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[PATCH] Keys: Improve usage of memory barriers and remove IRQ disablement

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Remove an unnecessary memory barrier (implicit in rcu_dereference()) from
install_session_keyring().

install_session_keyring() is also rearranged a little to make it slightly
more efficient.

As install_*_keyring() may schedule (in synchronize_rcu() or
keyring_alloc()), they may not be entered with interrupts disabled - and so
there's no point saving the interrupt disablement state over the critical
section.

exec_keys() will also be invoked with interrupts enabled, and so that doesn't
need to save the interrupt state either.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
David Howells 2006-04-10 22:54:26 -07:00 committed by Linus Torvalds
parent 25a80759c5
commit 1a26feb962
1 changed files with 20 additions and 21 deletions
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41
security/keys/process_keys.c
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@ -168,11 +168,12 @@ int install_thread_keyring(struct task_struct *tsk)
*/
int install_process_keyring(struct task_struct *tsk)
{
unsigned long flags;
struct key *keyring;
char buf[20];
int ret;
might_sleep();
if (!tsk->signal->process_keyring) {
sprintf(buf, "_pid.%u", tsk->tgid);
@ -183,12 +184,12 @@ int install_process_keyring(struct task_struct *tsk)
}
/* attach keyring */
spin_lock_irqsave(&tsk->sighand->siglock, flags);
spin_lock_irq(&tsk->sighand->siglock);
if (!tsk->signal->process_keyring) {
tsk->signal->process_keyring = keyring;
keyring = NULL;
}
spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
spin_unlock_irq(&tsk->sighand->siglock);
key_put(keyring);
}
@ -207,38 +208,37 @@ int install_process_keyring(struct task_struct *tsk)
static int install_session_keyring(struct task_struct *tsk,
struct key *keyring)
{
unsigned long flags;
struct key *old;
char buf[20];
int ret;
might_sleep();
/* create an empty session keyring */
if (!keyring) {
sprintf(buf, "_ses.%u", tsk->tgid);
keyring = keyring_alloc(buf, tsk->uid, tsk->gid, 1, NULL);
if (IS_ERR(keyring)) {
ret = PTR_ERR(keyring);
goto error;
}
if (IS_ERR(keyring))
return PTR_ERR(keyring);
}
else {
atomic_inc(&keyring->usage);
}
/* install the keyring */
spin_lock_irqsave(&tsk->sighand->siglock, flags);
old = rcu_dereference(tsk->signal->session_keyring);
spin_lock_irq(&tsk->sighand->siglock);
old = tsk->signal->session_keyring;
rcu_assign_pointer(tsk->signal->session_keyring, keyring);
spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
spin_unlock_irq(&tsk->sighand->siglock);
ret = 0;
/* we're using RCU on the pointer, but there's no point synchronising
* on it if it didn't previously point to anything */
if (old) {
synchronize_rcu();
key_put(old);
}
/* we're using RCU on the pointer */
synchronize_rcu();
key_put(old);
error:
return ret;
return 0;
} /* end install_session_keyring() */
@ -311,7 +311,6 @@ void exit_keys(struct task_struct *tsk)
*/
int exec_keys(struct task_struct *tsk)
{
unsigned long flags;
struct key *old;
/* newly exec'd tasks don't get a thread keyring */
@ -323,10 +322,10 @@ int exec_keys(struct task_struct *tsk)
key_put(old);
/* discard the process keyring from a newly exec'd task */
spin_lock_irqsave(&tsk->sighand->siglock, flags);
spin_lock_irq(&tsk->sighand->siglock);
old = tsk->signal->process_keyring;
tsk->signal->process_keyring = NULL;
spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
spin_unlock_irq(&tsk->sighand->siglock);
key_put(old);