Move the comment from utrace_task_alloc() to utrace_add_engine()
and try to make it a bit more clear.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
include/linux/utrace.h | 4 ++--
kernel/utrace.c | 11 +++++------
2 files changed, 7 insertions(+), 8 deletions(-)
--- UTRACE-PTRACE/include/linux/utrace.h~4_ADD_ENGINE_DOCUMENT_IMPLICIT_MB
2009-11-21 15:12:27.000000000 +0100
+++ UTRACE-PTRACE/include/linux/utrace.h 2009-12-12 17:42:16.000000000
+0100
@@ -164,8 +164,8 @@ static inline struct utrace *task_utrace
* is ordered before this load of task->utrace. We use those
* utrace_flags checks in the hot path to decide to call into
* the utrace code. The first attach installs task->utrace before
- * setting task->utrace_flags nonzero, with a barrier between.
- * See utrace_task_alloc().
+ * setting task->utrace_flags nonzero with implicit barrier in
+ * between, see utrace_add_engine().
*/
smp_rmb();
utrace = task->utrace;
--- UTRACE-PTRACE/kernel/utrace.c~4_ADD_ENGINE_DOCUMENT_IMPLICIT_MB
2009-12-12 16:49:26.000000000 +0100
+++ UTRACE-PTRACE/kernel/utrace.c 2009-12-12 17:46:55.000000000 +0100
@@ -107,11 +107,7 @@ static bool utrace_task_alloc(struct tas
task->utrace = utrace;
}
task_unlock(task);
- /*
- * That unlock after storing task->utrace acts as a memory barrier
- * ordering any subsequent task->utrace_flags store afterwards.
- * This pairs with smp_rmb() in task_utrace_struct().
- */
+
if (unlikely(task->utrace != utrace))
kmem_cache_free(utrace_cachep, utrace);
return true;
@@ -221,7 +217,10 @@ static int utrace_add_engine(struct task
/*
* In case we had no engines before, make sure that
- * utrace_flags is not zero.
+ * utrace_flags is not zero. Since we did unlock+lock
+ * at least once after utrace_task_alloc() installed
+ * ->utrace, we have the necessary barrier which pairs
+ * with rmb() in task_utrace_struct().
*/
ret = -ESRCH;
if (!target->utrace_flags) {
