This patch adds lock_task_sighand() helper and converts
group_send_sig_info() to use it. Hopefully we will have
more users soon.
This patch also removes '!sighand->count' and '!p->usage'
checks, I think they both are bogus, racy and unneeded
(but probably it makes sense to restore them as BUG_ON()s).
->sighand is cleared and it's ->count is decremented in
release_task() with sighand->siglock held, so it is a bug
to have '!p->usage || !->count' after we already locked and
verified it is the same. On the other hand, an already dead
task without ->sighand can have a non-zero ->usage due to
ptrace, for example.
If we read the stale value of ->sighand we must see the change
after spin_lock(), because that change was done while holding
that same old ->sighand.siglock.
Signed-off-by: Oleg Nesterov <[email protected]>
--- 2.6.16-rc3/include/linux/sched.h~2_LTS 2006-02-18 00:05:20.000000000 +0300
+++ 2.6.16-rc3/include/linux/sched.h 2006-02-18 22:13:44.000000000 +0300
@@ -1217,6 +1217,15 @@ static inline void task_unlock(struct ta
spin_unlock(&p->alloc_lock);
}
+extern struct sighand_struct *lock_task_sighand(struct task_struct *tsk,
+ unsigned long *flags);
+
+static inline void unlock_task_sighand(struct task_struct *tsk,
+ unsigned long *flags)
+{
+ spin_unlock_irqrestore(&tsk->sighand->siglock, *flags);
+}
+
#ifndef __HAVE_THREAD_FUNCTIONS
#define task_thread_info(task) (task)->thread_info
--- 2.6.16-rc3/kernel/signal.c~2_LTS 2006-02-18 00:07:37.000000000 +0300
+++ 2.6.16-rc3/kernel/signal.c 2006-02-18 22:34:22.000000000 +0300
@@ -1120,31 +1120,41 @@ void zap_other_threads(struct task_struc
/*
* Must be called under rcu_read_lock() or with tasklist_lock read-held.
*/
-int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
-{
- unsigned long flags;
- struct sighand_struct *sp;
- int ret;
-
-retry:
- ret = check_kill_permission(sig, info, p);
- if (!ret && sig && (sp = rcu_dereference(p->sighand))) {
- spin_lock_irqsave(&sp->siglock, flags);
- if (p->sighand != sp) {
- spin_unlock_irqrestore(&sp->siglock, flags);
- goto retry;
- }
- if ((atomic_read(&sp->count) == 0) ||
- (atomic_read(&p->usage) == 0)) {
- spin_unlock_irqrestore(&sp->siglock, flags);
- return -ESRCH;
- }
- ret = __group_send_sig_info(sig, info, p);
- spin_unlock_irqrestore(&sp->siglock, flags);
- }
-
- return ret;
-}
+struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long *flags)
+{
+ struct sighand_struct *sighand;
+
+ for (;;) {
+ sighand = rcu_dereference(tsk->sighand);
+ if (unlikely(sighand == NULL))
+ break;
+
+ spin_lock_irqsave(&sighand->siglock, *flags);
+ if (likely(sighand == tsk->sighand))
+ break;
+ spin_unlock_irqrestore(&sighand->siglock, *flags);
+ }
+
+ return sighand;
+}
+
+int group_send_sig_info(int sig, struct siginfo *info, struct task_struct *p)
+{
+ unsigned long flags;
+ int ret;
+
+ ret = check_kill_permission(sig, info, p);
+
+ if (!ret && sig) {
+ ret = -ESRCH;
+ if (lock_task_sighand(p, &flags)) {
+ ret = __group_send_sig_info(sig, info, p);
+ unlock_task_sighand(p, &flags);
+ }
+ }
+
+ return ret;
+}
/*
* kill_pg_info() sends a signal to a process group: this is what the tty
-
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