svn commit: r223061 - head/sys/kern

[Kostik Belousov]

On Mon, Jun 13, 2011 at 09:21:02PM +0000, Justin T. Gibbs wrote:
> Author: gibbs
> Date: Mon Jun 13 21:21:02 2011
> New Revision: 223061
> URL: http://svn.freebsd.org/changeset/base/223061
> 
> Log:
>   Fix a couple of race conditions in devstat(9) initialization.
>   
>   In devstat_new_entry(), there is no need to initialize the queue
>   and the mutex in this function.  There are ways to do static
>   initialization on both, so use STAILQ_HEAD_INITIALIZER and
>   MTX_SYSINIT to initialize the queue and the mutex.
>   
>   In devstat_alloc(), use an atomic test and set routine to guard
>   making our entry in /dev.  Using just a plain static variable
>   creates a race condition on multiprocessor machines.  If you
>   attempt to create a second entry in devfs, the kernel will panic.
Devfs returns an error if MAKEDEV_CHECKNAME flag is supplied and
attempt is made to create the existing node. The static guard is
still useful, since make_dev() call is costly, but you can remove
the atomic, since the race should be of limited scope.
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