linux-kernel - Mysterious lockdep warning from the SCSI workqueue code

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Date:	Sat, 22 Dec 2007 11:27:32 -0600
From:	James Bottomley <James.Bottomley@...elEye.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Arjan van de Ven <arjan@...radead.org>
Subject: Mysterious lockdep warning from the SCSI workqueue code

I've no idea why this is occurring:

WARNING: at kernel/lockdep.c:700 look_up_lock_class()
Pid: 2068, comm: scsi_wq_3 Not tainted 2.6.24-rc6 #38
 [<c010535a>] show_trace_log_lvl+0x1a/0x30
 [<c0105ce2>] show_trace+0x12/0x20
 [<c010601c>] dump_stack+0x6c/0x80
 [<c014696d>] __lock_acquire+0x46d/0x10b0
 [<c0147628>] lock_acquire+0x78/0xa0
 [<c0136d18>] run_workqueue+0x128/0x1d0
 [<c013795c>] worker_thread+0x8c/0xf0
 [<c013ab32>] kthread+0x42/0x70
 [<c0104f47>] kernel_thread_helper+0x7/0x10
 =======================

it looks to be happening on the initial workqueue.c:run_workqueue()

	spin_lock_irq(&cwq->lock);

It's caused by lockdep.c:look_up_lock_class()

	WARN_ON_ONCE(class->name != lock->name);

but I'm not entirely sure what this actually means, not fully
understanding lockdep classes and how we acquire them in scsi.

James


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