[lxc-devel] [PATCH] check pthread_atfork and thread-local storage support
S.Çağlar Onur
caglar at 10ur.org
Sat Jan 4 05:00:04 UTC 2014
This patch;
Adds pthread_atfork check to configure.ac and uses it when necessary,
Introduces tls.m4 macro for checking thread-local storage support,
Puts values array into thread-local storage (lxc_global_config_value at src/lxc/utils.c),
Removes static_lock/static_unlock from LXC code,
Lastly, it introduces a warning for bionic users about multithreaded usage of LXC.
(requires 64b1be2903078ef9e9ba3ffcbc30a4dc9bc5cc6c to be reverted first)
Signed-off-by: S.Çağlar Onur <caglar at 10ur.org>
---
config/tls.m4 | 14 ++++++++++++++
configure.ac | 15 +++++++++++++++
src/lxc/lxclock.c | 21 ++-------------------
src/lxc/lxclock.h | 10 ----------
src/lxc/utils.c | 23 +++++++----------------
5 files changed, 38 insertions(+), 45 deletions(-)
create mode 100644 config/tls.m4
diff --git a/config/tls.m4 b/config/tls.m4
new file mode 100644
index 0000000..5d1ac59
--- /dev/null
+++ b/config/tls.m4
@@ -0,0 +1,14 @@
+# See if we have working TLS. We only check to see if it compiles, and that
+# the resulting program actually runs, not whether the resulting TLS variables
+# work properly; that check is done at runtime, since we can run binaries
+# compiled with __thread on systems without TLS.
+AC_DEFUN([LXC_CHECK_TLS],
+[
+ AC_MSG_CHECKING(for TLS)
+ AC_RUN_IFELSE([AC_LANG_SOURCE([[ static __thread int val; int main() { return 0; } ]])],[have_tls=yes],[have_tls=no],[have_tls=no ])
+ AC_MSG_RESULT($have_tls)
+ if test "$have_tls" = "yes"; then
+ AC_DEFINE([HAVE_TLS],[1],[Define if the compiler supports __thread])
+ AC_DEFINE([thread_local],[__thread],[Define to the compiler TLS keyword])
+ fi
+])
diff --git a/configure.ac b/configure.ac
index 2d24937..af0991d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -483,6 +483,8 @@ AC_CHECK_HEADERS([sys/signalfd.h pty.h ifaddrs.h sys/capability.h sys/personalit
AC_CHECK_FUNCS([setns pivot_root sethostname unshare rand_r confstr])
# Check for some functions
+AC_CHECK_LIB(pthread, main)
+AC_CHECK_FUNCS(pthread_atfork)
AC_CHECK_LIB(util, openpty)
AC_CHECK_FUNCS([openpty hasmntopt setmntent endmntent])
AC_CHECK_FUNCS([getline],
@@ -502,6 +504,9 @@ AC_SEARCH_LIBS(clock_gettime, [rt])
AC_PROG_GCC_TRADITIONAL
AC_PROG_SED
+# See if we support thread-local storage.
+LXC_CHECK_TLS
+
if test "x$GCC" = "xyes"; then
CFLAGS="$CFLAGS -Wall -Werror"
fi
@@ -680,3 +685,13 @@ Debugging:
Paths:
- Logs in configpath: $enable_configpath_log
EOF
+
+if test "x$ac_cv_func_pthread_atfork" = "xno" ; then
+cat << EOF
+
+WARNING: Threading not supported on your platform
+
+ You are compiling LXC for bionic target which lacks certain threading related functionality used by LXC API (like pthread_atfork).
+ Please note that, because of the missing functionality, multithreaded usage of LXC API cause some problems.
+EOF
+fi
diff --git a/src/lxc/lxclock.c b/src/lxc/lxclock.c
index b0420bb..3e1b054 100644
--- a/src/lxc/lxclock.c
+++ b/src/lxc/lxclock.c
@@ -46,7 +46,6 @@ lxc_log_define(lxc_lock, lxc);
#ifdef MUTEX_DEBUGGING
static pthread_mutex_t thread_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
-static pthread_mutex_t static_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
static inline void dump_stacktrace(void)
{
@@ -68,7 +67,6 @@ static inline void dump_stacktrace(void)
}
#else
static pthread_mutex_t thread_mutex = PTHREAD_MUTEX_INITIALIZER;
-static pthread_mutex_t static_mutex = PTHREAD_MUTEX_INITIALIZER;
static inline void dump_stacktrace(void) {;}
#endif
@@ -326,28 +324,13 @@ void process_unlock(void)
* to unlock the mutex.
* This forbids doing fork() while explicitly holding the lock.
*/
+#ifdef HAVE_PTHREAD_ATFORK
__attribute__((constructor))
static void process_lock_setup_atfork(void)
{
pthread_atfork(process_lock, process_unlock, process_unlock);
}
-
-/* Protects static const values inside the lxc_global_config_value funtion */
-void static_lock(void)
-{
- lock_mutex(&static_mutex);
-}
-
-void static_unlock(void)
-{
- unlock_mutex(&static_mutex);
-}
-
-__attribute__((constructor))
-static void static_lock_setup_atfork(void)
-{
- pthread_atfork(static_lock, static_unlock, static_unlock);
-}
+#endif
int container_mem_lock(struct lxc_container *c)
{
diff --git a/src/lxc/lxclock.h b/src/lxc/lxclock.h
index 820e819..a02a032 100644
--- a/src/lxc/lxclock.h
+++ b/src/lxc/lxclock.h
@@ -123,16 +123,6 @@ extern void process_lock(void);
*/
extern void process_unlock(void);
-/*!
- * \brief Lock global data.
- */
-extern void static_lock(void);
-
-/*!
- * \brief Unlock global data.
- */
-extern void static_unlock(void);
-
struct lxc_container;
/*!
diff --git a/src/lxc/utils.c b/src/lxc/utils.c
index 1f9ceea..5f2c8b2 100644
--- a/src/lxc/utils.c
+++ b/src/lxc/utils.c
@@ -250,9 +250,12 @@ static const char *lxc_global_config_value(const char *option_name)
{ NULL, NULL },
};
- /* Protected by a mutex to eliminate conflicting load and store operations */
+ /* placed in the thread local storage pool for non-bionic targets */
+#ifdef HAVE_TLS
+ static __thread const char *values[sizeof(options) / sizeof(options[0])] = { 0 };
+#else
static const char *values[sizeof(options) / sizeof(options[0])] = { 0 };
-
+#endif
char *user_config_path = NULL;
char *user_lxc_path = NULL;
@@ -273,7 +276,6 @@ static const char *lxc_global_config_value(const char *option_name)
}
const char * const (*ptr)[2];
- const char *value;
size_t i;
char buf[1024], *p, *p2;
FILE *fin = NULL;
@@ -289,15 +291,11 @@ static const char *lxc_global_config_value(const char *option_name)
return NULL;
}
- static_lock();
if (values[i]) {
free(user_config_path);
free(user_lxc_path);
- value = values[i];
- static_unlock();
- return value;
+ return values[i];
}
- static_unlock();
fin = fopen_cloexec(user_config_path, "r");
free(user_config_path);
@@ -333,15 +331,12 @@ static const char *lxc_global_config_value(const char *option_name)
while (*p && (*p == ' ' || *p == '\t')) p++;
if (!*p)
continue;
- static_lock();
values[i] = copy_global_config_value(p);
- static_unlock();
free(user_lxc_path);
goto out;
}
}
/* could not find value, use default */
- static_lock();
if (strcmp(option_name, "lxcpath") == 0)
values[i] = user_lxc_path;
else {
@@ -353,16 +348,12 @@ static const char *lxc_global_config_value(const char *option_name)
* as an error... */
if (!values[i])
errno = 0;
- static_unlock();
out:
if (fin)
fclose(fin);
- static_lock();
- value = values[i];
- static_unlock();
- return value;
+ return values[i];
}
const char *default_lvm_vg(void)
--
1.8.3.2
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