On Sun, May 20, 2012 at 01:27:31PM +0800, Yong Zhang wrote:
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -41,6 +41,7 @@ early_param("threadirqs", setup_forced_irqthreads);
> void synchronize_irq(unsigned int irq)
> {
> struct irq_desc *desc = irq_to_desc(irq);
> + struct irqaction *action = desc->action;
Bad time for dereferencing *action.
---
From: Yong Zhang <yong.zhang@xxxxxxxxxxxxx>
Date: Sun, 20 May 2012 12:56:46 +0800
Subject: [PATCH v2] genirq: don't sync irq thread if current happen to be the very irq thread
Christophe reported against -rt http://marc.info/?l=linux-rt-users&m=133665600214984&w=2
BUG: scheduling while atomic: irq/37-s3c-mci/253/0x00000102
Modules linked in:
[<c000e9fc>] (unwind_backtrace+0x0/0x12c) from [<c029b82c>] (__schedule+0x58/0x2c0)
[<c029b82c>] (__schedule+0x58/0x2c0) from [<c029bc10>] (schedule+0x8c/0xb0)
[<c029bc10>] (schedule+0x8c/0xb0) from [<c0055614>] (synchronize_irq+0xbc/0xd8)
[<c0055614>] (synchronize_irq+0xbc/0xd8) from [<c01db6b0>] (pio_tasklet+0x34/0x11c)
[<c01db6b0>] (pio_tasklet+0x34/0x11c) from [<c0024914>] (__tasklet_action+0x68/0x80)
[<c0024914>] (__tasklet_action+0x68/0x80) from [<c0024ca4>] (__do_softirq+0x88/0x130)
[<c0024ca4>] (__do_softirq+0x88/0x130) from [<c0024ef0>] (do_softirq+0x48/0x54)
[<c0024ef0>] (do_softirq+0x48/0x54) from [<c0025048>] (local_bh_enable+0x8c/0xc0)
[<c0025048>] (local_bh_enable+0x8c/0xc0) from [<c0054678>] (irq_forced_thread_fn+0x4c/0x54)
[<c0054678>] (irq_forced_thread_fn+0x4c/0x54) from [<c0054454>] (irq_thread+0xa0/0x1c0)
[<c0054454>] (irq_thread+0xa0/0x1c0) from [<c0038628>] (kthread+0x84/0x8c)
[<c0038628>] (kthread+0x84/0x8c) from [<c000a100>] (kernel_thread_exit+0x0/0x8)
Whe looking at this issue, I find that there is a typical deadlock
scenario with forced treaded irq,
irq_forced_thread_fn()
local_bh_enable();
do_softirq();
disable_irq();
synchronize_irq();
wait_event();
/*DEAD*/
Cure it by unsync if current happen to be the very irq thread.
Reported-by: Christophe Huriaux <c.huriaux@xxxxxxxxx>
Signed-off-by: Yong Zhang <yong.zhang0@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/irq/manage.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 89a3ea8..7a48f74 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -41,6 +41,7 @@ early_param("threadirqs", setup_forced_irqthreads);
void synchronize_irq(unsigned int irq)
{
struct irq_desc *desc = irq_to_desc(irq);
+ struct irqaction *action;
bool inprogress;
if (!desc)
@@ -67,7 +68,16 @@ void synchronize_irq(unsigned int irq)
/*
* We made sure that no hardirq handler is running. Now verify
* that no threaded handlers are active.
+ * But for theaded irq, we don't sync if current happens to be
+ * the irq thread; otherwise we could deadlock.
*/
+ action = desc->action;
+ while (action) {
+ if (action->thread && action->thread == current)
+ return;
+ action = action->next;
+ }
+
wait_event(desc->wait_for_threads, !atomic_read(&desc->threads_active));
}
EXPORT_SYMBOL(synchronize_irq);
--
1.7.1
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