From: Alexander Sverdlin <alexander.sverdlin-OYasijW0DpE@public.gmane.org>
To: ext Alan Stern <stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz@public.gmane.org>
Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
"Eric W. Biederman"
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>,
Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>
Subject: Re: [PATCH] i2c: suppress lockdep warning on delete_device
Date: Fri, 17 May 2013 17:02:13 +0200 [thread overview]
Message-ID: <51964675.6030807@nsn.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1305171040580.1012-100000-IYeN2dnnYyZXsRXLowluHWD2FQJk+8+b@public.gmane.org>
Hi!
On 05/17/2013 04:42 PM, ext Alan Stern wrote:
>> i2c: suppress lockdep warning on delete_device
>>
>> Since commit 846f99749ab68bbc7f75c74fec305de675b1a1bf the following lockdep
>> warning is thrown in case i2c device is removed (via delete_device sysfs
>> attribute) which contains subdevices (e.g. i2c multiplexer):
>
> Can you explain this in a little more detail? Exactly what does the
> delete_device attribute do, when called for device D?
>
> That is, what does a write to /sys/bus/i2c/devices/D/delete_device do?
Like USB with its hubs, I2C structure could be tree-like, with I2C multiplexers.
delete_device attribute removes I2C device from the subsystem, which is usually not
a problem, except the case when device is a multiplexer and sub-devices should be
removed first. Here we have the problem: holding a "s_active" lock on
"delete_device" attribute of a parent (multiplexer) we need to delete children, but
they were created with the same static attribute "delete_device".
The safety of this operation is exactly the same as in USB case... Any more clever
lockdep annotation is exactly not so easy...
--
Best regards,
Alexander Sverdlin.
next prev parent reply other threads:[~2013-05-17 15:02 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-17 12:56 [PATCH] i2c: suppress lockdep warning on delete_device Alexander Sverdlin
[not found] ` <51962903.9050901-OYasijW0DpE@public.gmane.org>
2013-05-17 14:42 ` Alan Stern
[not found] ` <Pine.LNX.4.44L0.1305171040580.1012-100000-IYeN2dnnYyZXsRXLowluHWD2FQJk+8+b@public.gmane.org>
2013-05-17 15:02 ` Alexander Sverdlin [this message]
[not found] ` <51964675.6030807-OYasijW0DpE@public.gmane.org>
2013-05-17 15:31 ` Alan Stern
[not found] ` <Pine.LNX.4.44L0.1305171116500.1012-100000-IYeN2dnnYyZXsRXLowluHWD2FQJk+8+b@public.gmane.org>
2013-05-17 16:25 ` Alexander Sverdlin
[not found] ` <519659F7.90608-OYasijW0DpE@public.gmane.org>
2013-05-17 17:16 ` Alan Stern
2013-05-17 20:47 ` Wolfram Sang
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