linux-kernel - [PATCH 3/3] child_wait_callback: check _

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [day] [month] [year] [list]

Date:	Thu, 2 Jul 2009 19:25:13 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Ratan Nalumasu <rnalumasu@...il.com>,
	Roland McGrath <roland@...hat.com>,
	Vitaly Mayatskikh <vmayatsk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] child_wait_callback: check __WNOTHREAD case

Suggested by Roland.

do_wait(__WNOTHREAD) can only succeed if the caller is either ptracer, or
it is ->real_parent and the child is not traced. IOW, caller == p->parent
otherwise we should not wake up.

Change child_wait_callback() to check this. Ratan reports the workload with
CPU load >99% caused by unnecessary wakeups, should be fixed by this patch.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---

 kernel/exit.c |    3 +++
 1 file changed, 3 insertions(+)

--- WAIT/kernel/exit.c~3_WNOTHREAD	2009-07-02 18:38:03.000000000 +0200
+++ WAIT/kernel/exit.c	2009-07-02 18:44:43.000000000 +0200
@@ -1569,6 +1569,9 @@ static int child_wait_callback(wait_queu
 	if (!eligible_child(wo, p))
 		return 0;
 
+	if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
+		return 0;
+
 	return default_wake_function(wait, mode, sync, key);
 }
 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/