On Aug 8, 2012, at 4:42 AM, Fubo Chen <fubo.c...@gmail.com> wrote:

> Anyone seen this before ? Also occurs with 3.4.1.
> ======================================================
> [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
> 3.6.0-rc1-debug+ #1 Not tainted
> ------------------------------------------------------
> swapper/1/0 [HC0[0]:SC1[1]:HE0:SE0] is trying to acquire:
> (&(&session->lock)->rlock){+.-...}, at: [<ffffffffa025dc08>]
> iscsi_eh_cmd_timed_out+0x58/0x2e0 [libiscsi]
> and this task is already holding:
> (&(&q->__queue_lock)->rlock){-.-...}, at: [<ffffffff811f6965>]
> blk_rq_timed_out_timer+0x25/0x140
> which would create a new lock dependency:
> (&(&q->__queue_lock)->rlock){-.-...} -> (&(&session->lock)->rlock){+.-...}
> but this new dependency connects a HARDIRQ-irq-safe lock:
> (&(&q->__queue_lock)->rlock){-.-...}
> ... which became HARDIRQ-irq-safe at:
>  [<ffffffff8109b5ca>] __lock_acquire+0x7ea/0x1ba0
>  [<ffffffff8109cfc2>] lock_acquire+0x92/0x140
>  [<ffffffff814b41c5>] _raw_spin_lock_irqsave+0x65/0xb0
>  [<ffffffff812e2974>] blk_done+0x34/0x110
>  [<ffffffff81295889>] vring_interrupt+0x49/0xc0
>  [<ffffffff810c68f5>] handle_irq_event_percpu+0x75/0x270
>  [<ffffffff810c6b38>] handle_irq_event+0x48/0x70
>  [<ffffffff810c9477>] handle_edge_irq+0x77/0x110
>  [<ffffffff81004042>] handle_irq+0x22/0x40
>  [<ffffffff814bda2a>] do_IRQ+0x5a/0xe0
>  [<ffffffff814b436f>] ret_from_intr+0x0/0x1a
>  [<ffffffff8100a7da>] default_idle+0x4a/0x170
>  [<ffffffff8100b609>] cpu_idle+0xe9/0x130
>  [<ffffffff814a4c6e>] start_secondary+0x26a/0x26c

Does this error only occur when using some sort of virt setup?

I do not think we will hit this with iscsi, because we do not ever grab the 
queue lock for a iscsi device from hard irq context. It is always done from 
softirq or thread context. The snippet above seems to be from the virtio_blk.c 

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