[PATCH] introduce lock_task_sighand() helper
Add 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 <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index bbcfc87..ca1fd31 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1225,6 +1225,15 @@
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