kernel - poll/select - temporary fix for stalls

* Switch around a conditional to test LWP_SELECT first before attempting
  to make the process runnable.  This seems to fix the race causing
  reported stalls.

diff --git a/sys/kern/sys_generic.c b/sys/kern/sys_generic.c
index 8078bc6..7b2ce4a 100644 (file)
--- a/sys/kern/sys_generic.c
+++ b/sys/kern/sys_generic.c
@@ -974,15 +974,15 @@ retry:
                    24 * 60 * 60 * hz : tvtohz_high(&ttv);
        }
        crit_enter();
+       tsleep_interlock(&selwait, PCATCH);
        if ((lp->lwp_flag & LWP_SELECT) == 0 || nselcoll != ncoll) {
                crit_exit();
                goto retry;
        }
        lp->lwp_flag &= ~LWP_SELECT;
-
-       error = tsleep((caddr_t)&selwait, PCATCH, "select", timo);
-       
+       error = tsleep(&selwait, PCATCH | PINTERLOCKED, "select", timo);
        crit_exit();
+
        if (error == 0)
                goto retry;
 done:
@@ -1118,6 +1118,7 @@ retry:
        lp->lwp_flag &= ~LWP_SELECT;
        error = tsleep(&selwait, PCATCH | PINTERLOCKED, "poll", timo);
        crit_exit();
+
        if (error == 0)
                goto retry;
 done:
@@ -1242,8 +1243,16 @@ selwakeup(struct selinfo *sip)
        if (lp == NULL)
                return;
 
+       /*
+        * This is a temporary hack until the code can be rewritten.
+        * Check LWP_SELECT before assuming we can setrunnable().
+        * Otherwise we might catch the lwp before it actually goes to
+        * sleep.
+        */
        crit_enter();
-       if (lp->lwp_wchan == (caddr_t)&selwait) {
+       if (lp->lwp_flag & LWP_SELECT) {
+               lp->lwp_flag &= ~LWP_SELECT;
+       } else if (lp->lwp_wchan == (caddr_t)&selwait) {
                /*
                 * Flag the process to break the tsleep when
                 * setrunnable is called, but only call setrunnable
@@ -1252,8 +1261,6 @@ selwakeup(struct selinfo *sip)
                lp->lwp_flag |= LWP_BREAKTSLEEP;
                if (p->p_stat != SSTOP)
                        setrunnable(lp);
-       } else if (lp->lwp_flag & LWP_SELECT) {
-               lp->lwp_flag &= ~LWP_SELECT;
        }
        crit_exit();
 }