==\
+    RW_LOCK_READ || ((td)->td_rw_rlocks && (_rw) & RW_LOCK_READ))
 
 static bool __always_inline
 __rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp,