On Fri, Oct 7, 2011 at 12:49 AM, Greg KH <greg@xxxxxxxxx> wrote: > On Fri, Oct 07, 2011 at 10:33:07AM +0500, G, Manjunath Kondaiah wrote: >> +config PROBE_DEFER >> + bool "Deferred Driver Probe" >> + default y >> + help >> + This option provides deferring driver probe if it has dependency on >> + other driver. Without this feature, initcall ordering should be done >> + manually to resolve driver dependencies. This feature completely side >> + steps the issues by allowing driver registration to occur in any >> + order, and any driver can request to be retried after a few more other >> + drivers get probed. > > Why is this even an option? Why would you ever want it disabled? Why > does it need to be selected? > > If you are going to default something to 'y' then just make it so it > can't be turned off any other way by just not making it an option at > all. > > It also cleans up this diff a lot, as you really don't want #ifdef in .c > files. Okay, we'll drop the kconfig >> + * This bit is tricky. We want to process every device in the >> + * deferred list, but devices can be removed from the list at any >> + * time while inside this for-each loop. There are two things that >> + * need to be protected against: > > That's what the klist structure is supposed to make easier, why not use > that here? > >> + * - if the device is removed from the deferred_probe_list, then we >> + * loose our place in the loop. Since any device can be removed >> + * asynchronously, list_for_each_entry_safe() wouldn't make things >> + * much better. Simplest solution is to restart walking the list >> + * whenever the current device gets removed. Not the most efficient, >> + * but is simple to implement and easy to audit for correctness. >> + * - if the device is unregistered, and freed, then there is a risk >> + * of a null pointer dereference. This code uses get/put_device() >> + * to ensure the device cannot disappear from under our feet. > > Ick, use a klist, it was created to handle this exact problem in the > driver core, so to not use it would be wrong, right? This comment block is stale. I reworked the code before I handed it off to Manjunath, but I never rewrote the comment. The current code uses a pair of list to keep deferred devices separate from devices currently being probed, and the problem described above no longer exists. However, Manjunath and I will look into switching from the two list design to using klist. Thanks for the feedback. g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
