Merge "Use sequence number to check if to reload atrace tags."

am: 445234c76c

Change-Id: Idccf520a3b3c06923f99a9a342111212fedaf358

libcutils/include/cutils/trace.h

@@ -25,7 +25,6 @@
 #include <sys/cdefs.h>
 #include <sys/types.h>
 #include <unistd.h>
-
 #include <cutils/compiler.h>
 
 __BEGIN_DECLS
@@ -89,6 +88,12 @@ __BEGIN_DECLS
 #error ATRACE_TAG must be defined to be one of the tags defined in cutils/trace.h
 #endif
 
+// Set this to 0 to revert to the old Binder-based atrace implementation.
+// This is only here in case rollbacks do not apply cleanly.
+// TODO(fmayer): Remove this once we are confident this won't need to be
+// rolled back, no later than 2020-03-01.
+#define ATRACE_SHMEM 1
+
 /**
  * Opens the trace file for writing and reads the property for initial tags.
  * The atrace.tags.enableflags property sets the tags to trace.
@@ -116,11 +121,15 @@ void atrace_set_debuggable(bool debuggable);
  * prevent tracing within the Zygote process.
  */
 void atrace_set_tracing_enabled(bool enabled);
-
 /**
- * Flag indicating whether setup has been completed, initialized to 0.
- * Nonzero indicates setup has completed.
- * Note: This does NOT indicate whether or not setup was successful.
+ * If !ATRACE_SHMEM:
+ *   Flag indicating whether setup has been completed, initialized to 0.
+ *   Nonzero indicates setup has completed.
+ *   Note: This does NOT indicate whether or not setup was successful.
+ * If ATRACE_SHMEM:
+ *   This is always set to false. This forces code that uses an old version
+ *   of this header to always call into atrace_setup, in which we call
+ *   atrace_init unconditionally.
  */
 extern atomic_bool atrace_is_ready;
 
@@ -143,6 +152,12 @@ extern int atrace_marker_fd;
  * This can be explicitly run to avoid setup delay on first trace function.
  */
 #define ATRACE_INIT() atrace_init()
+#define ATRACE_GET_ENABLED_TAGS() atrace_get_enabled_tags()
+
+#if ATRACE_SHMEM
+void atrace_init();
+uint64_t atrace_get_enabled_tags();
+#else
 static inline void atrace_init()
 {
     if (CC_UNLIKELY(!atomic_load_explicit(&atrace_is_ready, memory_order_acquire))) {
@@ -155,12 +170,12 @@ static inline void atrace_init()
  * It can be used as a guard condition around more expensive trace calculations.
  * Every trace function calls this, which ensures atrace_init is run.
  */
-#define ATRACE_GET_ENABLED_TAGS() atrace_get_enabled_tags()
 static inline uint64_t atrace_get_enabled_tags()
 {
     atrace_init();
     return atrace_enabled_tags;
 }
+#endif
 
 /**
  * Test if a given tag is currently enabled.

libcutils/trace-container.cpp

@@ -39,6 +39,11 @@ static int              atrace_container_sock_fd     = -1;
 static pthread_mutex_t  atrace_enabling_mutex        = PTHREAD_MUTEX_INITIALIZER;
 static pthread_rwlock_t atrace_container_sock_rwlock = PTHREAD_RWLOCK_INITIALIZER;
 
+static void atrace_seq_number_changed(uint32_t, uint32_t seq_no) {
+    pthread_once(&atrace_once_control, atrace_init_once);
+    atomic_store_explicit(&last_sequence_number, seq_no, memory_order_relaxed);
+}
+
 static bool atrace_init_container_sock()
 {
     pthread_rwlock_wrlock(&atrace_container_sock_rwlock);

libcutils/trace-dev.cpp

@@ -37,12 +37,39 @@ static void atrace_init_once()
     } else {
       atrace_enabled_tags = atrace_get_property();
     }
+#if !ATRACE_SHMEM
     atomic_store_explicit(&atrace_is_ready, true, memory_order_release);
+#endif
+}
+
+static void atrace_seq_number_changed(uint32_t prev_seq_no, uint32_t seq_no) {
+    if (!atomic_load_explicit(&atrace_is_enabled, memory_order_acquire)) {
+        return;
+    }
+
+    // Someone raced us.
+    if (!atomic_compare_exchange_strong(&last_sequence_number, &prev_seq_no, seq_no)) {
+        return;
+    }
+
+    if (CC_UNLIKELY(prev_seq_no == kSeqNoNotInit)) {
+#if defined(__BIONIC__)
+        const prop_info* new_pi = __system_property_find("debug.atrace.tags.enableflags");
+        if (new_pi) atrace_property_info = new_pi;
+#endif
+        pthread_once(&atrace_once_control, atrace_init_once);
+    }
+
+    atrace_update_tags();
 }
 
 void atrace_setup()
 {
+#if ATRACE_SHMEM
+    atrace_init();
+#else
     pthread_once(&atrace_once_control, atrace_init_once);
+#endif
 }
 
 void atrace_begin_body(const char* name)

libcutils/trace-dev.inc

@@ -34,6 +34,11 @@
 #include <log/log.h>
 #include <log/log_properties.h>
 
+#if defined(__BIONIC__)
+#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
+#include <sys/_system_properties.h>
+#endif
+
 /**
  * Maximum size of a message that can be logged to the trace buffer.
  * Note this message includes a tag, the pid, and the string given as the name.
@@ -41,12 +46,57 @@
  */
 #define ATRACE_MESSAGE_LENGTH 1024
 
-atomic_bool             atrace_is_ready      = ATOMIC_VAR_INIT(false);
-int                     atrace_marker_fd     = -1;
-uint64_t                atrace_enabled_tags  = ATRACE_TAG_NOT_READY;
-static bool             atrace_is_debuggable = false;
-static atomic_bool      atrace_is_enabled    = ATOMIC_VAR_INIT(true);
-static pthread_mutex_t  atrace_tags_mutex    = PTHREAD_MUTEX_INITIALIZER;
+constexpr uint32_t kSeqNoNotInit = static_cast<uint32_t>(-1);
+
+atomic_bool              atrace_is_ready      = ATOMIC_VAR_INIT(false);
+int                      atrace_marker_fd     = -1;
+uint64_t                 atrace_enabled_tags  = ATRACE_TAG_NOT_READY;
+static bool              atrace_is_debuggable = false;
+static atomic_bool       atrace_is_enabled    = ATOMIC_VAR_INIT(true);
+static pthread_mutex_t   atrace_tags_mutex    = PTHREAD_MUTEX_INITIALIZER;
+
+/**
+ * Sequence number of debug.atrace.tags.enableflags the last time the enabled
+ * tags were reloaded.
+ **/
+static _Atomic(uint32_t) last_sequence_number = ATOMIC_VAR_INIT(kSeqNoNotInit);
+
+#if defined(__BIONIC__)
+// All zero prop_info that has a sequence number of 0. This is easier than
+// depending on implementation details of the property implementation.
+//
+// prop_info is static_assert-ed to be 96 bytes, which cannot change due to
+// ABI compatibility.
+alignas(uint64_t) static char empty_pi[96];
+static const prop_info* atrace_property_info = reinterpret_cast<const prop_info*>(empty_pi);
+#endif
+
+#if ATRACE_SHMEM
+
+/**
+ * This is called when the sequence number of debug.atrace.tags.enableflags
+ * changes and we need to reload the enabled tags.
+ **/
+static void atrace_seq_number_changed(uint32_t prev_seq_no, uint32_t seq_no);
+
+void atrace_init() {
+#if defined(__BIONIC__)
+    uint32_t seq_no = __system_property_serial(atrace_property_info);  // Acquire semantics.
+#else
+    uint32_t seq_no = 0;
+#endif
+    uint32_t prev_seq_no = atomic_load_explicit(&last_sequence_number, memory_order_relaxed);
+    if (CC_UNLIKELY(seq_no != prev_seq_no)) {
+        atrace_seq_number_changed(prev_seq_no, seq_no);
+    }
+}
+
+uint64_t atrace_get_enabled_tags()
+{
+    atrace_init();
+    return atrace_enabled_tags;
+}
+#endif
 
 // Set whether this process is debuggable, which determines whether
 // application-level tracing is allowed when the ro.debuggable system property
@@ -136,7 +186,7 @@ static uint64_t atrace_get_property()
 void atrace_update_tags()
 {
     uint64_t tags;
-    if (CC_UNLIKELY(atomic_load_explicit(&atrace_is_ready, memory_order_acquire))) {
+    if (ATRACE_SHMEM || CC_UNLIKELY(atomic_load_explicit(&atrace_is_ready, memory_order_acquire))) {
         if (atomic_load_explicit(&atrace_is_enabled, memory_order_acquire)) {
             tags = atrace_get_property();
             pthread_mutex_lock(&atrace_tags_mutex);

libcutils/trace-host.cpp

@@ -30,3 +30,10 @@ void atrace_async_begin_body(const char* /*name*/, int32_t /*cookie*/) {}
 void atrace_async_end_body(const char* /*name*/, int32_t /*cookie*/) {}
 void atrace_int_body(const char* /*name*/, int32_t /*value*/) {}
 void atrace_int64_body(const char* /*name*/, int64_t /*value*/) {}
+#if ATRACE_SHMEM
+void atrace_init() {}
+uint64_t atrace_get_enabled_tags()
+{
+    return ATRACE_TAG_NOT_READY;
+}
+#endif