From mboxrd@z Thu Jan  1 00:00:00 1970
From: paulmck@linux.vnet.ibm.com (Paul E. McKenney)
Date: Mon, 14 Feb 2011 16:54:30 -0800
Subject: [ltt-dev] [rp] [PATCH RFC] v2 call_rcu() interface for
	userspace-rcu
In-Reply-To: <20110214153844.GA27876@Krystal>
References: <20110211000832.GA14604@linux.vnet.ibm.com>
	<20110212014643.GA6349@Krystal>
	<20110212061257.GA2476@linux.vnet.ibm.com>
	<20110214153844.GA27876@Krystal>
Message-ID: <20110215005430.GS2256@linux.vnet.ibm.com>

On Mon, Feb 14, 2011 at 10:38:44AM -0500, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck at linux.vnet.ibm.com) wrote:
> > On Fri, Feb 11, 2011 at 08:46:44PM -0500, Mathieu Desnoyers wrote:
> > > * Paul E. McKenney (paulmck at linux.vnet.ibm.com) wrote:
> > > > Adds call_rcu(), with RCU threads to invoke the callbacks.  By default,
> > > > there will be one such RCU thread per process, created the first time
> > > > that call_rcu() is invoked.  On systems supporting sched_getcpu(), it
> > > > is possible to create one RCU thread per CPU by calling
> > > > create_all_cpu_call_rcu_data().
> > > > 
> > > > This version includes feedback from Mathieu Desnoyers and forward-ports
> > > > to the new cds naming scheme.  Note that v1 was posted on October 29th.
> > > 
> > > Hi Paul,
> > > 
> > > The interfaces have improved a lot, thanks ! Here are a few comments,
> > > 
> > > > 
> > > > Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> > > > 
> > > > diff --git a/Makefile.am b/Makefile.am
> > > > index 79a7152..64bb299 100644
> > > > --- a/Makefile.am
> > > > +++ b/Makefile.am
> > > > @@ -29,8 +29,8 @@ COMPAT+=compat_futex.c
> > > >  endif
> > > >  
> > > >  lib_LTLIBRARIES = liburcu.la liburcu-qsbr.la liburcu-mb.la liburcu-signal.la \
> > > > -		  liburcu-bp.la liburcu-defer.la libwfqueue.la libwfstack.la \
> > > > -		  librculfqueue.la librculfstack.la
> > > > +		  liburcu-bp.la liburcu-defer.la liburcu-call.la \
> > > > +		  libwfqueue.la libwfstack.la librculfqueue.la librculfstack.la
> > > >  
> > > >  liburcu_la_SOURCES = urcu.c urcu-pointer.c $(COMPAT)
> > > >  
> > > > @@ -44,6 +44,7 @@ liburcu_signal_la_CFLAGS = -DRCU_SIGNAL
> > > >  
> > > >  liburcu_bp_la_SOURCES = urcu-bp.c urcu-pointer.c $(COMPAT)
> > > >  
> > > > +liburcu_call_la_SOURCES = urcu-call-rcu.c $(COMPAT)
> > > >  liburcu_defer_la_SOURCES = urcu-defer.c $(COMPAT)
> > > >  
> > > >  libwfqueue_la_SOURCES = wfqueue.c $(COMPAT)
> > > > diff --git a/configure.ac b/configure.ac
> > > > index 02780e7..88771d4 100644
> > > > --- a/configure.ac
> > > > +++ b/configure.ac
> > > > @@ -34,7 +34,7 @@ AC_TYPE_SIZE_T
> > > >  # Checks for library functions.
> > > >  AC_FUNC_MALLOC
> > > >  AC_FUNC_MMAP
> > > > -AC_CHECK_FUNCS([bzero gettimeofday munmap strtoul])
> > > > +AC_CHECK_FUNCS([bzero gettimeofday munmap sched_getcpu strtoul sysconf])
> > > >  # Find arch type
> > > >  case $host_cpu in
> > > > diff --git a/tests/Makefile.am b/tests/Makefile.am
> > > > index a43dd75..3c025a4 100644
> > > > --- a/tests/Makefile.am
> > > > +++ b/tests/Makefile.am
> > > > @@ -1,5 +1,5 @@
> > > >  AM_LDFLAGS=-lpthread
> > > > -AM_CFLAGS=-I$(top_srcdir) -I$(top_builddir)
> > > > +AM_CFLAGS=-I$(top_srcdir) -I$(top_builddir) -g
> > > 
> > > It makes me think: I noticed this week that -Wall is missing from the top level
> > > build options. We should really add it.
> > 
> > Fair enough.  It did find a nasty uninitialized variable, so worth it in
> > this case.  The ignored return values from write() I leave to you.  ;-)
> > Ditto the "warning: value computed is not used" in rculfqueue-static.h.
> 
> OK, I'll wait for your patches before I change anything though.

Thank you!  (Sorry to be slow today, I will get it done tomorrow.)

> > > >  noinst_PROGRAMS = test_urcu test_urcu_dynamic_link test_urcu_timing \
> > > >  	test_urcu_signal test_urcu_signal_dynamic_link test_urcu_signal_timing \
> > > > @@ -28,20 +28,21 @@ if COMPAT_FUTEX
> > > >  COMPAT+=$(top_srcdir)/compat_futex.c
> > > >  endif
> > > >  
> > > > -URCU=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > > > -URCU_QSBR=$(top_srcdir)/urcu-qsbr.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > > > +URCU=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > > > +URCU_QSBR=$(top_srcdir)/urcu-qsbr.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > > >  # URCU_MB uses urcu.c but -DRCU_MB must be defined
> > > > -URCU_MB=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > > > +URCU_MB=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > > >  # URCU_SIGNAL uses urcu.c but -DRCU_SIGNAL must be defined
> > > > -URCU_SIGNAL=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > > > -URCU_BP=$(top_srcdir)/urcu-bp.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > > > -URCU_DEFER=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-defer.c $(top_srcdir)/urcu-pointer.c $(COMPAT)
> > > > +URCU_SIGNAL=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > > > +URCU_BP=$(top_srcdir)/urcu-bp.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > > > +URCU_DEFER=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-defer.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/urcu-call-rcu.c $(top_srcdir)/wfqueue.c $(COMPAT)
> > > >  
> > > >  URCU_LIB=$(top_builddir)/liburcu.la
> > > >  URCU_QSBR_LIB=$(top_builddir)/liburcu-qsbr.la
> > > >  URCU_MB_LIB=$(top_builddir)/liburcu-mb.la
> > > >  URCU_SIGNAL_LIB=$(top_builddir)/liburcu-signal.la
> > > >  URCU_BP_LIB=$(top_builddir)/liburcu-bp.la
> > > > +URCU_CALL_LIB=$(top_builddir)/liburcu-call.la
> > > >  WFQUEUE_LIB=$(top_builddir)/libwfqueue.la
> > > >  WFSTACK_LIB=$(top_builddir)/libwfstack.la
> > > >  RCULFQUEUE_LIB=$(top_builddir)/librculfqueue.la
> > > > @@ -95,23 +96,23 @@ test_perthreadlock_SOURCES = test_perthreadlock.c $(URCU_SIGNAL)
> > > >  
> > > >  rcutorture_urcu_SOURCES = urcutorture.c
> > > >  rcutorture_urcu_CFLAGS = -DTORTURE_URCU $(AM_CFLAGS)
> > > > -rcutorture_urcu_LDADD = $(URCU)
> > > > +rcutorture_urcu_LDADD = $(URCU) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> > > >  
> > > >  rcutorture_urcu_mb_SOURCES = urcutorture.c
> > > >  rcutorture_urcu_mb_CFLAGS = -DTORTURE_URCU_MB $(AM_CFLAGS)
> > > > -rcutorture_urcu_mb_LDADD = $(URCU_MB_LIB)
> > > > +rcutorture_urcu_mb_LDADD = $(URCU_MB_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> > > >  
> > > >  rcutorture_qsbr_SOURCES = urcutorture.c
> > > >  rcutorture_qsbr_CFLAGS = -DTORTURE_QSBR $(AM_CFLAGS)
> > > > -rcutorture_qsbr_LDADD = $(URCU_QSBR_LIB)
> > > > +rcutorture_qsbr_LDADD = $(URCU_QSBR_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> > > >  
> > > >  rcutorture_urcu_signal_SOURCES = urcutorture.c
> > > >  rcutorture_urcu_signal_CFLAGS = -DTORTURE_URCU_SIGNAL $(AM_CFLAGS)
> > > > -rcutorture_urcu_signal_LDADD = $(URCU_SIGNAL_LIB)
> > > > +rcutorture_urcu_signal_LDADD = $(URCU_SIGNAL_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> > > >  
> > > >  rcutorture_urcu_bp_SOURCES = urcutorture.c
> > > >  rcutorture_urcu_bp_CFLAGS = -DTORTURE_URCU_BP $(AM_CFLAGS)
> > > > -rcutorture_urcu_bp_LDADD = $(URCU_BP_LIB)
> > > > +rcutorture_urcu_bp_LDADD = $(URCU_BP_LIB) $(URCU_CALL_LIB) $(WFQUEUE_LIB)
> > > >  
> > > >  test_mutex_SOURCES = test_mutex.c $(URCU)
> > > >  
> > > > diff --git a/tests/rcutorture.h b/tests/rcutorture.h
> > > > index 4dac2f2..207d9f8 100644
> > > > --- a/tests/rcutorture.h
> > > > +++ b/tests/rcutorture.h
> > > > @@ -65,6 +65,8 @@
> > > >   * Test variables.
> > > >   */
> > > >  
> > > > +#include "../urcu-call-rcu.h"
> > > > +
> > > >  DEFINE_PER_THREAD(long long, n_reads_pt);
> > > >  DEFINE_PER_THREAD(long long, n_updates_pt);
> > > >  
> > > > @@ -296,10 +298,30 @@ void *rcu_read_stress_test(void *arg)
> > > >  	return (NULL);
> > > >  }
> > > >  
> > > > +static pthread_mutex_t call_rcu_test_mutex = PTHREAD_MUTEX_INITIALIZER;
> > > > +static pthread_cond_t call_rcu_test_cond = PTHREAD_COND_INITIALIZER;
> > > > +
> > > > +void rcu_update_stress_test_rcu(struct rcu_head *head)
> > > > +{
> > > > +	if (pthread_mutex_lock(&call_rcu_test_mutex) != 0) {
> > > > +		perror("pthread_mutex_lock");
> > > > +		exit(-1);
> > > > +	}
> > > > +	if (pthread_cond_signal(&call_rcu_test_cond) != 0) {
> > > > +		perror("pthread_cond_signal");
> > > > +		exit(-1);
> > > > +	}
> > > > +	if (pthread_mutex_unlock(&call_rcu_test_mutex) != 0) {
> > > > +		perror("pthread_mutex_unlock");
> > > > +		exit(-1);
> > > > +	}
> > > > +}
> > > > +
> > > >  void *rcu_update_stress_test(void *arg)
> > > >  {
> > > >  	int i;
> > > >  	struct rcu_stress *p;
> > > > +	struct rcu_head rh;
> > > >  
> > > >  	while (goflag == GOFLAG_INIT)
> > > >  		poll(NULL, 0, 1);
> > > > @@ -317,7 +339,24 @@ void *rcu_update_stress_test(void *arg)
> > > >  		for (i = 0; i < RCU_STRESS_PIPE_LEN; i++)
> > > >  			if (i != rcu_stress_idx)
> > > >  				rcu_stress_array[i].pipe_count++;
> > > > -		synchronize_rcu();
> > > > +		if (n_updates & 0x1)
> > > > +			synchronize_rcu();
> > > > +		else {
> > > > +			if (pthread_mutex_lock(&call_rcu_test_mutex) != 0) {
> > > > +				perror("pthread_mutex_lock");
> > > > +				exit(-1);
> > > > +			}
> > > > +			call_rcu(&rh, rcu_update_stress_test_rcu);
> > > > +			if (pthread_cond_wait(&call_rcu_test_cond,
> > > > +					      &call_rcu_test_mutex) != 0) {
> > > > +				perror("pthread_cond_wait");
> > > > +				exit(-1);
> > > > +			}
> > > > +			if (pthread_mutex_unlock(&call_rcu_test_mutex) != 0) {
> > > > +				perror("pthread_mutex_unlock");
> > > > +				exit(-1);
> > > > +			}
> > > > +		}
> > > >  		n_updates++;
> > > >  	}
> > > >  	return NULL;
> > > > diff --git a/urcu-call-rcu.c b/urcu-call-rcu.c
> > > > new file mode 100644
> > > > index 0000000..d59a2d7
> > > > --- /dev/null
> > > > +++ b/urcu-call-rcu.c
> > > > @@ -0,0 +1,405 @@
> > > > +/*
> > > > + * urcu-call-rcu.c
> > > > + *
> > > > + * Userspace RCU library - batch memory reclamation with kernel API
> > > > + *
> > > > + * Copyright (c) 2010 Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> > > > + *
> > > > + * This library is free software; you can redistribute it and/or
> > > > + * modify it under the terms of the GNU Lesser General Public
> > > > + * License as published by the Free Software Foundation; either
> > > > + * version 2.1 of the License, or (at your option) any later version.
> > > > + *
> > > > + * This library is distributed in the hope that it will be useful,
> > > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > > + * Lesser General Public License for more details.
> > > > + *
> > > > + * You should have received a copy of the GNU Lesser General Public
> > > > + * License along with this library; if not, write to the Free Software
> > > > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> > > > + */
> > > > +
> > > > +#include <stdio.h>
> > > > +#include <pthread.h>
> > > > +#include <signal.h>
> > > > +#include <assert.h>
> > > > +#include <stdlib.h>
> > > > +#include <string.h>
> > > > +#include <errno.h>
> > > > +#include <poll.h>
> > > > +#include <sys/time.h>
> > > > +#include <syscall.h>
> > > > +#include <unistd.h>
> > > > +
> > > > +#include "config.h"
> > > > +#include "urcu/wfqueue.h"
> > > > +#include "urcu-call-rcu.h"
> > > > +#include "urcu-pointer.h"
> > > > +
> > > > +/* Data structure that identifies a call_rcu thread. */
> > > > +
> > > > +struct call_rcu_data {
> > > > +	struct cds_wfq_queue cbs;
> > > > +	unsigned long flags;
> > > > +	pthread_mutex_t mtx;
> > > > +	pthread_cond_t cond;
> > > > +	unsigned long qlen;
> > > > +	pthread_t tid;
> > > > +} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
> > > > +
> > > > +/* Link a thread using call_rcu() to its call_rcu thread. */
> > > > +
> > > > +static __thread struct call_rcu_data *thread_call_rcu_data;
> > > > +
> > > > +/* Guard call_rcu thread creation. */
> > > > +
> > > > +static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
> > > > +
> > > > +/* If a given thread does not have its own call_rcu thread, this is default. */
> > > > +
> > > > +static struct call_rcu_data *default_call_rcu_data;
> > > > +
> > > > +extern void synchronize_rcu(void);
> > > > +
> > > > +/*
> > > > + * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
> > > > + * available, then we can have call_rcu threads assigned to individual
> > > > + * CPUs rather than only to specific threads.
> > > > + */
> > > > +
> > > > +#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
> > > > +
> > > > +/*
> > > > + * Pointer to array of pointers to per-CPU call_rcu_data structures
> > > > + * and # CPUs.
> > > > + */
> > > > +
> > > > +static struct call_rcu_data **per_cpu_call_rcu_data;
> > > > +static long maxcpus;
> > > > +
> > > > +/* Allocate the array if it has not already been allocated. */
> > > > +
> > > > +static void alloc_cpu_call_rcu_data(void)
> > > > +{
> > > > +	struct call_rcu_data **p;
> > > > +
> > > > +	if (maxcpus != 0)
> > > > +		return;
> > > > +	maxcpus = sysconf(_SC_NPROCESSORS_CONF);
> > > 
> > > I noticed an odd sysconf behavior inside a chroot jail where /proc was not
> > > mounted: it returns 1 single CPU for _SC_NPROCESSORS_CONF, which would be
> > > catastrophic here because the array would be too small to match the index
> > > returned by sched_getcpu. Any thought on how we should deal with this ?
> > > Maybe doing an extra value sanity check in our own wrapper over sched_getcpu
> > > would be appropriate ?
> > 
> > Good catch, we do need a range check in get_call_rcu_data(), which I
> > I have added.  That is the only sched_getcpu() in the call_rcu() code,
> > so that should cover it.  If the CPU is out of range, we fall back to
> > the default global CPU.
> 
> I'm wondering if it is OK for a library to silently accept that we're falling
> back on global queue rather than per-cpu if the range is incorrect and when we
> fail to allocate memory. See below,
> 
> > 
> > > > +	if (maxcpus == -1)
> > > > +		return;
> > > > +	p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
> > > 
> > > Shouldn't we yell or something if p is null ? :-)
> > 
> > If p is NULL, it will just force use of the global call_rcu() thread.
> > The data for this thread is static, so always there.
> > 
> > But what form of yelling did you have in mind?
> 
> e.g.
> 
> if (!p)
>   fprintf(stderr, "[error] liburcu: unable to allocate per_cpu data\n");

OK, I can do that.

> > > > +	if (p != NULL)
> > > > +		memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
> > > > +}
> > > > +
> > > > +#else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
> > > > +
> > > > +static const struct call_rcu_data **per_cpu_call_rcu_data = NULL;
> > > > +static const long maxcpus = -1;
> > > > +
> > > > +static void alloc_cpu_call_rcu_data(void)
> > > > +{
> > > > +}
> > > > +
> > > > +static int sched_getcpu(void)
> > > > +{
> > > > +	return -1;
> > > > +}
> > > > +
> > > > +#endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
> > > > +
> > > > +/* Acquire the specified pthread mutex. */
> > > > +
> > > > +static void call_rcu_lock(pthread_mutex_t *pmp)
> > > > +{
> > > > +	if (pthread_mutex_lock(pmp) != 0) {
> > > > +		perror("pthread_mutex_lock");
> > > > +		exit(-1);
> > > > +	}
> > > > +}
> > > > +
> > > > +/* Release the specified pthread mutex. */
> > > > +
> > > > +static void call_rcu_unlock(pthread_mutex_t *pmp)
> > > > +{
> > > > +	if (pthread_mutex_unlock(pmp) != 0) {
> > > > +		perror("pthread_mutex_unlock");
> > > > +		exit(-1);
> > > > +	}
> > > > +}
> > > > +
> > > > +/* This is the code run by each call_rcu thread. */
> > > > +
> > > > +static void *call_rcu_thread(void *arg)
> > > > +{
> > > > +	unsigned long cbcount;
> > > > +	struct cds_wfq_node *cbs;
> > > > +	struct cds_wfq_node **cbs_tail;
> > > > +	struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
> > > > +	struct rcu_head *rhp;
> > > > +
> > > > +	thread_call_rcu_data = crdp;
> > > > +	for (;;) {
> > > > +		if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
> > > > +			while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
> > > > +				poll(NULL, 0, 1);
> > > > +			_CMM_STORE_SHARED(crdp->cbs.head, NULL);
> > > > +			cbs_tail = (struct cds_wfq_node **)
> > > > +				uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
> > > > +			synchronize_rcu();
> > > > +			cbcount = 0;
> > > > +			do {
> > > > +				while (cbs->next == NULL &&
> > > > +				       &cbs->next != cbs_tail)
> > > > +				       	poll(NULL, 0, 1);
> > > > +				if (cbs == &crdp->cbs.dummy) {
> > > > +					cbs = cbs->next;
> > > > +					continue;
> > > > +				}
> > > > +				rhp = (struct rcu_head *)cbs;
> > > > +				cbs = cbs->next;
> > > > +				rhp->func(rhp);
> > > > +				cbcount++;
> > > > +			} while (cbs != NULL);
> > > > +			uatomic_sub(&crdp->qlen, cbcount);
> > > > +		}
> > > > +		if (crdp->flags & URCU_CALL_RCU_RT)
> > > > +			poll(NULL, 0, 10);
> > > > +		else {
> > > > +			call_rcu_lock(&crdp->mtx);
> > > > +			_CMM_STORE_SHARED(crdp->flags,
> > > > +				     crdp->flags & ~URCU_CALL_RCU_RUNNING);
> > > > +			if (&cbs->next != crdp->cbs.tail &&
> > > > +			    pthread_cond_wait(&crdp->cond, &crdp->mtx) != 0) {
> > > > +				perror("pthread_cond_wait");
> > > > +				exit(-1);
> > > > +			}
> > > > +			_CMM_STORE_SHARED(crdp->flags,
> > > > +				     crdp->flags | URCU_CALL_RCU_RUNNING);
> > > > +			poll(NULL, 0, 10);
> > > > +			call_rcu_unlock(&crdp->mtx);
> > > > +		}
> > > > +	}
> > > > +	return NULL;  /* NOTREACHED */
> > > 
> > > I'm not sure how this thread is supposed to clean up properly at process exit ?
> > 
> > Given that all it has is in-memory data structures, when exit() makes
> > the address space vanish, that will implicity clean things up for this
> > thread.
> > 
> > Or am I missing your point?
> 
> Well, technically, we should free all memory that has been allocated by malloc.
> Otherwise, memory leak detection tools like valgrind will not be happy at all.
> So relying on process exit to free memory seems a bit inelegant.

I am having a very hard time believing that applications free() all
the memory that they malloc()...

I suppose that I could put in an atexit call, but then we get hammered
when later atexit calls try to use RCU.  :-(

> > > > +}
> > > > +
> > > > +/*
> > > > + * Create both a call_rcu thread and the corresponding call_rcu_data
> > > > + * structure, linking the structure in as specified.
> > > > + */
> > > > +
> > > > +void call_rcu_data_init(struct call_rcu_data **crdpp, unsigned long flags)
> > > > +{
> > > > +	struct call_rcu_data *crdp;
> > > > +
> > > > +	crdp = malloc(sizeof(*crdp));
> > > > +	if (crdp == NULL) {
> > > > +		fprintf(stderr, "Out of memory.\n");
> > > > +		exit(-1);
> > > > +	}
> > > > +	memset(crdp, '\0', sizeof(*crdp));
> > > > +	cds_wfq_init(&crdp->cbs);
> > > > +	crdp->qlen = 0;
> > > > +	if (pthread_mutex_init(&crdp->mtx, NULL) != 0) {
> > > > +		perror("pthread_mutex_init");
> > > > +		exit(-1);
> > > > +	}
> > > > +	if (pthread_cond_init(&crdp->cond, NULL) != 0) {
> > > > +		perror("pthread_cond_init");
> > > > +		exit(-1);
> > > > +	}
> > > > +	crdp->flags = flags | URCU_CALL_RCU_RUNNING;
> > > > +	cmm_smp_mb();  /* Structure initialized before pointer is planted. */
> > > > +	*crdpp = crdp;
> > > > +	if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
> > > > +		perror("pthread_create");
> > > > +		exit(-1);
> > > > +	}
> > > > +}
> > > > +
> > > > +/*
> > > > + * Return a pointer to the call_rcu_data structure for the specified
> > > > + * CPU, returning NULL if there is none.  We cannot automnatically
> > > 
> > > automnatically -> automatically
> > 
> > Good eyes, fixed.
> > 
> > But wouldn't you really prefer automaniacally?  ;-)
> 
> lol :)
> 
> > 
> > > > + * created it because the platform we are running on might not define
> > > > + * sched_getcpu().
> > > > + */
> > > > +
> > > > +struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
> > > > +{
> > > > +	if (per_cpu_call_rcu_data == NULL)
> > > > +		return NULL;
> > > > +	if (cpu < 0 || maxcpus <= cpu)
> > > > +		return NULL;
> > > 
> > > Ah! I think this is where is would make sense to validate that "cpu" is not out
> > > of bounds. If it is, then we could fallback on the default call_rcu thread, or
> > > yell about lack of /proc.
> > 
> > You lost me here -- we are validating that the "cpu" is not out of bounds
> > with respect to the array bounds.  The caller sees the NULL pointer and
> > acts accordingly.
> > 
> > I did need to add a check to get_call_rcu_data() down below, which I did.
> 
> Well my point is that letting the library silently take a slower fallback
> without complaining as a result of an error situation (-ENOMEM, /proc
> unavailable) is, IMHO, heading towards a disaster. We want the library to print
> an error message, at least once, when it find about such problematic situations.
> 
> In this specific case, if "cpu > maxcpus", something _is_ wrong, so we should
> print an appropriate error message (and fallback on the slower default callback
> queue of course).

OK, easy enough to try, and should cause problems in most cases.  I will
include this in my next patch.

> > > > +	return per_cpu_call_rcu_data[cpu];
> > > > +}
> > > > +
> > > > +/*
> > > > + * Return the tid corresponding to the call_rcu thread whose
> > > > + * call_rcu_data structure is specified.
> > > > + */
> > > > +
> > > > +pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
> > > > +{
> > > > +	return crdp->tid;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Create a call_rcu_data structure (with thread) and return a pointer.
> > > > + */
> > > > +
> > > > +struct call_rcu_data *create_call_rcu_data(unsigned long flags)
> > > > +{
> > > > +	struct call_rcu_data *crdp;
> > > > +
> > > > +	call_rcu_data_init(&crdp, flags);
> > > > +	return crdp;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Set the specified CPU to use the specified call_rcu_data structure.
> > > > + */
> > > > +
> > > > +int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
> > > > +{
> > > > +	call_rcu_lock(&call_rcu_mutex);
> > > > +	alloc_cpu_call_rcu_data();
> > > > +	call_rcu_unlock(&call_rcu_mutex);
> > > > +	if (cpu < 0 || maxcpus <= cpu || per_cpu_call_rcu_data == NULL)
> > > > +		return 0;
> > > > +	per_cpu_call_rcu_data[cpu] = crdp;
> > > 
> > > another point where we chould validate that cpu is not out of bound.
> > 
> > The validation is already there: "cpu < 0 || maxcpus <= cpu".
> > 
> > What am I missing here?
> 
> Same as the previous one: if (cpu > maxcpus), we know that something is wrong.
> I'm OK with returning 0 and using a fallback, but only after printing an error
> message in this case.
> 
> Also, I'm wondering if we should reverse the return logic here: usually, other
> functions in this library return 0 on success, and -ESOMETHING on error.

OK, in the "per_cpu_call_rcu_data == NULL", -ENOMEM is a no-brainer.
For the CPU being out of bounds, I guess the right answer is -EINVAL.

> > > > +	return 1;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Return a pointer to the default call_rcu_data structure, creating
> > > > + * one if need be.  Because we never free call_rcu_data structures,
> > > > + * we don't need to be in an RCU read-side critical section.
> > > > + */
> > > > +
> > > > +struct call_rcu_data *get_default_call_rcu_data(void)
> > > > +{
> > > > +	if (default_call_rcu_data != NULL)
> > > > +		return rcu_dereference(default_call_rcu_data);
> > > > +	call_rcu_lock(&call_rcu_mutex);
> > > > +	if (default_call_rcu_data != NULL) {
> > > > +		call_rcu_unlock(&call_rcu_mutex);
> > > > +		return default_call_rcu_data;
> > > > +	}
> > > > +	call_rcu_data_init(&default_call_rcu_data, 0);
> > > > +	call_rcu_unlock(&call_rcu_mutex);
> > > > +	return default_call_rcu_data;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Return the call_rcu_data structure that applies to the currently
> > > > + * running thread.  Any call_rcu_data structure assigned specifically
> > > > + * to this thread has first priority, followed by any call_rcu_data
> > > > + * structure assigned to the CPU on which the thread is running,
> > > > + * followed by the default call_rcu_data structure.  If there is not
> > > > + * yet a default call_rcu_data structure, one will be created.
> > > > + */
> > > > +struct call_rcu_data *get_call_rcu_data(void)
> > > > +{
> > > > +	int curcpu;
> > > > +
> > > > +	if (thread_call_rcu_data != NULL)
> > > > +		return thread_call_rcu_data;
> > > > +	curcpu = sched_getcpu();
> > 
> > Now -here- we need validation.  The following "if" becomes:
> > 
> > 	if (curcpu >= 0 && maxcpus > curcpu &&
> > 	    per_cpu_call_rcu_data != NULL &&
> > 	    per_cpu_call_rcu_data[curcpu] != NULL)
> > 	    	return per_cpu_call_rcu_data[curcpu];
> > 
> > > > +	if (per_cpu_call_rcu_data != NULL &&
> > > > +	    per_cpu_call_rcu_data[curcpu] != NULL)
> > > 
> > > Another array bounds validation here ?
> > 
> > Yep, see above.
> 
> I'd also be tempted to print an error message (once) for the specific case where
> cpu > maxcpus.

Indeed, printing more than once seems like overkill.  I will check on
the feasibility of propagating errno all the way back out to the caller,
might be better.  Though wouldn't that instead be an assignment to errno
followed by a non-zero return value?

> > > > +	    	return per_cpu_call_rcu_data[curcpu];
> > > > +	return get_default_call_rcu_data();
> > > > +}
> > > > +
> > > > +/*
> > > > + * Return a pointer to this task's call_rcu_data if there is one.
> > > > + */
> > > > +
> > > > +struct call_rcu_data *get_thread_call_rcu_data(void)
> > > > +{
> > > > +	return thread_call_rcu_data;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Set this task's call_rcu_data structure as specified, regardless
> > > > + * of whether or not this task already had one.  (This allows switching
> > > > + * to and from real-time call_rcu threads, for example.)
> > > > + */
> > > > +
> > > > +void set_thread_call_rcu_data(struct call_rcu_data *crdp)
> > > > +{
> > > > +	thread_call_rcu_data = crdp;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Create a separate call_rcu thread for each CPU.  This does not
> > > > + * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
> > > > + * function if you want that behavior.
> > > > + */
> > > > +
> > > > +int create_all_cpu_call_rcu_data(unsigned long flags)
> > > > +{
> > > > +	int i;
> > > > +	struct call_rcu_data *crdp;
> > > > +
> > > > +	call_rcu_lock(&call_rcu_mutex);
> > > > +	alloc_cpu_call_rcu_data();
> > > > +	call_rcu_unlock(&call_rcu_mutex);
> > > > +	if (maxcpus == -1 || per_cpu_call_rcu_data == NULL)
> > > > +		return 0;
> > > > +	for (i = 0; i < maxcpus; i++) {
> > > > +		call_rcu_lock(&call_rcu_mutex);
> > > > +		if (get_cpu_call_rcu_data(i)) {
> > > > +			call_rcu_unlock(&call_rcu_mutex);
> > > > +			continue;
> > > > +		}
> > > > +		crdp = create_call_rcu_data(flags);
> > > 
> > > Hrm, just so we're clear: on a 8-way system with a kernel supporting up to 32
> > > possible cpus, this would create 32 threads per application. Is it really what
> > > we want ?
> > 
> > Only if the application invokes create_all_cpu_call_rcu_data().
> > If an application uses call_rcu() only rarely, then it should avoid
> > calling create_all_cpu_call_rcu_data(), instead relying on the single
> > default call_rcu() thread.
> > 
> > > For the non-RT case, we might want to investigate using sysconf get "online"
> > > cpus, and fixup dynamically within call_rcu() if we discover that
> > > 
> > > 1) per-cpu rcu_data should be available
> > > 2) some data within our per-cpu rcu_data tells us that it has not been allocated
> > > 
> > > So we could allocate the per-cpu rcu_data array for the number of possible cpus
> > > on the system, but only allocate more expensive ressources (e.g. create threads)
> > > for the number of online cpus, and dynamically spawn threads if needed.
> > > 
> > > We could leave the code as is for the RT case (allocate threads for each
> > > possible cpus). Thoughts ?
> > 
> > I am for keeping it simple to begin with.  On most modern systems,
> > I bet that the extra few tens of threads is not going to be a big deal.
> 
> Simple to begin with is good enough for me, and as you say, the default is the
> global queue.

Sounds good!

> > > > +		if (crdp == NULL) {
> > > > +			call_rcu_unlock(&call_rcu_mutex);
> > > > +			return 0;
> > > > +		}
> > > > +		if (!set_cpu_call_rcu_data(i, crdp)) {
> > > > +			call_rcu_unlock(&call_rcu_mutex);
> > > > +			return 0; /* should not happen, but... */
> > > > +		}
> > > > +		call_rcu_unlock(&call_rcu_mutex);
> > > > +	}
> > > > +	return 1;
> > > > +}
> > > > +
> > > > +/*
> > > > + * Schedule a function to be invoked after a following grace period.
> > > > + * This is the only function that must be called -- the others are
> > > > + * only present to allow applications to tune their use of RCU for
> > > > + * maximum performance.
> > > > + *
> > > > + * Note that unless a call_rcu thread has not already been created,
> > > > + * the first invocation of call_rcu() will create one.  So, if you
> > > > + * need the first invocation of call_rcu() to be fast, make sure
> > > > + * to create a call_rcu thread first.  One way to accomplish this is
> > > > + * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
> > > > + */
> > > > +
> > > > +void call_rcu(struct rcu_head *head,
> > > > +	      void (*func)(struct rcu_head *head))
> > > > +{
> > > > +	struct call_rcu_data *crdp;
> > > > +
> > > > +	cds_wfq_node_init(&head->next);
> > > > +	head->func = func;
> > > > +	crdp = get_call_rcu_data();
> > > > +	cds_wfq_enqueue(&crdp->cbs, &head->next);
> > > > +	uatomic_inc(&crdp->qlen);
> > > > +	if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT)) {
> > > > +		call_rcu_lock(&crdp->mtx);
> > > > +		if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RUNNING)) {
> > > > +			if (pthread_cond_signal(&crdp->cond) != 0) {
> > > > +				perror("pthread_cond_signal");
> > > > +				exit(-1);
> > > > +			}
> > > > +		}
> > > > +		call_rcu_unlock(&crdp->mtx);
> > > > +	}
> > > > +}
> > > > diff --git a/urcu-call-rcu.h b/urcu-call-rcu.h
> > > > new file mode 100644
> > > > index 0000000..b390b7e
> > > > --- /dev/null
> > > > +++ b/urcu-call-rcu.h
> > > > @@ -0,0 +1,80 @@
> > > > +#ifndef _URCU_CALL_RCU_H
> > > > +#define _URCU_CALL_RCU_H
> > > > +
> > > > +/*
> > > > + * urcu-defer.h
> > > 
> > > urcu-call-rcu.h
> > 
> > Good catch, fixed.
> > 
> > > > + *
> > > > + * Userspace RCU header - deferred execution
> > > > + *
> > > > + * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > > > + * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
> > > > + *
> > > > + * LGPL-compatible code should include this header with :
> > > > + *
> > > > + * #define _LGPL_SOURCE
> > > > + * #include <urcu-defer.h>
> > > > + *
> > > > + * This library is free software; you can redistribute it and/or
> > > > + * modify it under the terms of the GNU Lesser General Public
> > > > + * License as published by the Free Software Foundation; either
> > > > + * version 2.1 of the License, or (at your option) any later version.
> > > > + *
> > > > + * This library is distributed in the hope that it will be useful,
> > > > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > > > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > > > + * Lesser General Public License for more details.
> > > > + *
> > > > + * You should have received a copy of the GNU Lesser General Public
> > > > + * License along with this library; if not, write to the Free Software
> > > > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> > > > + */
> > > > +
> > > > +#include <stdlib.h>
> > > > +#include <pthread.h>
> > > > +
> > > > +#include "urcu/wfqueue.h"
> > > 
> > > should this header be between < > instead ?
> > 
> > No idea, I was just copying the other examples using double quotes.
> > 
> > I fixed this one to use angle brackets, and leave the others to you.
> 
> Hopefully I'm not missing something I should myself remember. :-/ This might
> become important when we choose to lookup for headers in the urcu tree before
> the same header installed in the system.

OK, let me know if I need to change it back.

> > > > +
> > > > +#ifdef __cplusplus
> > > > +extern "C" {
> > > > +#endif
> > > > +
> > > > +/* Note that struct call_rcu_data is opaque to callers. */
> > > > +
> > > > +struct call_rcu_data;
> > > > +
> > > > +/* Flag values. */
> > > > +
> > > > +#define URCU_CALL_RCU_RT	0x1
> > > > +#define URCU_CALL_RCU_RUNNING	0x2
> > > > +
> > > > +/*
> > > > + * The rcu_head data structure is placed in the structure to be freed
> > > > + * via call_rcu().
> > > > + */
> > > > +
> > > > +struct rcu_head {
> > > > +	struct cds_wfq_node next;
> > > > +	void (*func)(struct rcu_head *head);
> > > > +};
> > > > +
> > > > +/*
> > > > + * Exported functions
> > > > + */
> > > > +void call_rcu_data_init(struct call_rcu_data **crdpp, unsigned long flags);
> > > > +struct call_rcu_data *get_cpu_call_rcu_data(int cpu);
> > > > +pthread_t get_call_rcu_thread(struct call_rcu_data *crdp);
> > > > +struct call_rcu_data *create_call_rcu_data(unsigned long flags);
> > > > +int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp);
> > > > +struct call_rcu_data *get_default_call_rcu_data(void);
> > > > +struct call_rcu_data *get_call_rcu_data(void);
> > > > +struct call_rcu_data *get_thread_call_rcu_data(void);
> > > > +void set_thread_call_rcu_data(struct call_rcu_data *crdp);
> > > > +int create_all_cpu_call_rcu_data(unsigned long flags);
> > > > +void call_rcu(struct rcu_head *head,
> > > > +	      void (*func)(struct rcu_head *head));
> > > > +
> > > > +#ifdef __cplusplus 
> > > > +}
> > > > +#endif
> > > > +
> > > > +#endif /* _URCU_CALL_RCU_H */
> > > > diff --git a/urcu-defer.h b/urcu-defer.h
> > > > index e161616..a64c75c 100644
> > > > --- a/urcu-defer.h
> > > > +++ b/urcu-defer.h
> > > > @@ -53,14 +53,6 @@ extern "C" {
> > > >  extern void defer_rcu(void (*fct)(void *p), void *p);
> > > >  
> > > >  /*
> > > > - * call_rcu will eventually be implemented with an API similar to the Linux
> > > > - * kernel call_rcu(), which will allow its use within RCU read-side C.S.
> > > > - * Generate an error if used for now.
> > > > - */
> > > > -
> > > > -#define call_rcu	__error_call_rcu_not_implemented_please_use_defer_rcu
> > > > -
> > > > -/*
> > > >   * Thread registration for reclamation.
> > > >   */
> > > >  extern void rcu_defer_register_thread(void);
> > > > diff --git a/urcu/wfqueue-static.h b/urcu/wfqueue-static.h
> > > > index 30d6e96..a989f28 100644
> > > > --- a/urcu/wfqueue-static.h
> > > > +++ b/urcu/wfqueue-static.h
> > > > @@ -47,11 +47,17 @@ extern "C" {
> > > >  #define WFQ_ADAPT_ATTEMPTS		10	/* Retry if being set */
> > > >  #define WFQ_WAIT			10	/* Wait 10 ms if being set */
> > > >  
> > > > +#ifdef _LGPL_SOURCE
> > > > +static inline
> > > > +#endif /* #ifdef _LGPL_SOURCE */
> > > 
> > > We should actually declare all these as "static inline" in every case, and
> > > create a little .c file in the urcu root to contain the wrapper stub library
> > > apps could link to. This would follow the same layout I've used for all the
> > > other code.
> > 
> > Let me make sure I understand what you are looking for here...
> > 
> > You want a urcu-call-rcu-static.h, which will contain the current
> > contents of urcu-call-rcu.c, but with all exported functions having
> > their names prefixed by "_".  Then the new urcu-call-rcu.c has one
> > wrapper function per exported function, correct?
> 
> Yes, and urcu-call.h defines wrapper macros for the _LGPL_SOURCE case. urcu.h,
> urcu-static.h and urcu.c are very good examples of this.

OK, will follow the urcu case.

							Thanx, Paul

> Thanks Paul !
> 
> Mathieu
> 
> > 
> > 							Thanx, Paul
> > 
> > > Thanks,
> > > 
> > > Mathieu
> > > 
> > > >  void _cds_wfq_node_init(struct cds_wfq_node *node)
> > > >  {
> > > >  	node->next = NULL;
> > > >  }
> > > >  
> > > > +#ifdef _LGPL_SOURCE
> > > > +static inline
> > > > +#endif /* #ifdef _LGPL_SOURCE */
> > > >  void _cds_wfq_init(struct cds_wfq_queue *q)
> > > >  {
> > > >  	int ret;
> > > > @@ -64,6 +70,9 @@ void _cds_wfq_init(struct cds_wfq_queue *q)
> > > >  	assert(!ret);
> > > >  }
> > > >  
> > > > +#ifdef _LGPL_SOURCE
> > > > +static inline
> > > > +#endif /* #ifdef _LGPL_SOURCE */
> > > >  void _cds_wfq_enqueue(struct cds_wfq_queue *q, struct cds_wfq_node *node)
> > > >  {
> > > >  	struct cds_wfq_node **old_tail;
> > > > @@ -90,6 +99,9 @@ void _cds_wfq_enqueue(struct cds_wfq_queue *q, struct cds_wfq_node *node)
> > > >   * thread to be scheduled. The queue appears empty until tail->next is set by
> > > >   * enqueue.
> > > >   */
> > > > +#ifdef _LGPL_SOURCE
> > > > +static inline
> > > > +#endif /* #ifdef _LGPL_SOURCE */
> > > >  struct cds_wfq_node *
> > > >  ___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> > > >  {
> > > > @@ -128,6 +140,9 @@ ___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> > > >  	return node;
> > > >  }
> > > >  
> > > > +#ifdef _LGPL_SOURCE
> > > > +static inline
> > > > +#endif /* #ifdef _LGPL_SOURCE */
> > > >  struct cds_wfq_node *
> > > >  _cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> > > >  {
> > > 
> > > -- 
> > > Mathieu Desnoyers
> > > Operating System Efficiency R&D Consultant
> > > EfficiOS Inc.
> > > http://www.efficios.com
> > > 
> > > _______________________________________________
> > > rp mailing list
> > > rp at svcs.cs.pdx.edu
> > > http://svcs.cs.pdx.edu/mailman/listinfo/rp
> 
> -- 
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
> 
> _______________________________________________
> rp mailing list
> rp at svcs.cs.pdx.edu
> http://svcs.cs.pdx.edu/mailman/listinfo/rp