[lttng-dev] [RFC PATCH] Userspace RCU library internal error handling
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Thu Jun 21 15:14:51 EDT 2012
* Mathieu Desnoyers (mathieu.desnoyers at efficios.com) wrote:
> * Josh Triplett (josh at joshtriplett.org) wrote:
> > On Thu, Jun 21, 2012 at 12:41:13PM -0400, Mathieu Desnoyers wrote:
> > > Currently, liburcu calls "exit(-1)" upon internal consistency error.
> > > This is not pretty, and usually frowned upon in libraries.
> >
> > Agreed.
> >
> > > One example of failure path where we use this is if pthread_mutex_lock()
> > > would happen to fail within synchronize_rcu(). Clearly, this should
> > > _never_ happen: it would typically be triggered only by memory
> > > corruption (or other terrible things like that). That being said, we
> > > clearly don't want to make "synchronize_rcu()" return errors like that
> > > to the application, because it would complexify the application error
> > > handling needlessly.
> >
> > I think you can safely ignore any error conditions you know you can't
> > trigger. pthread_mutex_lock can only return an error under two
> > conditions: an uninitialized mutex, or an error-checking mutex already
> > locked by the current thread. Neither of those can happen in this case.
> > Given that, I'd suggest either calling pthread_mutex_lock and ignoring
> > any possibility of error, or adding an assert.
> >
> > > So instead of calling exit(-1), one possibility would be to do something
> > > like this:
> > >
> > > #include <signal.h>
> > > #include <pthread.h>
> > > #include <stdio.h>
> > >
> > > #define urcu_die(fmt, ...) \
> > > do { \
> > > fprintf(stderr, fmt, ##__VA_ARGS__); \
> > > (void) pthread_kill(pthread_self(), SIGBUS); \
> > > } while (0)
> > >
> > > and call urcu_die(); in those "unrecoverable error" cases, instead of
> > > calling exit(-1). Therefore, if an application chooses to trap those
> > > signals, it can, which is otherwise not possible with a direct call to
> > > exit().
> >
> > It looks like you want to use signals as a kind of exception mechanism,
> > to allow the application to clean up (though not to recover). assert
> > seems much clearer to me for "this can't happen" cases, and assert also
> > generates a signal that the application can catch and clean up.
>
> Within discussions with other LTTng developers, we considered the the
> assert, but the thought that this case might be silently ignored on
> production systems (which compile with assertions disabled) makes me
> uncomfortable. This is why I would prefer a SIGBUS to an assertion.
>
> Using assert() would be similar to turning the Linux kernel BUG_ON()
> mechanism into no-ops on production systems because "it should never
> happen" (tm) ;-)
Here is the patch for comments.
---
diff --git a/Makefile.am b/Makefile.am
index 933e538..2396fcf 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -22,6 +22,8 @@ nobase_dist_include_HEADERS = urcu/compiler.h urcu/hlist.h urcu/list.h \
urcu/tls-compat.h
nobase_nodist_include_HEADERS = urcu/arch.h urcu/uatomic.h urcu/config.h
+dist_noinst_HEADERS = urcu-die.h
+
EXTRA_DIST = $(top_srcdir)/urcu/arch/*.h $(top_srcdir)/urcu/uatomic/*.h \
gpl-2.0.txt lgpl-2.1.txt lgpl-relicensing.txt \
LICENSE compat_arch_x86.c \
diff --git a/urcu-bp.c b/urcu-bp.c
index 67eae07..b9c89d8 100644
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -42,6 +42,8 @@
#include "urcu-pointer.h"
#include "urcu/tls-compat.h"
+#include "urcu-die.h"
+
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#undef _LGPL_SOURCE
#include "urcu-bp.h"
@@ -142,17 +144,12 @@ static void mutex_lock(pthread_mutex_t *mutex)
#ifndef DISTRUST_SIGNALS_EXTREME
ret = pthread_mutex_lock(mutex);
- if (ret) {
- perror("Error in pthread mutex lock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
while ((ret = pthread_mutex_trylock(mutex)) != 0) {
- if (ret != EBUSY && ret != EINTR) {
- printf("ret = %d, errno = %d\n", ret, errno);
- perror("Error in pthread mutex lock");
- exit(-1);
- }
+ if (ret != EBUSY && ret != EINTR)
+ urcu_die(ret);
poll(NULL,0,10);
}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
@@ -163,10 +160,8 @@ static void mutex_unlock(pthread_mutex_t *mutex)
int ret;
ret = pthread_mutex_unlock(mutex);
- if (ret) {
- perror("Error in pthread mutex unlock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
}
void update_counter_and_wait(void)
diff --git a/urcu-die.h b/urcu-die.h
new file mode 100644
index 0000000..e925d74
--- /dev/null
+++ b/urcu-die.h
@@ -0,0 +1,38 @@
+#ifndef _URCU_DIE_H
+#define _URCU_DIE_H
+
+/*
+ * urcu-die.h
+ *
+ * Userspace RCU library unrecoverable error handling
+ *
+ * Copyright (c) 2012 Mathieu Desnoyers <mathieu.desnoyers at efficios.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 <signal.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <string.h>
+
+#define urcu_die(cause) \
+do { \
+ fprintf(stderr, "(" __FILE__ ":%s@%u) Unrecoverable error: %s\n", \
+ __func__, __LINE__, strerror(cause)); \
+ (void) pthread_kill(pthread_self(), SIGBUS); \
+} while (0)
+
+#endif /* _URCU_DIE_H */
diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index b20d564..d3a6849 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -42,6 +42,8 @@
#include "urcu-pointer.h"
#include "urcu/tls-compat.h"
+#include "urcu-die.h"
+
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#undef _LGPL_SOURCE
#include "urcu-qsbr.h"
@@ -82,17 +84,12 @@ static void mutex_lock(pthread_mutex_t *mutex)
#ifndef DISTRUST_SIGNALS_EXTREME
ret = pthread_mutex_lock(mutex);
- if (ret) {
- perror("Error in pthread mutex lock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
while ((ret = pthread_mutex_trylock(mutex)) != 0) {
- if (ret != EBUSY && ret != EINTR) {
- printf("ret = %d, errno = %d\n", ret, errno);
- perror("Error in pthread mutex lock");
- exit(-1);
- }
+ if (ret != EBUSY && ret != EINTR)
+ urcu_die(ret);
poll(NULL,0,10);
}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
@@ -103,10 +100,8 @@ static void mutex_unlock(pthread_mutex_t *mutex)
int ret;
ret = pthread_mutex_unlock(mutex);
- if (ret) {
- perror("Error in pthread mutex unlock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
}
/*
diff --git a/urcu.c b/urcu.c
index 5fb4db8..a5178c0 100644
--- a/urcu.c
+++ b/urcu.c
@@ -42,6 +42,8 @@
#include "urcu-pointer.h"
#include "urcu/tls-compat.h"
+#include "urcu-die.h"
+
/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#undef _LGPL_SOURCE
#include "urcu.h"
@@ -110,17 +112,12 @@ static void mutex_lock(pthread_mutex_t *mutex)
#ifndef DISTRUST_SIGNALS_EXTREME
ret = pthread_mutex_lock(mutex);
- if (ret) {
- perror("Error in pthread mutex lock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
while ((ret = pthread_mutex_trylock(mutex)) != 0) {
- if (ret != EBUSY && ret != EINTR) {
- printf("ret = %d, errno = %d\n", ret, errno);
- perror("Error in pthread mutex lock");
- exit(-1);
- }
+ if (ret != EBUSY && ret != EINTR)
+ urcu_die(ret);
if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
cmm_smp_mb();
_CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
@@ -136,10 +133,8 @@ static void mutex_unlock(pthread_mutex_t *mutex)
int ret;
ret = pthread_mutex_unlock(mutex);
- if (ret) {
- perror("Error in pthread mutex unlock");
- exit(-1);
- }
+ if (ret)
+ urcu_die(ret);
}
#ifdef RCU_MEMBARRIER
@@ -432,10 +427,8 @@ void rcu_init(void)
act.sa_flags = SA_SIGINFO | SA_RESTART;
sigemptyset(&act.sa_mask);
ret = sigaction(SIGRCU, &act, NULL);
- if (ret) {
- perror("Error in sigaction");
- exit(-1);
- }
+ if (ret)
+ urcu_die(errno);
}
void rcu_exit(void)
@@ -444,10 +437,8 @@ void rcu_exit(void)
int ret;
ret = sigaction(SIGRCU, NULL, &act);
- if (ret) {
- perror("Error in sigaction");
- exit(-1);
- }
+ if (ret)
+ urcu_die(errno);
assert(act.sa_sigaction == sigrcu_handler);
assert(cds_list_empty(®istry));
}
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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