linux-kernel - [PATCH 2/2] creds: __task_cred(current) doesn't need rcu_read_lock

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Message-ID: <20110920143959.GC15859@redhat.com>
Date:	Tue, 20 Sep 2011 16:39:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	lkml <linux-kernel@...r.kernel.org>, richard@....at,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 2/2] creds: __task_cred(current) doesn't need
	rcu_read_lock_held()

Change __task_cred(task) to accept "task == current" without
rcu_read_lock_held(). This is what current_cred() currently does,
and with this change __task_cred() becomes more flexible/usable.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---

 include/linux/cred.h |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- 3.1/include/linux/cred.h~2_task_cred_ck_current	2011-09-20 16:28:47.000000000 +0200
+++ 3.1/include/linux/cred.h	2011-09-20 16:33:12.000000000 +0200
@@ -268,8 +268,7 @@ static inline void put_cred(const struct
  * Access the subjective credentials of the current task.  RCU-safe,
  * since nobody else can modify it.
  */
-#define current_cred() \
-	rcu_dereference_protected(current->cred, 1)
+#define current_cred()	__task_cred(current)
 
 /**
  * __task_cred - Access a task's objective credentials
@@ -284,7 +283,7 @@ static inline void put_cred(const struct
 #define __task_cred(task)						\
 	({								\
 		const struct task_struct *__t = (task);			\
-		rcu_dereference_check(__t->real_cred, 0);		\
+		rcu_dereference_check(__t->real_cred, (__t == current));\
 	})
 
 /**

--
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