James Bottomley [EMAIL PROTECTED] wrote: > On Fri, 2004-04-02 at 11:45, Mike Anderson wrote: > > Maybe some clarification here as I am unsure if we both think there > > needs to be a notification (a put call) from outside SCSI. We have > > release functions available on most objects in SCSI now. The issue is > > that when we register (add_disk, dev_set_drvdata, etc.) or pass a handle > > to another subsystem we need a reference count agreement to know when > > the other subsystem is done with the the object. Something like the > > put_device(parent) used in scsi_host_dev_release. > > Actually, no, that's not the issue here, if I understand you. The > reference counting model on the sdev->sdev_gendev seems to be working > correctly because sr.c takes a reference to the sdev_gendev on open and > drops it on close. > > The problem is that ULDs are implemented as struct device_drivers and as > such, their ->remove method gets called *not* on last put of sdev_gendev > but on device_del (when there are still active references).
The remove can do as much or as little as the implementor wishes, but I believe there is still a under lying issue here (see comment below). > > sr.c frees the cdinfo structure on ->remove, but still has its own > reference to sdev_gendev (because the device is still open). On final > close, the generic cdrom code tries to use cdinfo to close the device > and references a kfree'd structure. Really what sr.c wants to be doing > is freeing the cdinfo structure on last put, not on device_del. > Where does the last put come from? How do you close the open race or know when the final put_disk has been called? SCSI cannot do this alone as we have created and registered an object in another subsystem (alloc_disk and add_disk) and we have no indication when that objects ref count has reached zero. Or As I previous stated in the thread below I have the gendisk / block layer locking mis-understood and there is something that SCSI can do. For reference you can look at this thread sent by Alan about a sd race. http://marc.theaimsgroup.com/?t=107591185800003&r=1&w=2 While freeing in sr could be rearranged more like what sd does there is still the issue of a cross subsystem put to know that the ULDs open function will not be called again. -andmike -- Michael Anderson [EMAIL PROTECTED] ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
