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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