[PATCH] kill_something_info: don't take tasklist_lock for pid==-1 case

Atsushi Tsuji
2008-03-25T04:27:44Z

Hi Oleg,

Thanks for some patches about tasklist_lock. The avoidance of
tasklist_lock is very important for us. And now, I found another
avoidable tasklist_lock, and made the patch. Could you please have a
look?

This patch avoid taking tasklist_lock in kill_something_info() when
the pid is -1. It can convert to rcu_read_lock() for this case because
group_send_sig_info() doesn't need tasklist_lock.

This patch is for 2.6.25-rc5-mm1.

Signed-off-by: Atsushi Tsuji <a-tsuji@bk.jp.nec.com>
---
diff --git a/kernel/signal.c b/kernel/signal.c
index 3edbfd4..a888c58 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1089,14 +1089,16 @@ static int kill_something_info(int sig, struct siginfo
*info, int pid)
return ret;
}

- read_lock(&tasklist_lock);
if (pid != -1) {
+ read_lock(&tasklist_lock);
ret = __kill_pgrp_info(sig, info,
pid ? find_vpid(-pid) : task_pgrp(current));
+ read_unlock(&tasklist_lock);
} else {
int retval = 0, count = 0;
struct task_struct * p;

+ rcu_read_lock();
for_each_process(p) {
if (p->pid > 1 && !same_thread_group(p, current)) {
int err = group_send_sig_info(sig, info, p);
@@ -1106,8 +1108,8 @@ static int kill_something_info(int sig, struct siginfo
*info, int pid)
}
}
ret = count ? retval : -ESRCH;
+ rcu_read_unlock();
}
- read_unlock(&tasklist_lock);

return ret;
}