[PATCH v2] genirq: don't sync irq thread if current happen to be the very irq thread

[Yong Zhang <yong.zhang0@gmail.com>]

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@windriver.com>
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@gmail.com>
Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
---
 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