From 8f92054e7ca1d3a3ae50fb42d2253ac8730d9b2a Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 29 Jul 2010 12:45:55 +0100 Subject: CRED: Fix __task_cred()'s lockdep check and banner comment Fix __task_cred()'s lockdep check by removing the following validation condition: lockdep_tasklist_lock_is_held() as commit_creds() does not take the tasklist_lock, and nor do most of the functions that call it, so this check is pointless and it can prevent detection of the RCU lock not being held if the tasklist_lock is held. Instead, add the following validation condition: task->exit_state >= 0 to permit the access if the target task is dead and therefore unable to change its own credentials. Fix __task_cred()'s comment to: (1) discard the bit that says that the caller must prevent the target task from being deleted. That shouldn't need saying. (2) Add a comment indicating the result of __task_cred() should not be passed directly to get_cred(), but rather than get_task_cred() should be used instead. Also put a note into the documentation to enforce this point there too. Signed-off-by: David Howells Acked-by: Jiri Olsa Cc: Paul E. McKenney Signed-off-by: Linus Torvalds --- include/linux/cred.h | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) (limited to 'include/linux/cred.h') diff --git a/include/linux/cred.h b/include/linux/cred.h index ce40cbc791e2..4d2c39573f36 100644 --- a/include/linux/cred.h +++ b/include/linux/cred.h @@ -274,13 +274,18 @@ static inline void put_cred(const struct cred *_cred) * @task: The task to query * * Access the objective credentials of a task. The caller must hold the RCU - * readlock. + * readlock or the task must be dead and unable to change its own credentials. * - * The caller must make sure task doesn't go away, either by holding a ref on - * task or by holding tasklist_lock to prevent it from being unlinked. + * The result of this function should not be passed directly to get_cred(); + * rather get_task_cred() should be used instead. */ -#define __task_cred(task) \ - ((const struct cred *)(rcu_dereference_check((task)->real_cred, rcu_read_lock_held() || lockdep_tasklist_lock_is_held()))) +#define __task_cred(task) \ + ({ \ + const struct task_struct *__t = (task); \ + rcu_dereference_check(__t->real_cred, \ + rcu_read_lock_held() || \ + task_is_dead(__t)); \ + }) /** * get_current_cred - Get the current task's subjective credentials -- cgit v1.2.1