Re: orinoco driver causes *lots* of lockdep spew

From: Arjan van de Ven
Date: Thu Aug 03 2006 - 08:14:59 EST

On Wed, 2006-08-02 at 17:59 -0400, Dave Jones wrote:
> Wow. Nearly 400 lines of debug spew, from a simple 'ifup eth1'.
> Dave
> ADDRCONF(NETDEV_UP): eth1: link is not ready
> eth1: New link status: Disconnected (0002)
> ======================================================
> [ INFO: hard-safe -> hard-unsafe lock order detected ]
> ------------------------------------------------------
> events/0/5 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
> (af_callback_keys + sk->sk_family){-.--}, at: [<ffffffff802136b1>] sock_def_readable+0x19/0x6f
> and this task is already holding:
> (&priv->lock){++..}, at: [<ffffffff8824f70e>] orinoco_send_wevents+0x28/0x8b [orinoco]
> which would create a new lock dependency:
> (&priv->lock){++..} -> (af_callback_keys + sk->sk_family){-.--}

> [<ffffffff80267948>] _read_lock+0x28/0x34
> [<ffffffff802136b1>] sock_def_readable+0x19/0x6f
> [<ffffffff80259ad7>] netlink_broadcast+0x222/0x2e2
> [<ffffffff804287eb>] wireless_send_event+0x300/0x317
> [<ffffffff8824f732>] :orinoco:orinoco_send_wevents+0x4c/0x8b
> [<ffffffff8024f99c>] run_workqueue+0xa8/0xfb
> [<ffffffff8024c180>] worker_thread+0xef/0x122
> [<ffffffff80235437>] kthread+0x100/0x136
> [<ffffffff802613de>] child_rip+0x8/0x12

this is another one of those nasty buggers;

Lock A = the sk->sk_callback_lock
Lock B = priv->lock in the driver

Lock A is only BH safe
Lock B is hardirq safe and used in the hardirq

Cpu 0 cpu 1
user closes the netlink socket
takes lock B in orinoco_send_events
takes lock A in user context in netlink_release() (for write)
interrupt happens
takes lock B in hardirq handler (spins)

calls netlink_broadcast
which takes lock A for read (spins)

and you have a nice classical AB-BA deadlock

if you want to mail me at work (you don't), use arjan (at)

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