signals: do_tkill: don't use tasklist_lock
Convert do_tkill() to use rcu_read_lock() + lock_task_sighand() to avoid
taking tasklist lock.
Note that we don't return an error if lock_task_sighand() fails, we pretend
the task dies after receiving the signal. Otherwise, we should fight with the
nasty races with mt-exec without having any advantage.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/signal.c b/kernel/signal.c
index b3dedf1..13371d1 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2219,6 +2219,7 @@
int error;
struct siginfo info;
struct task_struct *p;
+ unsigned long flags;
error = -ESRCH;
info.si_signo = sig;
@@ -2227,21 +2228,24 @@
info.si_pid = task_tgid_vnr(current);
info.si_uid = current->uid;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
p = find_task_by_vpid(pid);
if (p && (tgid <= 0 || task_tgid_vnr(p) == tgid)) {
error = check_kill_permission(sig, &info, p);
/*
* The null signal is a permissions and process existence
* probe. No signal is actually delivered.
+ *
+ * If lock_task_sighand() fails we pretend the task dies
+ * after receiving the signal. The window is tiny, and the
+ * signal is private anyway.
*/
- if (!error && sig && p->sighand) {
- spin_lock_irq(&p->sighand->siglock);
+ if (!error && sig && lock_task_sighand(p, &flags)) {
error = specific_send_sig_info(sig, &info, p);
- spin_unlock_irq(&p->sighand->siglock);
+ unlock_task_sighand(p, &flags);
}
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
return error;
}