logging: make nm-logging thread-safe

NetworkManager is single-threaded and uses a mainloop.

However, sometimes we may need multiple threads. For example, we will
need to write sysctl values asynchronously, using the glib thread-pool.
For that to work, we also need to switch the network-namespace of the
thread-pool thread. We want to use NMPNetns for that. Hence it's better
to have NMPNetns thread-safe, instead of coming up with a duplicate
implementation. But NMPNetns may want to log, so we also need nm-logging
thread-safe.

In general, code under "shared/nm-utils" and nm-logging should be usable
from multiple threads. It's simpler to make this code thread-safe than
re-implementing it. Also, it's a bad limitation to be unable to log
from other threads. If there is an error, the best we can often do is to
log about it.

Make nm-logging thread-safe. Actually, we only need to be able to log
from multiple threads. We don't need to setup or configure logging from
multiple threads. This restriction allows us to access logging from the
main-thread without any thread-synchronization (because all changes in
the logging setup are also done from the main-thread).

So, while logging from other threads requires a mutex, logging from the
main-thread is lock-free.

1 files changed, 28 insertions, 3 deletions

diff --git a/src/nm-logging.h b/src/nm-logging.h
index e7b307c23e..a824890a1c 100644
--- a/src/nm-logging.h
+++ b/src/nm-logging.h
@@ -54,10 +54,12 @@ LOGD_IP_from_af (int addr_family)
 /* A wrapper for the _nm_log_impl() function that adds call site information.
  * Contrary to nm_log(), it unconditionally calls the function without
  * checking whether logging for the given level and domain is enabled. */
-#define _nm_log(level, domain, error, ifname, con_uuid, ...) \
+#define _nm_log_mt(mt_require_locking, level, domain, error, ifname, con_uuid, ...) \
     G_STMT_START { \
-        _nm_log_impl (__FILE__, __LINE__, \
+        _nm_log_impl (__FILE__, \
+                      __LINE__, \
                       _NM_LOG_FUNC, \
+                      (mt_require_locking), \
                       (level), \
                       (domain), \
                       (error), \
@@ -66,6 +68,9 @@ LOGD_IP_from_af (int addr_family)
                       ""__VA_ARGS__); \
     } G_STMT_END
 
+#define _nm_log(level, domain, error, ifname, con_uuid, ...) \
+	_nm_log_mt (!(NM_THREAD_SAFE_ON_MAIN_THREAD), level, domain, error, ifname, con_uuid, __VA_ARGS__)
+
 /* nm_log() only evaluates its argument list after checking
  * whether logging for the given level/domain is enabled.  */
 #define nm_log(level, domain, ifname, con_uuid, ...) \
@@ -138,15 +143,35 @@ _nm_log_ptr_is_debug (NMLogLevel level)
 const char *nm_logging_level_to_string (void);
 const char *nm_logging_domains_to_string (void);
 
+/*****************************************************************************/
+
 extern NMLogDomain _nm_logging_enabled_state[_LOGL_N_REAL];
+
 static inline gboolean
-nm_logging_enabled (NMLogLevel level, NMLogDomain domain)
+_nm_logging_enabled_lockfree (NMLogLevel level, NMLogDomain domain)
 {
 	nm_assert (((guint) level) < G_N_ELEMENTS (_nm_logging_enabled_state));
 	return    (((guint) level) < G_N_ELEMENTS (_nm_logging_enabled_state))
 	       && !!(_nm_logging_enabled_state[level] & domain);
 }
 
+gboolean _nm_logging_enabled_locking (NMLogLevel level, NMLogDomain domain);
+
+static inline gboolean
+nm_logging_enabled_mt (gboolean mt_require_locking, NMLogLevel level, NMLogDomain domain)
+{
+	if (mt_require_locking)
+		return _nm_logging_enabled_locking (level, domain);
+
+	NM_ASSERT_ON_MAIN_THREAD ();
+	return _nm_logging_enabled_lockfree (level, domain);
+}
+
+#define nm_logging_enabled(level, domain) \
+	nm_logging_enabled_mt (!(NM_THREAD_SAFE_ON_MAIN_THREAD), level, domain)
+
+/*****************************************************************************/
+
 NMLogLevel nm_logging_get_level (NMLogDomain domain);
 
 const char *nm_logging_all_levels_to_string (void);