Re: [patch/rft 2.6.26-rc1] i2c-core: stop using i2c_adapter.clients

[David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>]

On Tuesday 20 May 2008, Jean Delvare wrote:
> I remember doing the same change several months ago, but finally
> dropping the patch because it was deadlocking. Your patch has the exact
> same problem: rmmod'ing a legacy i2c driver deadlocks.

I thought that had been resolved as part of another patch
resolving a self-deadlock ... I guess not!  I'll have to
set up a test rig with a legacy driver module, I guess.


I'll have a closer look at this.  This wait-for-completion
hook is clearly an abuse of the driver model code, but it
might be practical to solve it by upping refcounts for legacy
code and having a list of pending deletes.

Did lockdep tell you more about locking goofage here, or
is this the only symptiom?


> rmmod         D ffffffff80443380     0  4669   4652
>  ffff81002e177cc8 0000000000000086 ffff81002e1dc190 ffff81003f8a1240
>  ffff81002e177cc8 ffff81002e177cc8 ffff81002e226b90 7fffffffffffffff
>  0000000000000002 7fffffffffffffff ffff81003f172648 ffff81002e177d48
> Call Trace:
>  [<ffffffff8042c175>] schedule_timeout+0x95/0xd0
>  [<ffffffff802c3ce0>] ? sysfs_remove_dir+0x60/0x80
>  [<ffffffff8042bf31>] wait_for_common+0xd1/0x160
>  [<ffffffff80225080>] ? default_wake_function+0x0/0x10
>  [<ffffffff8030d4e7>] ? kobject_put+0x27/0x60
>  [<ffffffff8042c058>] wait_for_completion+0x18/0x20
>  [<ffffffff803b4fe2>] i2c_detach_client+0x82/0xc0
>  [<ffffffffa02e4071>] :lm90:lm90_detach_client+0x71/0x90
>  [<ffffffff803b4f0b>] i2c_do_detach_client+0x8b/0xe0
>  [<ffffffff803b4e80>] ? i2c_do_detach_client+0x0/0xe0
>  [<ffffffff8038d473>] device_for_each_child+0x33/0x60
>  [<ffffffff803b45e6>] i2c_del_driver+0x106/0x120
>  [<ffffffffa02e4f10>] :lm90:sensors_lm90_exit+0x10/0x12
>  [<ffffffff8024d41e>] sys_delete_module+0x12e/0x1f0
>  [<ffffffff8020b43b>] system_call_after_swapgs+0x7b/0x80
> 
> I even seem to remember that you had been able to explain this deadlock
> back then...

Yeah, that's why I have various i2c lock removal patches
floating around.


> Obviously I can't take your patch until this is solved.



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