tracehook: wait_task_inactive

This extends wait_task_inactive() with a new argument so it can be used in
a "soft" mode where it will check for the task changing state unexpectedly
and back off.  There is no change to existing callers.  This lays the
groundwork to allow robust, noninvasive tracing that can try to sample a
blocked thread but back off safely if it wakes up.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a95d84d0da95..f59318a0099b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1882,9 +1882,13 @@ extern void set_task_comm(struct task_struct *tsk, char *from);
 extern char *get_task_comm(char *to, struct task_struct *tsk);
 
 #ifdef CONFIG_SMP
-extern void wait_task_inactive(struct task_struct * p);
+extern unsigned long wait_task_inactive(struct task_struct *, long match_state);
 #else
-#define wait_task_inactive(p)   do { } while (0)
+static inline unsigned long wait_task_inactive(struct task_struct *p,
+                                               long match_state)
+{
+        return 1;
+}
 #endif
 
 #define next_task(p)    list_entry(rcu_dereference((p)->tasks.next), struct task_struct, tasks)