[tip:core/urgent] signals: Fix more rcu assumptions

tip-bot for Thomas Gleixner
2009-12-10T22:10:06Z

Commit-ID: 7cf7db8df0b78076eafa4ead47559344ca7b7a43
Gitweb: http://git.kernel.org/tip/7cf7db8df0b78076eafa4ead47559344ca7b7a43
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Thu, 10 Dec 2009 00:53:21 +0000
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 10 Dec 2009 23:04:11 +0100

signals: Fix more rcu assumptions

1) Remove the misleading comment in __sigqueue_alloc() which claims
that holding a spinlock is equivalent to rcu_read_lock().

2) Add a rcu_read_lock/unlock around the __task_cred() access
in __sigqueue_alloc()

This needs to be revisited to remove the remaining users of
read_lock(&tasklist_lock) but that's outside the scope of this patch.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091210004703.269843657@linutronix.de>
---
kernel/signal.c | 8 ++++----
1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 7331656..f67545f 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -218,13 +218,13 @@ __sigqueue_alloc(int sig, struct task_struct *t, gfp_t flags, int override_rlimi
struct user_struct *user;

/*
- * We won't get problems with the target's UID changing under us
- * because changing it requires RCU be used, and if t != current, the
- * caller must be holding the RCU readlock (by way of a spinlock) and
- * we use RCU protection here
+ * Protect access to @t credentials. This can go away when all
+ * callers hold rcu read lock.
*/
+ rcu_read_lock();
user = get_uid(__task_cred(t)->user);
atomic_inc(&user->sigpending);
+ rcu_read_unlock();

if (override_rlimit ||
atomic_read(&user->sigpending) <=