The patch titled
sys_getppid-oopses-on-debug-kernel-v2-simplify
has been added to the -mm tree. Its filename is
sys_getppid-oopses-on-debug-kernel-v2-simplify.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: sys_getppid-oopses-on-debug-kernel-v2-simplify
From: Oleg Nesterov <oleg@xxxxxxxxxx>
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.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Kirill Korotaev <dev@xxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/timer.c | 24 +++++++-----------------
1 files changed, 7 insertions(+), 17 deletions(-)
diff -puN kernel/timer.c~sys_getppid-oopses-on-debug-kernel-v2-simplify kernel/timer.c
--- a/kernel/timer.c~sys_getppid-oopses-on-debug-kernel-v2-simplify
+++ a/kernel/timer.c
@@ -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;
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
sys_getppid-oopses-on-debug-kernel-v2-simplify.patch
pid-implement-transfer_pid-and-use-it-to-simplify-de_thread.patch
pid-remove-temporary-debug-code-in-attach_pid.patch
rtmutex-clean-up-and-remove-some-extra-spinlocks.patch
pidhash-temporary-debug-checks.patch
-
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