lkml.org 
[lkml]   [2009]   [Aug]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RT] Lockdep warning on boot with 2.6.31-rc5-rt1.1
On Sat, 8 Aug 2009, Ming Lei wrote:

> > The ordering requirement is: Don't try to acquire a device's lock if
> > you already hold the lock for a non-ancestor device.  More generally
> > (if more obscurely): If you already hold device A's lock, then don't
> > try to acquire the lock for device B unless you already hold the lock
> > for A & B's most recent common ancestor.
> >
>
> It seems that the following case is very common, and A and B have no
> common ancestor, but we can hold device A and B's lock at the same
> time, can't we?
>
> Thanks.
>
> device A comes in one bus:
> device_add()
> ->bus_attach_device()
> ->device_attach():drivers/base/dd.c /*holding device A's lock*/
> ->...drv->probe() /*sleep here some time*/

So right now thread 1 is sleeping.

> then device B comes in another bus:

So all this must happen in a different thread, thread 2:

> device_add()
> ->bus_attach_device()
> ->device_attach():drivers/base/dd.c /*holding device B's lock*/
> ->...drv->probe() /*sleep here some time*/

At this point, thread 1 holds A's lock and thread 2 holds B's lock.
Neither thread holds both locks.

Alan Stern

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2009-08-08 17:21    [W:0.062 / U:0.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site