nothing uses it. the few things that did use it were too tricky, so i'm
not keen to leave it around for people to cause confusion with in the
future.

ok?

Index: share/man/man9/rwlock.9
===================================================================
RCS file: /cvs/src/share/man/man9/rwlock.9,v
diff -u -p -r1.27 rwlock.9
--- share/man/man9/rwlock.9	29 Jan 2025 15:10:35 -0000	1.27
+++ share/man/man9/rwlock.9	17 May 2025 07:38:35 -0000
@@ -149,10 +149,6 @@ When waiting for a lock, allow signals t
 Do not wait for busy locks, fail with
 .Dv EBUSY
 instead.
-.It Dv RW_SLEEPFAIL
-Wait for busy locks, but do not obtain them, fail with
-.Dv EAGAIN
-instead.
 .It Dv RW_DUPOK
 Prevents
 .Xr witness 4 ,
Index: sys/sys/rwlock.h
===================================================================
RCS file: /cvs/src/sys/sys/rwlock.h,v
diff -u -p -r1.32 rwlock.h
--- sys/sys/rwlock.h	29 Jan 2025 15:10:09 -0000	1.32
+++ sys/sys/rwlock.h	17 May 2025 07:38:35 -0000
@@ -114,7 +114,6 @@ struct rwlock {
 #define RW_OPMASK		0x0007UL
 
 #define RW_INTR			0x0010UL /* interruptible sleep */
-#define RW_SLEEPFAIL		0x0020UL /* fail if we slept for the lock */
 #define RW_NOSLEEP		0x0040UL /* don't wait for the lock */
 #define RW_RECURSEFAIL		0x0080UL /* Fail on recursion for RRW locks. */
 #define RW_DUPOK		0x0100UL /* Permit duplicate lock */
Index: sys/kern/kern_rwlock.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_rwlock.c,v
diff -u -p -r1.55 kern_rwlock.c
--- sys/kern/kern_rwlock.c	29 Jan 2025 15:10:09 -0000	1.55
+++ sys/kern/kern_rwlock.c	17 May 2025 07:38:35 -0000
@@ -302,11 +302,6 @@ rw_do_enter_write(struct rwlock *rwl, in
 			rw_dec(&rwl->rwl_waiters);
 			return (error);
 		}
-		if (ISSET(flags, RW_SLEEPFAIL)) {
-			rw_dec(&rwl->rwl_waiters);
-			rw_exited(rwl);
-			return (EAGAIN);
-		}
 
 		owner = rw_cas(&rwl->rwl_owner, 0, self);
 	} while (owner != 0);
@@ -392,11 +387,9 @@ rw_do_enter_read(struct rwlock *rwl, int
 			db_enter();
 		}
 #endif
-		if (ISSET(flags, RW_INTR) && (error != 0))
-			goto fail;
-		if (ISSET(flags, RW_SLEEPFAIL)) {
-			error = EAGAIN;
-			goto fail;
+		if (ISSET(flags, RW_INTR) && (error != 0)) {
+			rw_dec(&rwl->rwl_readers);
+			return (error);
 		}
 	} while (!rw_read_incr(rwl, 0));
 	rw_dec(&rwl->rwl_readers);
@@ -406,9 +399,6 @@ locked:
 	WITNESS_LOCK(&rwl->rwl_lock_obj, lop_flags);
 
 	return (0);
-fail:
-	rw_dec(&rwl->rwl_readers);
-	return (error);
 }
 
 static int