svn commit: r304812 - head/sys/kern

[Konstantin Belousov]

Author: kib
Date: Thu Aug 25 19:15:02 2016
New Revision: 304812
URL: https://svnweb.freebsd.org/changeset/base/304812

Log:
  In both do_rw_wrlock() and do_rw_rdlock() after r304808, do not
  obliterate possible error from sleep with errors from
  umtxq_check_susp(), when looping to clear URWLOCK_{READ,WRITE}_WAITERS.
  
  Noted and reviewed by:	vangyzen
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/kern/kern_umtx.c

Modified: head/sys/kern/kern_umtx.c
==============================================================================
--- head/sys/kern/kern_umtx.c	Thu Aug 25 17:30:00 2016	(r304811)
+++ head/sys/kern/kern_umtx.c	Thu Aug 25 19:15:02 2016	(r304812)
@@ -2609,7 +2609,7 @@ do_rw_rdlock(struct thread *td, struct u
 	uint32_t flags, wrflags;
 	int32_t state, oldstate;
 	int32_t blocked_readers;
-	int error, rv;
+	int error, error1, rv;
 
 	uq = td->td_umtxq;
 	error = fueword32(&rwlock->rw_flags, &flags);
@@ -2758,9 +2758,12 @@ sleep:
 				if (oldstate == state)
 					break;
 				state = oldstate;
-				error = umtxq_check_susp(td);
-				if (error != 0)
+				error1 = umtxq_check_susp(td);
+				if (error1 != 0) {
+					if (error == 0)
+						error = error1;
 					break;
+				}
 			}
 		}
 
@@ -2783,7 +2786,7 @@ do_rw_wrlock(struct thread *td, struct u
 	int32_t state, oldstate;
 	int32_t blocked_writers;
 	int32_t blocked_readers;
-	int error, rv;
+	int error, error1, rv;
 
 	uq = td->td_umtxq;
 	error = fueword32(&rwlock->rw_flags, &flags);
@@ -2929,14 +2932,17 @@ sleep:
 				if (oldstate == state)
 					break;
 				state = oldstate;
-				error = umtxq_check_susp(td);
+				error1 = umtxq_check_susp(td);
 				/*
 				 * We are leaving the URWLOCK_WRITE_WAITERS
 				 * behind, but this should not harm the
 				 * correctness.
 				 */
-				if (error != 0)
+				if (error1 != 0) {
+					if (error == 0)
+						error = error1;
 					break;
+				}
 			}
 			rv = fueword32(&rwlock->rw_blocked_readers,
 			    &blocked_readers);