linux-kernel - [PATCH] hrtimer: prevent migration for raising softirq

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <Pine.LNX.4.58.0807031428440.7798@gandalf.stny.rr.com>
Date:	Thu, 3 Jul 2008 14:31:26 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>, akpm@...l.org,
	Peter Zijlstra <peterz@...radead.org>, stable@...nel.org
Subject: [PATCH] hrtimer: prevent migration for raising softirq


Due to a possible deadlock, the waking of the softirq was pushed outside
of the hrtimer base locks. See commit 0c96c5979a522c3323c30a078a70120e29b5bdbc

Unfortunately this allows the task to migrate after setting up the softirq
and raising it. Since softirqs run a queue that is per-cpu we may raise the
softirq on the wrong CPU and this will keep the queued softirq task from
running.

To solve this issue, this patch disables preemption around the releasing
of the hrtimer lock and raising of the softirq.

Signed-off-by: Steven Rostedt <srostedt@...hat.com>

---
 kernel/hrtimer.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linus.git/kernel/hrtimer.c
===================================================================
--- linus.git.orig/kernel/hrtimer.c	2008-05-09 15:11:45.000000000 -0400
+++ linus.git/kernel/hrtimer.c	2008-07-03 14:07:30.000000000 -0400
@@ -1003,10 +1003,18 @@ hrtimer_start(struct hrtimer *timer, kti
 	 */
 	raise = timer->state == HRTIMER_STATE_PENDING;

+	/*
+	 * We use preempt_disable to prevent this task from migrating after
+	 * setting up the softirq and raising it. Otherwise, if me migrate
+	 * we will raise the softirq on the wrong CPU.
+	 */
+	preempt_disable();
+
 	unlock_hrtimer_base(timer, &flags);

 	if (raise)
 		hrtimer_raise_softirq();
+	preempt_enable();

 	return ret;
 }

--
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/