Use a name instead of a magic number for kern_yield(9) when the priority

should not change.  Fetch the td_user_pri under the thread lock.  This
is probably not necessary but a magic number also seems preferable to
knowing the implementation details here.

Requested by:	Jason Behmer < jason DOT behmer AT isilon DOT com >

8 files changed, 16 insertions, 8 deletions

diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index a3e920d043f2..d3aef7648d55 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -551,7 +551,7 @@ maybe_yield(void)
 {
 
 	if (should_yield())
-		kern_yield(curthread->td_user_pri);
+		kern_yield(PRI_USER);
 }
 
 void
@@ -562,6 +562,8 @@ kern_yield(int prio)
 	td = curthread;
 	DROP_GIANT();
 	thread_lock(td);
+	if (prio == PRI_USER)
+		prio = td->td_user_pri;
 	if (prio >= 0)
 		sched_prio(td, prio);
 	mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index 0f1e35786c9d..8d2fddec6b0f 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -1590,7 +1590,7 @@ userland_sysctl(struct thread *td, int *name, u_int namelen, void *old,
 		SYSCTL_XUNLOCK();
 		if (error != EAGAIN)
 			break;
-		kern_yield(curthread->td_user_pri);
+		kern_yield(PRI_USER);
 	}
 
 	CURVNET_RESTORE();
diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 06e86254046f..0b5e973bc734 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -2234,7 +2234,7 @@ buf_daemon()
 		while (numdirtybuffers > lodirtybuffers) {
 			if (buf_do_flush(NULL) == 0)
 				break;
-			kern_yield(-1);
+			kern_yield(PRI_UNCHANGED);
 		}
 		lodirtybuffers = lodirtysave;
 
diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 7bdb29cf8b67..2e07cf1c7859 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1644,7 +1644,7 @@ __mnt_vnode_next(struct vnode **mvp, struct mount *mp)
 	KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
 	if (should_yield()) {
 		MNT_IUNLOCK(mp);
-		kern_yield(-1);
+		kern_yield(PRI_UNCHANGED);
 		MNT_ILOCK(mp);
 	}
 	vp = TAILQ_NEXT(*mvp, v_nmntvnodes);
diff --git a/sys/kern/vfs_subr.c b/sys/kern/vfs_subr.c
index dead54648dc9..741061d639ef 100644
--- a/sys/kern/vfs_subr.c
+++ b/sys/kern/vfs_subr.c
@@ -718,7 +718,7 @@ next_iter:
 			continue;
 		MNT_IUNLOCK(mp);
 yield:
-		kern_yield(-1);
+		kern_yield(PRI_UNCHANGED);
 relock_mnt:
 		MNT_ILOCK(mp);
 	}
@@ -831,7 +831,7 @@ vnlru_proc(void)
 			vnlru_nowhere++;
 			tsleep(vnlruproc, PPAUSE, "vlrup", hz * 3);
 		} else
-			kern_yield(-1);
+			kern_yield(PRI_UNCHANGED);
 	}
 }
 
diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index 7b5cad1f04fd..e8bcc91cb969 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -491,7 +491,7 @@ vn_rdwr_inchunks(rw, vp, base, len, offset, segflg, ioflg, active_cred,
 			break;
 		offset += chunk;
 		base = (char *)base + chunk;
-		kern_yield(curthread->td_user_pri);
+		kern_yield(PRI_USER);
 	} while (len);
 	if (aresid)
 		*aresid = len + iaresid;
diff --git a/sys/sys/priority.h b/sys/sys/priority.h
index 8ada2db11e20..6548a35c9526 100644
--- a/sys/sys/priority.h
+++ b/sys/sys/priority.h
@@ -117,6 +117,12 @@
 #define	PRI_MIN_IDLE		(224)
 #define	PRI_MAX_IDLE		(PRI_MAX)
 
+#ifdef _KERNEL
+/* Other arguments for kern_yield(9). */
+#define	PRI_USER	-2	/* Change to current user priority. */
+#define	PRI_UNCHANGED	-1	/* Do not change priority. */
+#endif
+
 struct priority {
 	u_char	pri_class;	/* Scheduling class. */
 	u_char	pri_level;	/* Normal priority level. */
diff --git a/sys/ufs/ffs/ffs_softdep.c b/sys/ufs/ffs/ffs_softdep.c
index a6d444158b15..a7ae484fcb1a 100644
--- a/sys/ufs/ffs/ffs_softdep.c
+++ b/sys/ufs/ffs/ffs_softdep.c
@@ -1412,7 +1412,7 @@ softdep_process_worklist(mp, full)
 		 */
 		if (should_yield()) {
 			FREE_LOCK(&lk);
-			kern_yield(-1);
+			kern_yield(PRI_UNCHANGED);
 			bwillwrite();
 			ACQUIRE_LOCK(&lk);
 		}