use rwlock in i386 mem.c

[Ted Unangst]

The homegrown physlock is a little weird looking. rwlock is easier to read and
reason about. (there are more like this, but i am starting here.)


Index: i386/i386/mem.c
===================================================================
RCS file: /cvs/src/sys/arch/i386/i386/mem.c,v
retrieving revision 1.47
diff -u -p -r1.47 mem.c
--- i386/i386/mem.c     8 Sep 2015 07:12:56 -0000       1.47
+++ i386/i386/mem.c     27 Jul 2016 15:03:32 -0000
@@ -48,6 +48,7 @@
 #include <sys/malloc.h>
 #include <sys/memrange.h>
 #include <sys/fcntl.h>
+#include <sys/rwlock.h>
 
 #include <machine/cpu.h>
 #include <machine/conf.h>
@@ -119,18 +120,13 @@ mmrw(dev_t dev, struct uio *uio, int fla
        size_t c;
        struct iovec *iov;
        int error = 0;
-       static int physlock;
+       static struct rwlock physlock = RWLOCK_INITIALIZER("mmrw");
 
        if (minor(dev) == 0) {
                /* lock against other uses of shared vmmap */
-               while (physlock > 0) {
-                       physlock++;
-                       error = tsleep((caddr_t)&physlock, PZERO | PCATCH,
-                           "mmrw", 0);
-                       if (error)
-                               return (error);
-               }
-               physlock = 1;
+               error = rw_enter(&physlock, RW_WRITE | RW_INTR);
+               if (error)
+                       return (error);
        }
        while (uio->uio_resid > 0 && error == 0) {
                iov = uio->uio_iov;
@@ -197,9 +193,7 @@ mmrw(dev_t dev, struct uio *uio, int fla
                uio->uio_resid -= c;
        }
        if (minor(dev) == 0) {
-               if (physlock > 1)
-                       wakeup((caddr_t)&physlock);
-               physlock = 0;
+               rw_exit(&physlock);
        }
        return (error);
 }