Date: Mon, 1 Feb 2016 14:58:05 +0900
From: Ryota Ozaki <ozak...@netbsd.org>
On Sat, Jan 30, 2016 at 12:43 AM, Taylor R Campbell
<riastr...@netbsd.org> wrote:
> Date: Fri, 29 Jan 2016 17:39:13 +0900
> From: Ryota Ozaki <ozak...@netbsd.org>
>
> I'm thinking applying psref to bridge member list
> that is now using its own version of similar mechanism
> (psz + refcount).
>
> Nice! That sounds like a good application to test, since most of the
> work has been done already and it's mainly a matter of replacing a
> refcount by a psref.
I'm happy if there is a patch of psref.c to -current :)
Here you go, attached! I even compile-tested this one.
> int bound = curlwp->l_pflag & LP_BOUND;
> curlwp->l_pflag |= LP_BOUND;
> ...acquire and release psref...
> curlwp->l_pflag ^= bound ^ LP_BOUND;
>
> [...]
>
> Someone more familiar with the inner workings of LWPs and the
> scheduler should review this, though. And maybe we should invent a
> name lwp_bind/lwp_unbind for this pattern.
I agree; open accesses to l_pflag looks not good idea.
Actually, I think it is fine. There was only one exception I could
find in-tree, LP_VFORKWAIT, and it has been relegated to #if 0. All
other flags are used in l_pflag unlocked, and I believe the scheduler
and interrupt handlers will undo any changes they make -- LP_BOUND,
LP_INTR, LP_OWEUPC, LP_RUNNING, LP_TIMEINTR.
That said, I think naming lwp_bind/lwp_unbind is still a good idea!
Maybe instead curlwp_bind/curlwp_unbind.
/* sys/lwp.h */
static inline int
curlwp_bind(void)
{
int bound;
bound = curlwp->l_pflag & LP_BOUND;
curlwp->l_pflag |= LP_BOUND;
return bound;
}
static inline void
curlwp_unbind(int bound)
{
curlwp->l_pflag ^= bound ^ LP_BOUND;
}
Index: sys/arch/amd64/conf/ALL
===================================================================
RCS file: /cvsroot/src/sys/arch/amd64/conf/ALL,v
retrieving revision 1.33
diff -p -u -r1.33 ALL
--- sys/arch/amd64/conf/ALL 10 Nov 2015 13:01:41 -0000 1.33
+++ sys/arch/amd64/conf/ALL 2 Feb 2016 00:08:33 -0000
@@ -125,6 +125,7 @@ options SYSCALL_STATS # per syscall cou
options SYSCALL_TIMES # per syscall times
options SYSCALL_TIMES_HASCOUNTER # use 'broken' rdtsc (soekris)
options KDTRACE_HOOKS # kernel DTrace hooks
+options PSREF_DEBUG # debug passive references
# Compatibility options
#options COMPAT_NOMID # NetBSD 0.8, 386BSD, and BSDI
Index: sys/arch/i386/conf/ALL
===================================================================
RCS file: /cvsroot/src/sys/arch/i386/conf/ALL,v
retrieving revision 1.397
diff -p -u -r1.397 ALL
--- sys/arch/i386/conf/ALL 25 Oct 2015 22:48:23 -0000 1.397
+++ sys/arch/i386/conf/ALL 2 Feb 2016 00:08:34 -0000
@@ -125,6 +125,7 @@ options SYSCALL_STATS # per syscall cou
options SYSCALL_TIMES # per syscall times
options SYSCALL_TIMES_HASCOUNTER # use 'broken' rdtsc (soekris)
options KDTRACE_HOOKS # kernel DTrace hooks
+options PSREF_DEBUG # debug passive references
# Compatibility options
options COMPAT_NOMID # NetBSD 0.8, 386BSD, and BSDI
Index: sys/conf/files
===================================================================
RCS file: /cvsroot/src/sys/conf/files,v
retrieving revision 1.1152
diff -p -u -r1.1152 files
--- sys/conf/files 9 Dec 2015 18:25:32 -0000 1.1152
+++ sys/conf/files 2 Feb 2016 00:08:34 -0000
@@ -284,6 +284,7 @@ defparam opt_kgdb.h KGDB_DEV KGDB_DEVNA
defflag LOCKDEBUG
defflag SYSCALL_DEBUG
defflag opt_kstack.h KSTACK_CHECK_MAGIC
+defflag opt_psref.h PSREF_DEBUG
# memory (ram) disk options
#
Index: sys/kern/files.kern
===================================================================
RCS file: /cvsroot/src/sys/kern/files.kern,v
retrieving revision 1.10
diff -p -u -r1.10 files.kern
--- sys/kern/files.kern 3 Dec 2015 02:51:00 -0000 1.10
+++ sys/kern/files.kern 2 Feb 2016 00:08:35 -0000
@@ -125,6 +125,7 @@ file kern/subr_pool.c kern
file kern/subr_prf.c kern
file kern/subr_prof.c kern
file kern/subr_pserialize.c kern
+file kern/subr_psref.c kern
file kern/subr_specificdata.c kern
file kern/subr_tftproot.c tftproot
file kern/subr_time.c kern
Index: sys/kern/subr_psref.c
===================================================================
RCS file: sys/kern/subr_psref.c
diff -N sys/kern/subr_psref.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ sys/kern/subr_psref.c 2 Feb 2016 00:08:35 -0000
@@ -0,0 +1,409 @@
+/* $NetBSD$ */
+
+/*-
+ * Copyright (c) 2016 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Taylor R. Campbell.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ * Passive references
+ *
+ * Passive references are references to objects that guarantee the
+ * object will not be destroyed until the reference is released.
+ *
+ * Passive references require no interprocessor synchronization to
+ * acquire or release. However, destroying the target of passive
+ * references requires expensive interprocessor synchronization --
+ * xcalls to determine on which CPUs the object is still in use.
+ *
+ * Passive references may be held only on a single CPU and by a
+ * single LWP. They require the caller to allocate a little stack
+ * space, a struct psref object. Sleeping while a passive
+ * reference is held is allowed, provided that the owner's LWP is
+ * bound to a CPU -- e.g., the owner is a softint or a bound
+ * kthread. However, sleeping should be kept to a short duration,
+ * e.g. sleeping on an adaptive lock.
+ *
+ * Passive references serve as an intermediate stage between
+ * reference counting and passive serialization (pserialize(9)):
+ *
+ * - If you need references to transfer from CPU to CPU or LWP to
+ * LWP, or if you need long-term references, you must use
+ * reference counting, e.g. with atomic operations or locks,
+ * which incurs interprocessor synchronization for every use --
+ * cheaper than an xcall, but not scalable.
+ *
+ * - If all users *guarantee* that they will not sleep, then it is
+ * not necessary to use passive references: you may as well just
+ * use the even cheaper pserialize(9), because you have
+ * satisfied the requirements of a pserialize read section.
+ */
+
+#include <sys/cdefs.h>
+__KERNEL_RCSID(0, "$NetBSD$");
+
+#include <sys/types.h>
+#include <sys/condvar.h>
+#include <sys/cpu.h>
+#include <sys/intr.h>
+#include <sys/kmem.h>
+#include <sys/lwp.h>
+#include <sys/mutex.h>
+#include <sys/percpu.h>
+#include <sys/psref.h>
+#include <sys/queue.h>
+#include <sys/xcall.h>
+
+LIST_HEAD(psref_head, psref);
+
+/*
+ * struct psref_class
+ *
+ * Private global state for a class of passive reference targets.
+ * Opaque to callers.
+ */
+struct psref_class {
+ kmutex_t prc_lock;
+ kcondvar_t prc_cv;
+ struct percpu *prc_percpu; /* struct psref_cpu */
+ ipl_cookie_t prc_iplcookie;
+};
+
+/*
+ * struct psref_cpu
+ *
+ * Private per-CPU state for a class of passive reference targets.
+ * Not exposed by the API.
+ */
+struct psref_cpu {
+ struct psref_head pcpu_head;
+};
+
+/*
+ * psref_class_create(name, ipl)
+ *
+ * Create a new passive reference class, with the given wchan name
+ * and ipl.
+ */
+struct psref_class *
+psref_class_create(const char *name, int ipl)
+{
+ struct psref_class *class;
+
+ ASSERT_SLEEPABLE();
+
+ class = kmem_alloc(sizeof(*class), KM_SLEEP);
+ if (class == NULL)
+ goto fail0;
+
+ class->prc_percpu = percpu_alloc(sizeof(struct psref_cpu));
+ if (class->prc_percpu == NULL)
+ goto fail1;
+
+ mutex_init(&class->prc_lock, MUTEX_DEFAULT, ipl);
+ cv_init(&class->prc_cv, name);
+ class->prc_iplcookie = makeiplcookie(ipl);
+
+fail1: kmem_free(class, sizeof(*class));
+fail0: return NULL;
+}
+
+#if DIAGNOSTIC
+static void
+psref_cpu_drained_p(void *p, void *cookie, struct cpu_info *ci __unused)
+{
+ struct psref_cpu *pcpu = p;
+ bool *retp = cookie;
+
+ if (!LIST_EMPTY(&pcpu->pcpu_head))
+ *retp = false;
+}
+
+static bool
+psref_class_drained_p(struct psref_class *prc)
+{
+ bool ret = true;
+
+ percpu_foreach(prc->prc_percpu, &psref_cpu_drained_p, &ret);
+
+ return ret;
+}
+#endif /* DIAGNOSTIC */
+
+/*
+ * psref_class_destroy(class)
+ *
+ * Destroy a passive reference class and free memory associated
+ * with it. All targets in this class must have been drained and
+ * destroyed already.
+ */
+void
+psref_class_destroy(struct psref_class *class)
+{
+
+ KASSERT(psref_class_drained_p(class));
+
+ cv_destroy(&class->prc_cv);
+ mutex_destroy(&class->prc_lock);
+ percpu_free(class->prc_percpu, sizeof(struct psref_cpu));
+ kmem_free(class, sizeof(*class));
+}
+
+/*
+ * psref_target_init(target, class)
+ *
+ * Initialize a passive reference target in the specified class.
+ * The caller is responsible for issuing a membar_producer before
+ * exposing a pointer to the target to other CPUs.
+ */
+void
+psref_target_init(struct psref_target *target, struct psref_class *class)
+{
+
+ target->prt_draining = false;
+#ifdef PSREF_DEBUG
+ target->prt_class = class;
+#endif
+}
+
+/*
+ * psref_target_destroy(target, class)
+ *
+ * Destroy a passive reference target. It must have previously
+ * been drained.
+ */
+void
+psref_target_destroy(struct psref_target *target, struct psref_class *class)
+{
+
+ KASSERT(target->prt_draining);
+#ifdef PSREF_DEBUG
+ KASSERT(target->prt_class == class);
+ target->prt_class = NULL;
+#endif
+}
+
+/*
+ * psref_acquire(psref, target, class)
+ *
+ * Try to acquire a passive reference to the specified target,
+ * which must be in the specified class. On success, returns
+ * zero; on failure, returns a nonzero error code. If the target
+ * is draining, returns ENOENT.
+ *
+ * The caller must guarantee that it will not switch CPUs before
+ * releasing the passive reference, either by disabling
+ * kpreemption and avoiding sleeps, or by being in a softint or in
+ * an LWP bound to a CPU.
+ */
+int
+psref_acquire(struct psref *psref, struct psref_target *target,
+ struct psref_class *class)
+{
+ struct psref_cpu *pcpu;
+ int s, error;
+
+ KASSERTMSG((kpreempt_disabled() || cpu_softintr_p() ||
+ ISSET(curlwp->l_pflag, LP_BOUND)),
+ "passive references are CPU-local,"
+ " but preemption is enabled and the caller is not"
+ " in a softint or CPU-bound LWP");
+
+#ifdef PSREF_DEBUG
+ KASSERT(target->prt_class == class);
+#endif
+
+ /* Block interrupts and acquire the current CPU's reference list. */
+ s = splraiseipl(class->prc_iplcookie);
+ pcpu = percpu_getref(class->prc_percpu);
+
+ /* Is this target going away? */
+ if (__predict_false(target->prt_draining)) {
+ /* Yes: fail. */
+ error = ENOENT;
+ } else {
+ /* No: record our reference. */
+ LIST_INSERT_HEAD(&pcpu->pcpu_head, psref, psref_entry);
+ psref->psref_target = target;
+#ifdef PSREF_DEBUG
+ psref->psref_lwp = curlwp;
+ psref->psref_cpu = curcpu();
+#endif
+ error = 0;
+ }
+
+ /* Release the CPU list and restore interrupts. */
+ percpu_putref(class->prc_percpu);
+ splx(s);
+
+ return error;
+}
+
+/*
+ * psref_release(psref, target, class)
+ *
+ * Release a passive reference to the specified target, which must
+ * be in the specified class.
+ *
+ * The caller must not have switched CPUs or LWPs since acquiring
+ * the passive reference.
+ */
+void
+psref_release(struct psref *psref, struct psref_target *target,
+ struct psref_class *class)
+{
+ int s;
+
+ KASSERTMSG((kpreempt_disabled() || cpu_softintr_p() ||
+ ISSET(curlwp->l_pflag, LP_BOUND)),
+ "passive references are CPU-local,"
+ " but preemption is enabled and the caller is not"
+ " in a softint or CPU-bound LWP");
+
+ KASSERT(psref->psref_target == target);
+#ifdef PSREF_DEBUG
+ KASSERT(target->prt_class == class);
+ KASSERTMSG((psref->psref_lwp == curlwp),
+ "passive reference transferred from lwp %p to lwp %p",
+ psref->psref_lwp, curlwp);
+ KASSERTMSG((psref->psref_cpu == curcpu()),
+ "passive reference transferred from CPU %u to CPU %u",
+ cpu_index(psref->psref_cpu), cpu_index(curcpu()));
+#endif
+
+ /*
+ * Block interrupts and remove the psref from the current CPU's
+ * list. No need to percpu_getref or get the head of the list,
+ * and the caller guarantees that we are bound to a CPU anyway
+ * (as does blocking interrupts).
+ */
+ s = splraiseipl(class->prc_iplcookie);
+ LIST_REMOVE(psref, psref_entry);
+ splx(s);
+
+ /* If someone is waiting for users to drain, notify 'em. */
+ if (__predict_false(target->prt_draining))
+ cv_broadcast(&class->prc_cv);
+}
+
+/*
+ * struct psreffed
+ *
+ * Global state for draining a psref target.
+ */
+struct psreffed {
+ struct psref_class *class;
+ struct psref_target *target;
+ bool ret;
+};
+
+static void
+psreffed_p_xc(void *cookie0, void *cookie1 __unused)
+{
+ struct psreffed *P = cookie0;
+ struct psref_class *class = P->class;
+ struct psref_target *target = P->target;
+ struct psref_cpu *pcpu;
+ struct psref *psref;
+ int s;
+
+ /* Block interrupts and acquire the current CPU's reference list. */
+ s = splraiseipl(class->prc_iplcookie);
+ pcpu = percpu_getref(class->prc_percpu);
+
+ /*
+ * Check the CPU's reference list for any references to this
+ * target. This loop shouldn't take very long because any
+ * single CPU should hold only a small number of references at
+ * any given time unless there is a bug.
+ */
+ LIST_FOREACH(psref, &pcpu->pcpu_head, psref_entry) {
+ if (psref->psref_target == target) {
+ /*
+ * No need to lock anything here: every write
+ * transitions from false to true, so as long
+ * as any write goes through we're good. No
+ * need for a memory barrier because this is
+ * read only after xc_wait, which has already
+ * issued any necessary memory barriers.
+ */
+ P->ret = true;
+ break;
+ }
+ }
+
+ /* Release the CPU list and restore interrupts. */
+ percpu_putref(class->prc_percpu);
+ splx(s);
+}
+
+static bool
+psreffed_p(struct psref_target *target, struct psref_class *class)
+{
+ struct psreffed P = {
+ .class = class,
+ .target = target,
+ .ret = false,
+ };
+
+ xc_wait(xc_broadcast(0, &psreffed_p_xc, &P, NULL));
+
+ return P.ret;
+}
+
+/*
+ * psref_target_drain(target, class)
+ *
+ * Prevent new references to target and wait for existing ones to
+ * drain. May sleep.
+ */
+void
+psref_target_drain(struct psref_target *target, struct psref_class *class)
+{
+
+#ifdef PSREF_DEBUG
+ KASSERT(target->prt_class == class);
+#endif
+
+ ASSERT_SLEEPABLE();
+ KASSERT(!target->prt_draining);
+ target->prt_draining = true;
+
+ /* Wait until there are no more references on any CPU. */
+ while (psreffed_p(target, class)) {
+ /*
+ * This enter/wait/exit business looks wrong, but it is
+ * both necessary, because psreffed_p performs a
+ * low-priority xcall and hence cannot run while a
+ * mutex is locked, and OK, because the wait is timed
+ * -- explicit wakeups are only an optimization.
+ */
+ mutex_enter(&class->prc_lock);
+ (void)cv_timedwait(&class->prc_cv, &class->prc_lock, 1);
+ mutex_exit(&class->prc_lock);
+ }
+}
Index: sys/sys/psref.h
===================================================================
RCS file: sys/sys/psref.h
diff -N sys/sys/psref.h
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ sys/sys/psref.h 2 Feb 2016 00:08:36 -0000
@@ -0,0 +1,107 @@
+/* $NetBSD$ */
+
+/*-
+ * Copyright (c) 2016 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Taylor R. Campbell.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _SYS_PSREF_H
+#define _SYS_PSREF_H
+
+#include <sys/types.h>
+#include <sys/queue.h>
+
+/*
+ * PSREF_DEBUG
+ *
+ * If nonzero, enable debugging of psrefs. WARNING: This changes
+ * the ABI by adding extra fields to struct psref_target and
+ * struct psref, which are exposed to callers and embedded in
+ * other structures.
+ */
+#ifdef _KERNEL_OPT
+#include "opt_psref.h"
+#endif
+
+struct cpu_info;
+struct lwp;
+
+struct psref;
+struct psref_class;
+struct psref_target;
+
+/*
+ * struct psref_target
+ *
+ * Bookkeeping for an object to which users can acquire passive
+ * references. This is compact so that it can easily be embedded
+ * into many multitudes of objects, e.g. IP packet flows.
+ *
+ * prt_draining is false on initialization, and may be written
+ * only once, to make it true, when someone with exclusive access
+ * to it is about to drain the target.
+ */
+struct psref_target {
+ bool prt_draining;
+#ifdef PSREF_DEBUG
+ struct psref_class *prt_class;
+#endif
+};
+
+/*
+ * struct psref
+ *
+ * Bookkeeping for a single passive reference. There should only
+ * be a few of these per CPU in the system at once, no matter how
+ * many targets are stored, so these are a bit larger than struct
+ * psref_target. The contents of struct psref may be read and
+ * written only on the local CPU.
+ */
+struct psref {
+ LIST_ENTRY(psref) psref_entry;
+ struct psref_target *psref_target;
+#ifdef PSREF_DEBUG
+ struct lwp *psref_lwp;
+ struct cpu_info *psref_cpu;
+#endif
+};
+
+struct psref_class *
+ psref_class_create(const char *, int);
+void psref_class_destroy(struct psref_class *);
+
+void psref_target_init(struct psref_target *, struct psref_class *);
+void psref_target_destroy(struct psref_target *, struct psref_class *);
+
+int psref_acquire(struct psref *, struct psref_target *,
+ struct psref_class *);
+void psref_release(struct psref *, struct psref_target *,
+ struct psref_class *);
+
+void psref_target_drain(struct psref_target *, struct psref_class *);
+
+#endif /* _SYS_PSREF_H */
