lkml.org 
[lkml]   [2006]   [Aug]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] sys_getppid-oopses-on-debug-kernel-v2-simplify
On top of Kirill's sys_getppid-oopses-on-debug-kernel-v2.patch

- We don't need ->group_leader->real_parent, all threads should
have the same ->real_parent.

- We don't need tasklist_lock, task_struct is freed by RCU, so
rcu_read_lock() should be enough.

(Compile tested)

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- 2.6.18-rc3/kernel/timer.c~ 2006-08-09 22:08:51.000000000 +0400
+++ 2.6.18-rc3/kernel/timer.c 2006-08-09 22:15:35.000000000 +0400
@@ -1324,28 +1324,18 @@ asmlinkage long sys_getpid(void)
}

/*
- * Accessing ->group_leader->real_parent is not SMP-safe, it could
- * change from under us. However, rather than getting any lock
- * we can use an optimistic algorithm: get the parent
- * pid, and go back and check that the parent is still
- * the same. If it has changed (which is extremely unlikely
- * indeed), we just try again..
- *
- * NOTE! This depends on the fact that even if we _do_
- * get an old value of "parent", we can happily dereference
- * the pointer (it was and remains a dereferencable kernel pointer
- * no matter what): we just can't necessarily trust the result
- * until we know that the parent pointer is valid.
- *
- * NOTE2: ->group_leader never changes from under us.
+ * Accessing ->real_parent is not SMP-safe, it could
+ * change from under us. However, we can use a stale
+ * value of ->real_parent under rcu_read_lock(), see
+ * release_task()->call_rcu(delayed_put_task_struct).
*/
asmlinkage long sys_getppid(void)
{
int pid;

- read_lock(&tasklist_lock);
- pid = current->group_leader->real_parent->tgid;
- read_unlock(&tasklist_lock);
+ rcu_read_lock();
+ pid = rcu_dereference(current->real_parent)->tgid;
+ rcu_read_unlock();

return pid;
}
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-08-09 16:03    [W:0.398 / U:0.148 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site