[src/trunk]: src/sys/kern - do_sched_getparam: release locks earlier.

[yamt <yamt%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/11c512ebe8d1
branches:  trunk
changeset: 778791:11c512ebe8d1
user:      yamt <yamt%NetBSD.org@localhost>
date:      Fri Apr 13 15:27:13 2012 +0000

description:
- do_sched_getparam: release locks earlier.
- add comments

diffstat:

 sys/kern/sys_sched.c |  29 +++++++++++++++++++++++------
 1 files changed, 23 insertions(+), 6 deletions(-)

diffs (79 lines):

diff -r a1ec3a7a35d4 -r 11c512ebe8d1 sys/kern/sys_sched.c
--- a/sys/kern/sys_sched.c      Fri Apr 13 15:14:58 2012 +0000
+++ b/sys/kern/sys_sched.c      Fri Apr 13 15:27:13 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sys_sched.c,v 1.40 2012/02/19 21:06:56 rmind Exp $     */
+/*     $NetBSD: sys_sched.c,v 1.41 2012/04/13 15:27:13 yamt Exp $      */
 
 /*
  * Copyright (c) 2008, 2011 Mindaugas Rasiukevicius <rmind at NetBSD org>
@@ -42,7 +42,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_sched.c,v 1.40 2012/02/19 21:06:56 rmind Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_sched.c,v 1.41 2012/04/13 15:27:13 yamt Exp $");
 
 #include <sys/param.h>
 
@@ -92,6 +92,11 @@
        /* Real-time -> time-sharing */
        if (policy == SCHED_OTHER) {
                KASSERT(l->l_class == SCHED_FIFO || l->l_class == SCHED_RR);
+               /*
+                * this is a bit arbitrary because the priority is dynamic
+                * for SCHED_OTHER threads and will likely be changed by
+                * the scheduler soon anyway.
+                */
                return l->l_priority - PRI_USER_RT;
        }
 
@@ -214,6 +219,11 @@
        return error;
 }
 
+/*
+ * do_sched_getparam:
+ *
+ * if lid=0, returns the parameter of the first LWP in the process.
+ */
 int
 do_sched_getparam(pid_t pid, lwpid_t lid, int *policy,
     struct sched_param *params)
@@ -222,8 +232,7 @@
        struct lwp *t;
        int error, lpolicy;
 
-       /* Locks the LWP */
-       t = lwp_find2(pid, lid);
+       t = lwp_find2(pid, lid); /* acquire p_lock */
        if (t == NULL)
                return ESRCH;
 
@@ -238,7 +247,17 @@
        lwp_lock(t);
        lparams.sched_priority = t->l_priority;
        lpolicy = t->l_class;
+       lwp_unlock(t);
+       mutex_exit(t->l_proc->p_lock);
 
+       /*
+        * convert to the user-visible priority value.
+        * it's an inversion of convert_pri().
+        *
+        * the SCHED_OTHER case is a bit arbitrary given that
+        *      - we don't allow setting the priority.
+        *      - the priority is dynamic.
+        */
        switch (lpolicy) {
        case SCHED_OTHER:
                lparams.sched_priority -= PRI_USER;
@@ -255,8 +274,6 @@
        if (params != NULL)
                *params = lparams;
 
-       lwp_unlock(t);
-       mutex_exit(t->l_proc->p_lock);
        return error;
 }