Module Name: src
Committed By: riastradh
Date: Sun Oct 10 11:20:47 UTC 2021
Modified Files:
src/share/man/man9: pserialize.9
src/sys/kern: subr_pserialize.c
Log Message:
pserialize(9): Lift rule that pserialize_perform be serialized.
There may have been a technical reason for this back when we were
following the expired passive serialization patent to the letter, but
no more -- and this is a real burden for some applications.
To generate a diff of this commit:
cvs rdiff -u -r1.13 -r1.14 src/share/man/man9/pserialize.9
cvs rdiff -u -r1.17 -r1.18 src/sys/kern/subr_pserialize.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/share/man/man9/pserialize.9
diff -u src/share/man/man9/pserialize.9:1.13 src/share/man/man9/pserialize.9:1.14
--- src/share/man/man9/pserialize.9:1.13 Mon Jul 3 21:28:48 2017
+++ src/share/man/man9/pserialize.9 Sun Oct 10 11:20:46 2021
@@ -1,4 +1,4 @@
-.\" $NetBSD: pserialize.9,v 1.13 2017/07/03 21:28:48 wiz Exp $
+.\" $NetBSD: pserialize.9,v 1.14 2021/10/10 11:20:46 riastradh Exp $
.\"
.\" Copyright (c) 2011 The NetBSD Foundation, Inc.
.\" All rights reserved.
@@ -67,9 +67,10 @@ Takes the IPL value returned by
.It Fn pserialize_perform
Perform the passive serialization on the writer side.
Passing of this function ensures that no readers are in action.
-Writers must be additionally serialized with a separate mechanism,
-e.g.
-.Xr mutex 9 .
+Writers are typically additionally serialized with a separate
+mechanism, e.g.
+.Xr mutex 9 ,
+to remove objects used by readers from a published list.
Operation blocks and it may only be performed from thread context.
.El
.\" -----
@@ -152,14 +153,15 @@ readers:
break;
}
}
+ mutex_exit(&frobbotzim.lock);
+
/*
* Wait for all existing readers to complete. New readers will
* not see f because the list no longer points to it.
*/
pserialize_perform(frobbotzim.psz);
- /* Now nobody else can be touching f, so it is safe to free. */
- mutex_exit(&frobbotzim.lock);
+ /* Now nobody else can be touching f, so it is safe to free. */
if (f != NULL)
pool_put(&frotz_pool, f);
.Ed
Index: src/sys/kern/subr_pserialize.c
diff -u src/sys/kern/subr_pserialize.c:1.17 src/sys/kern/subr_pserialize.c:1.18
--- src/sys/kern/subr_pserialize.c:1.17 Thu Dec 5 03:21:29 2019
+++ src/sys/kern/subr_pserialize.c Sun Oct 10 11:20:46 2021
@@ -1,4 +1,4 @@
-/* $NetBSD: subr_pserialize.c,v 1.17 2019/12/05 03:21:29 riastradh Exp $ */
+/* $NetBSD: subr_pserialize.c,v 1.18 2021/10/10 11:20:46 riastradh Exp $ */
/*-
* Copyright (c) 2010, 2011 The NetBSD Foundation, Inc.
@@ -31,7 +31,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.17 2019/12/05 03:21:29 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_pserialize.c,v 1.18 2021/10/10 11:20:46 riastradh Exp $");
#include <sys/param.h>
#include <sys/atomic.h>
@@ -43,7 +43,7 @@ __KERNEL_RCSID(0, "$NetBSD: subr_pserial
#include <sys/xcall.h>
struct pserialize {
- lwp_t * psz_owner;
+ char psz_dummy;
};
static kmutex_t psz_lock __cacheline_aligned;
@@ -86,16 +86,13 @@ void
pserialize_destroy(pserialize_t psz)
{
- KASSERT(psz->psz_owner == NULL);
kmem_free(psz, sizeof(*psz));
}
/*
* pserialize_perform:
*
- * Perform the write side of passive serialization. This operation
- * MUST be serialized at a caller level (e.g. with a mutex or by a
- * single-threaded use).
+ * Perform the write side of passive serialization.
*/
void
pserialize_perform(pserialize_t psz)
@@ -107,22 +104,17 @@ pserialize_perform(pserialize_t psz)
if (__predict_false(panicstr != NULL)) {
return;
}
- KASSERT(psz->psz_owner == NULL);
if (__predict_false(mp_online == false)) {
psz_ev_excl.ev_count++;
return;
}
- psz->psz_owner = curlwp;
-
/*
* Broadcast a NOP to all CPUs and wait until all of them complete.
*/
xc_barrier(XC_HIGHPRI);
- KASSERT(psz->psz_owner == curlwp);
- psz->psz_owner = NULL;
mutex_enter(&psz_lock);
psz_ev_excl.ev_count++;
mutex_exit(&psz_lock);
