This is a note to let you know that I've just added the patch titled
genirq: Remove racy waitqueue_active check
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
genirq-remove-racy-waitqueue_active-check.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c685689fd24d310343ac33942e9a54a974ae9c43 Mon Sep 17 00:00:00 2001
From: Chuansheng Liu <chuansheng.liu@xxxxxxxxx>
Date: Mon, 24 Feb 2014 11:29:50 +0800
Subject: genirq: Remove racy waitqueue_active check
From: Chuansheng Liu <chuansheng.liu@xxxxxxxxx>
commit c685689fd24d310343ac33942e9a54a974ae9c43 upstream.
We hit one rare case below:
T1 calling disable_irq(), but hanging at synchronize_irq()
always;
The corresponding irq thread is in sleeping state;
And all CPUs are in idle state;
After analysis, we found there is one possible scenerio which
causes T1 is waiting there forever:
CPU0 CPU1
synchronize_irq()
wait_event()
spin_lock()
atomic_dec_and_test(&threads_active)
insert the __wait into queue
spin_unlock()
if(waitqueue_active)
atomic_read(&threads_active)
wake_up()
Here after inserted the __wait into queue on CPU0, and before
test if queue is empty on CPU1, there is no barrier, it maybe
cause it is not visible for CPU1 immediately, although CPU0 has
updated the queue list.
It is similar for CPU0 atomic_read() threads_active also.
So we'd need one smp_mb() before waitqueue_active.that, but removing
the waitqueue_active() check solves it as wel l and it makes
things simple and clear.
Signed-off-by: Chuansheng Liu <chuansheng.liu@xxxxxxxxx>
Cc: Xiaoming Wang <xiaoming.wang@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1393212590-32543-1-git-send-email-chuansheng.liu@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/irq/manage.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -777,8 +777,7 @@ static irqreturn_t irq_thread_fn(struct
static void wake_threads_waitq(struct irq_desc *desc)
{
- if (atomic_dec_and_test(&desc->threads_active) &&
- waitqueue_active(&desc->wait_for_threads))
+ if (atomic_dec_and_test(&desc->threads_active))
wake_up(&desc->wait_for_threads);
}
Patches currently in stable-queue which might be from chuansheng.liu@xxxxxxxxx are
queue-3.4/genirq-remove-racy-waitqueue_active-check.patch
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