[src/trunk]: src fix vmem_alloc() to never return an error for VM_SLEEP reque...

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

details:   https://anonhg.NetBSD.org/src/rev/d2563916c1e2
branches:  trunk
changeset: 343860:d2563916c1e2
user:      chs <chs%NetBSD.org@localhost>
date:      Mon Feb 29 00:34:17 2016 +0000

description:
fix vmem_alloc() to never return an error for VM_SLEEP requests,
thus fixing kmem_alloc() to never return NULL for KM_SLEEP requests.
instead these operations will retry forever, which was the intent.

diffstat:

 share/man/man9/kmem.9 |  19 ++------------
 share/man/man9/vmem.9 |  65 ++++++++++++++++++++++++++++----------------------
 sys/kern/subr_kmem.c  |  16 +++++++++---
 sys/kern/subr_vmem.c  |  55 +++++++++++++++++++++++++++---------------
 4 files changed, 86 insertions(+), 69 deletions(-)

diffs (truncated from 442 to 300 lines):

diff -r b39944709569 -r d2563916c1e2 share/man/man9/kmem.9
--- a/share/man/man9/kmem.9     Mon Feb 29 00:17:54 2016 +0000
+++ b/share/man/man9/kmem.9     Mon Feb 29 00:34:17 2016 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: kmem.9,v 1.19 2015/12/11 10:05:17 wiz Exp $
+.\"    $NetBSD: kmem.9,v 1.20 2016/02/29 00:34:17 chs Exp $
 .\"
 .\" Copyright (c)2006 YAMAMOTO Takashi,
 .\" All rights reserved.
@@ -25,7 +25,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\" ------------------------------------------------------------
-.Dd December 10, 2015
+.Dd February 28, 2016
 .Dt KMEM 9
 .Os
 .\" ------------------------------------------------------------
@@ -77,15 +77,9 @@
 .It Dv KM_SLEEP
 If the allocation cannot be satisfied immediately, sleep until enough
 memory is available.
-Note that this does not mean that if
+If
 .Dv KM_SLEEP
 is specified, then the allocation cannot fail.
-Under resource stress conditions, the allocation can fail and the
-function will return
-.Dv NULL .
-One such scenario is when the allocation size is larger than it can ever
-be allocated; another is when the system memory resources are exhausted
-to even allocate pools of pages.
 .It Dv KM_NOSLEEP
 Don't sleep.
 Immediately return
@@ -143,9 +137,6 @@
 .Fn kmem_alloc
 or
 .Fn kmem_zalloc .
-One such scenario is when the allocation size is larger than it can ever
-be allocated; another is when the system memory resources are exhausted
-to even allocate pools of pages.
 .It Fa size
 The size of the memory being freed, in bytes.
 It must be the same as the
@@ -185,10 +176,6 @@
 .Fn kmem_free
 may also block.
 .Pp
-Always check the return value of the allocators, even when
-.Dv KM_SLEEP
-is specified to avoid kernel crashes during resource stress conditions.
-.Pp
 For some locks this is permissible or even unavoidable.
 For others, particularly locks that may be taken from soft interrupt context,
 it is a serious problem.
diff -r b39944709569 -r d2563916c1e2 share/man/man9/vmem.9
--- a/share/man/man9/vmem.9     Mon Feb 29 00:17:54 2016 +0000
+++ b/share/man/man9/vmem.9     Mon Feb 29 00:34:17 2016 +0000
@@ -1,4 +1,4 @@
-.\"    $NetBSD: vmem.9,v 1.15 2013/01/29 22:02:17 wiz Exp $
+.\"    $NetBSD: vmem.9,v 1.16 2016/02/29 00:34:17 chs Exp $
 .\"
 .\" Copyright (c)2006 YAMAMOTO Takashi,
 .\" All rights reserved.
@@ -25,7 +25,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\" ------------------------------------------------------------
-.Dd January 29, 2013
+.Dd February 28, 2016
 .Dt VMEM 9
 .Os
 .\" ------------------------------------------------------------
@@ -83,7 +83,7 @@
 .Fn vmem_create
 creates a new vmem arena.
 .Pp
-.Bl -tag -width qcache_max
+.Bl -tag -offset indent -width qcache_max
 .It Fa name
 The string to describe the vmem.
 .It Fa base
@@ -118,7 +118,7 @@
 to import a span of size at least
 .Fa size .
 .Fa allocfn
-should accept the same
+must accept the same
 .Fa flags
 as
 .Fn vmem_alloc .
@@ -169,7 +169,8 @@
 Either of:
 .Bl -tag -width VM_NOSLEEP
 .It Dv VM_SLEEP
-Can sleep until enough resources are available.
+If the allocation cannot be satisfied immediately, sleep until enough
+resources are available.
 .It Dv VM_NOSLEEP
 Don't sleep.
 Immediately return
@@ -184,7 +185,7 @@
 .Fn vmem_xcreate
 creates a new vmem arena.
 .Pp
-.Bl -tag -width qcache_max
+.Bl -tag -offset indent -width qcache_max
 .It Fa name
 The string to describe the vmem.
 .It Fa base
@@ -220,7 +221,7 @@
 to import a span of size at least
 .Fa size .
 .Fa allocfn
-should accept the same
+must accept the same
 .Fa flags
 as
 .Fn vmem_alloc .
@@ -274,7 +275,8 @@
 Either of:
 .Bl -tag -width VM_NOSLEEP
 .It Dv VM_SLEEP
-Can sleep until enough resources are available.
+If the allocation cannot be satisfied immediately, sleep until enough
+resources are available.
 .It Dv VM_NOSLEEP
 Don't sleep.
 Immediately return
@@ -297,23 +299,26 @@
 on success,
 .Dv ENOMEM
 on failure.
-.Fa flags
-should be one of:
+.Bl -tag -offset indent -width flags
+.It Fa flags
+Either of:
 .Bl -tag -width VM_NOSLEEP
 .It Dv VM_SLEEP
-Can sleep until enough resources are available.
+If the allocation cannot be satisfied immediately, sleep until enough
+resources are available.
 .It Dv VM_NOSLEEP
 Don't sleep.
 Immediately return
 .Dv ENOMEM
 if there are not enough resources available.
 .El
+.El
 .Pp
 .\" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 .Fn vmem_xalloc
 allocates a resource from the arena.
 .Pp
-.Bl -tag -width nocross
+.Bl -tag -offset indent -width nocross
 .It Fa vm
 The arena which we allocate from.
 .It Fa size
@@ -333,10 +338,10 @@
 .Fa align
 is zero,
 .Fa phase
-should be zero.
+must be zero.
 Otherwise,
 .Fa phase
-should be smaller than
+must be smaller than
 .Fa align .
 .It Fa nocross
 Request a resource which doesn't cross
@@ -353,7 +358,7 @@
 .It Fa flags
 A bitwise OR of an allocation strategy and a sleep flag.
 .Pp
-The allocation strategy is one of:
+The allocation strategy must be one of:
 .Bl -tag -width VM_INSTANTFIT
 .It Dv VM_BESTFIT
 Prefer space efficiency.
@@ -361,10 +366,11 @@
 Prefer performance.
 .El
 .Pp
-The sleep flag should be one of:
+The sleep flag must be one of:
 .Bl -tag -width VM_NOSLEEP
 .It Dv VM_SLEEP
-Can sleep until enough resources are available.
+If the allocation cannot be satisfied immediately, sleep until enough
+resources are available.
 .It Dv VM_NOSLEEP
 Don't sleep.
 Immediately return
@@ -386,14 +392,14 @@
 .Fn vmem_xalloc
 to the arena.
 .Pp
-.Bl -tag -width addr
+.Bl -tag -offset indent -width addr
 .It Fa vm
 The arena which we free to.
 .It Fa addr
 The resource being freed.
-It must be the one returned by
+It must have been allocated via
 .Fn vmem_xalloc .
-Notably, it must not be the one from
+Notably, it must not have been allocated via
 .Fn vmem_alloc .
 Otherwise, the behaviour is undefined.
 .It Fa size
@@ -408,7 +414,7 @@
 .Fn vmem_alloc
 allocates a resource from the arena.
 .Pp
-.Bl -tag -width flags
+.Bl -tag -offset indent -width flags
 .It Fa vm
 The arena which we allocate from.
 .It Fa size
@@ -416,7 +422,7 @@
 .It Fa flags
 A bitwise OR of an allocation strategy and a sleep flag.
 .Pp
-The allocation strategy is one of:
+The allocation strategy must be one of:
 .Bl -tag -width VM_INSTANTFIT
 .It Dv VM_BESTFIT
 Prefer space efficiency.
@@ -424,10 +430,11 @@
 Prefer performance.
 .El
 .Pp
-The sleep flag should be one of:
+The sleep flag must be one of:
 .Bl -tag -width VM_NOSLEEP
 .It Dv VM_SLEEP
-Can sleep until enough resources are available.
+If the allocation cannot be satisfied immediately, sleep until enough
+resources are available.
 .It Dv VM_NOSLEEP
 Don't sleep.
 Immediately return
@@ -449,14 +456,14 @@
 .Fn vmem_alloc
 to the arena.
 .Pp
-.Bl -tag -width addr
+.Bl -tag -offset indent -width addr
 .It Fa vm
 The arena which we free to.
 .It Fa addr
 The resource being freed.
-It must be the one returned by
+It must have been allocated via
 .Fn vmem_alloc .
-Notably, it must not be the one from
+Notably, it must not have been allocated via
 .Fn vmem_xalloc .
 Otherwise, the behaviour is undefined.
 .It Fa size
@@ -471,10 +478,10 @@
 .Fn vmem_destroy
 destroys a vmem arena.
 .Pp
-.Bl -tag -width vm
+.Bl -tag -offset indent -width vm
 .It Fa vm
 The vmem arena being destroyed.
-The caller should ensure that no one will use it anymore.
+The caller must ensure that no one will use it anymore.
 .El
 .\" ------------------------------------------------------------
 .Sh RETURN VALUES
diff -r b39944709569 -r d2563916c1e2 sys/kern/subr_kmem.c
--- a/sys/kern/subr_kmem.c      Mon Feb 29 00:17:54 2016 +0000
+++ b/sys/kern/subr_kmem.c      Mon Feb 29 00:34:17 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: subr_kmem.c,v 1.61 2015/07/27 09:24:28 maxv Exp $      */
+/*     $NetBSD: subr_kmem.c,v 1.62 2016/02/29 00:34:17 chs Exp $       */
 
 /*-
  * Copyright (c) 2009-2015 The NetBSD Foundation, Inc.
@@ -100,7 +100,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_kmem.c,v 1.61 2015/07/27 09:24:28 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_kmem.c,v 1.62 2016/02/29 00:34:17 chs Exp $");
 
 #include <sys/param.h>
 #include <sys/callback.h>
@@ -383,9 +383,13 @@
 void *
 kmem_alloc(size_t size, km_flag_t kmflags)
 {