[PATCH RFC V4 1/6] perf tools: lock to protect namespaces and comm list

[kan . liang]

From: Kan Liang <kan.li...@intel.com>

Add two locks to protect namespaces_list and comm_list.

The lock is only needed for multithreaded code, so using mutex wrappers
provided by perf tool.

Not all the comm_list/namespaces_list accessing are protected, e.g.
thread__exec_comm. Because the multithread code for perf top event
synthesizing does not touch them. They don't need a lock.

Signed-off-by: Kan Liang <kan.li...@intel.com>
---
 tools/perf/util/thread.c | 53 +++++++++++++++++++++++++++++++++++++++++++-----
 tools/perf/util/thread.h |  3 +++
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index c09bdb5..bf73117 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -45,6 +45,8 @@ struct thread *thread__new(pid_t pid, pid_t tid)
                thread->cpu = -1;
                INIT_LIST_HEAD(&thread->namespaces_list);
                INIT_LIST_HEAD(&thread->comm_list);
+               init_rwsem(&thread->namespaces_lock);
+               init_rwsem(&thread->comm_lock);
 
                comm_str = malloc(32);
                if (!comm_str)
@@ -83,18 +85,26 @@ void thread__delete(struct thread *thread)
                map_groups__put(thread->mg);
                thread->mg = NULL;
        }
+       down_write(&thread->namespaces_lock);
        list_for_each_entry_safe(namespaces, tmp_namespaces,
                                 &thread->namespaces_list, list) {
                list_del(&namespaces->list);
                namespaces__free(namespaces);
        }
+       up_write(&thread->namespaces_lock);
+
+       down_write(&thread->comm_lock);
        list_for_each_entry_safe(comm, tmp_comm, &thread->comm_list, list) {
                list_del(&comm->list);
                comm__free(comm);
        }
+       up_write(&thread->comm_lock);
+
        unwind__finish_access(thread);
        nsinfo__zput(thread->nsinfo);
 
+       exit_rwsem(&thread->namespaces_lock);
+       exit_rwsem(&thread->comm_lock);
        free(thread);
 }
 
@@ -125,8 +135,8 @@ struct namespaces *thread__namespaces(const struct thread 
*thread)
        return list_first_entry(&thread->namespaces_list, struct namespaces, 
list);
 }
 
-int thread__set_namespaces(struct thread *thread, u64 timestamp,
-                          struct namespaces_event *event)
+static int __thread__set_namespaces(struct thread *thread, u64 timestamp,
+                                   struct namespaces_event *event)
 {
        struct namespaces *new, *curr = thread__namespaces(thread);
 
@@ -149,6 +159,17 @@ int thread__set_namespaces(struct thread *thread, u64 
timestamp,
        return 0;
 }
 
+int thread__set_namespaces(struct thread *thread, u64 timestamp,
+                          struct namespaces_event *event)
+{
+       int ret;
+
+       down_write(&thread->namespaces_lock);
+       ret = __thread__set_namespaces(thread, timestamp, event);
+       up_write(&thread->namespaces_lock);
+       return ret;
+}
+
 struct comm *thread__comm(const struct thread *thread)
 {
        if (list_empty(&thread->comm_list))
@@ -170,8 +191,8 @@ struct comm *thread__exec_comm(const struct thread *thread)
        return last;
 }
 
-int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
-                      bool exec)
+static int ____thread__set_comm(struct thread *thread, const char *str,
+                               u64 timestamp, bool exec)
 {
        struct comm *new, *curr = thread__comm(thread);
 
@@ -195,6 +216,17 @@ int __thread__set_comm(struct thread *thread, const char 
*str, u64 timestamp,
        return 0;
 }
 
+int __thread__set_comm(struct thread *thread, const char *str, u64 timestamp,
+                      bool exec)
+{
+       int ret;
+
+       down_write(&thread->comm_lock);
+       ret = ____thread__set_comm(thread, str, timestamp, exec);
+       up_write(&thread->comm_lock);
+       return ret;
+}
+
 int thread__set_comm_from_proc(struct thread *thread)
 {
        char path[64];
@@ -212,7 +244,7 @@ int thread__set_comm_from_proc(struct thread *thread)
        return err;
 }
 
-const char *thread__comm_str(const struct thread *thread)
+static const char *__thread__comm_str(const struct thread *thread)
 {
        const struct comm *comm = thread__comm(thread);
 
@@ -222,6 +254,17 @@ const char *thread__comm_str(const struct thread *thread)
        return comm__str(comm);
 }
 
+const char *thread__comm_str(const struct thread *thread)
+{
+       const char *str;
+
+       down_read((struct rw_semaphore *)&thread->comm_lock);
+       str = __thread__comm_str(thread);
+       up_read((struct rw_semaphore *)&thread->comm_lock);
+
+       return str;
+}
+
 /* CHECKME: it should probably better return the max comm len from its comm 
list */
 int thread__comm_len(struct thread *thread)
 {
diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h
index cb1a5dd..10555d6 100644
--- a/tools/perf/util/thread.h
+++ b/tools/perf/util/thread.h
@@ -9,6 +9,7 @@
 #include "symbol.h"
 #include <strlist.h>
 #include <intlist.h>
+#include "rwsem.h"
 
 struct thread_stack;
 struct unwind_libunwind_ops;
@@ -29,7 +30,9 @@ struct thread {
        int                     comm_len;
        bool                    dead; /* if set thread has exited */
        struct list_head        namespaces_list;
+       struct rw_semaphore     namespaces_lock;
        struct list_head        comm_list;
+       struct rw_semaphore     comm_lock;
        u64                     db_id;
 
        void                    *priv;
-- 
2.5.5