svn commit: r287833 - head/sys/kern

[John Baldwin]

Author: jhb
Date: Tue Sep 15 22:16:21 2015
New Revision: 287833
URL: https://svnweb.freebsd.org/changeset/base/287833

Log:
  Threads holding a read lock of a sleepable rm lock are not permitted
  to sleep.  The rmlock implementation enforces this by disabling
  sleeping when a read lock is acquired. To simplify the implementation,
  sleeping is disabled for most of the duration of rm_rlock.  However,
  it doesn't need to be disabled until the lock is acquired.  If a
  sleepable rm lock is contested, then rm_rlock may need to acquire the
  backing sx lock.  This tripped the overly-broad assertion.  Fix by
  relaxing the assertion around the call to sx_xlock().
  
  Reported by:	mjg
  Reviewed by:	kib, mjg
  MFC after:	1 week
  Differential Revision:	https://reviews.freebsd.org/D3324

Modified:
  head/sys/kern/kern_rmlock.c

Modified: head/sys/kern/kern_rmlock.c
==============================================================================
--- head/sys/kern/kern_rmlock.c	Tue Sep 15 21:16:45 2015	(r287832)
+++ head/sys/kern/kern_rmlock.c	Tue Sep 15 22:16:21 2015	(r287833)
@@ -407,9 +407,11 @@ _rm_rlock_hard(struct rmlock *rm, struct
 				return (0);
 		}
 	} else {
-		if (rm->lock_object.lo_flags & LO_SLEEPABLE)
+		if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
+			THREAD_SLEEPING_OK();
 			sx_xlock(&rm->rm_lock_sx);
-		else
+			THREAD_NO_SLEEPING();
+		} else
 			mtx_lock(&rm->rm_lock_mtx);
 	}