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 <[email protected]>
--- 25/kernel/signal.c~2_TKILL_NO_TASKLIST 2008-03-07 10:47:02.000000000 +0300
+++ 25/kernel/signal.c 2008-03-07 12:20:34.000000000 +0300
@@ -2194,6 +2194,7 @@ static int do_tkill(int tgid, int pid, i
int error;
struct siginfo info;
struct task_struct *p;
+ unsigned long flags;
error = -ESRCH;
info.si_signo = sig;
@@ -2202,7 +2203,7 @@ static int do_tkill(int tgid, int pid, i
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);
@@ -2210,13 +2211,12 @@ static int do_tkill(int tgid, int pid, i
* The null signal is a permissions and process existence
* probe. No signal is actually delivered.
*/
- 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;
}