[src/trunk]: src/sys Add a condition variable (ex_flwanted) to struct extent ...

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

details:   https://anonhg.NetBSD.org/src/rev/74e005eb733a
branches:  trunk
changeset: 825606:74e005eb733a
user:      skrll <skrll%NetBSD.org@localhost>
date:      Mon Jul 24 19:56:07 2017 +0000

description:
Add a condition variable (ex_flwanted) to struct extent so that ex_flags
becomes an invariant.

Remove strange locking for ex_flags as a result.

diffstat:

 sys/kern/subr_extent.c |  31 +++++++++----------------------
 sys/sys/extent.h       |   3 ++-
 2 files changed, 11 insertions(+), 23 deletions(-)

diffs (113 lines):

diff -r f324d365a655 -r 74e005eb733a sys/kern/subr_extent.c
--- a/sys/kern/subr_extent.c    Mon Jul 24 19:37:41 2017 +0000
+++ b/sys/kern/subr_extent.c    Mon Jul 24 19:56:07 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: subr_extent.c,v 1.80 2016/12/19 13:02:14 cherry Exp $  */
+/*     $NetBSD: subr_extent.c,v 1.81 2017/07/24 19:56:07 skrll Exp $   */
 
 /*-
  * Copyright (c) 1996, 1998, 2007 The NetBSD Foundation, Inc.
@@ -34,7 +34,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_extent.c,v 1.80 2016/12/19 13:02:14 cherry Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_extent.c,v 1.81 2017/07/24 19:56:07 skrll Exp $");
 
 #ifdef _KERNEL
 #ifdef _KERNEL_OPT
@@ -126,17 +126,9 @@
 extent_alloc_region_descriptor(struct extent *ex, int flags)
 {
        struct extent_region *rp;
-       int exflags, error;
+       int error;
 
-       /*
-        * XXX Make a static, create-time flags word, so we don't
-        * XXX have to lock to read it!
-        */
-       mutex_enter(&ex->ex_lock);
-       exflags = ex->ex_flags;
-       mutex_exit(&ex->ex_lock);
-
-       if (exflags & EXF_FIXED) {
+       if (ex->ex_flags & EXF_FIXED) {
                struct extent_fixed *fex = (struct extent_fixed *)ex;
 
                mutex_enter(&ex->ex_lock);
@@ -160,7 +152,7 @@
                                mutex_exit(&ex->ex_lock);
                                return (NULL);
                        }
-                       ex->ex_flags |= EXF_FLWANTED;
+                       ex->ex_flwanted = true;
                        if ((flags & EX_CATCH) != 0)
                                error = cv_wait_sig(&ex->ex_cv, &ex->ex_lock);
                        else {
@@ -199,7 +191,7 @@
                 * just free'ing it back to the system.
                 */
                if (rp->er_flags & ER_ALLOC) {
-                       if (ex->ex_flags & EXF_FLWANTED) {
+                       if (ex->ex_flwanted) {
                                /* Clear all but ER_ALLOC flag. */
                                rp->er_flags = ER_ALLOC;
                                LIST_INSERT_HEAD(&fex->fex_freelist, rp,
@@ -214,7 +206,7 @@
                }
 
  wake_em_up:
-               ex->ex_flags &= ~EXF_FLWANTED;
+               ex->ex_flwanted = false;
                cv_broadcast(&ex->ex_cv);
                return;
        }
@@ -300,6 +292,7 @@
        ex->ex_start = start;
        ex->ex_end = end;
        ex->ex_flags = 0;
+       ex->ex_flwanted = false;
        if (fixed_extent)
                ex->ex_flags |= EXF_FIXED;
        if (flags & EX_NOCOALESCE)
@@ -1009,7 +1002,6 @@
 {
        struct extent_region *rp, *nrp = NULL;
        u_long end = start + (size - 1);
-       int coalesce;
 
 #ifdef DIAGNOSTIC
        /*
@@ -1040,13 +1032,8 @@
        /*
         * If we're allowing coalescing, we must allocate a region
         * descriptor now, since it might block.
-        *
-        * XXX Make a static, create-time flags word, so we don't
-        * XXX have to lock to read it!
         */
-       mutex_enter(&ex->ex_lock);
-       coalesce = (ex->ex_flags & EXF_NOCOALESCE) == 0;
-       mutex_exit(&ex->ex_lock);
+       const bool coalesce = (ex->ex_flags & EXF_NOCOALESCE) == 0;
 
        if (coalesce) {
                /* Allocate a region descriptor. */
diff -r f324d365a655 -r 74e005eb733a sys/sys/extent.h
--- a/sys/sys/extent.h  Mon Jul 24 19:37:41 2017 +0000
+++ b/sys/sys/extent.h  Mon Jul 24 19:56:07 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: extent.h,v 1.20 2017/07/24 19:22:32 skrll Exp $        */
+/*     $NetBSD: extent.h,v 1.21 2017/07/24 19:56:07 skrll Exp $        */
 
 /*-
  * Copyright (c) 1996, 1998 The NetBSD Foundation, Inc.
@@ -55,6 +55,7 @@
        u_long  ex_start;               /* start of extent */
        u_long  ex_end;                 /* end of extent */
        int     ex_flags;               /* misc. information */
+       bool    ex_flwanted;            /* someone asleep on freelist */
 };
 
 struct extent_fixed {