On Thu, 2009-02-19 at 22:02 +0100, Thomas Hellstrom wrote: > > It looks to me like the driver preferred locking order is > > object_mutex (which happens to be the device global struct_mutex) > mmap_sem > offset_mutex. > > So if one could avoid using the struct_mutex for object bookkeeping (A > separate lock) then > vm_open() and vm_close() would adhere to that locking order as well, > simply by not taking the struct_mutex at all. > > So only fault() remains, in which that locking order is reversed. > Personally I think the trylock ->reschedule->retry method with proper > commenting is a good solution. It will be the _only_ place where locking > order is reversed and it is done in a deadlock-safe manner. Note that > fault() doesn't really fail, but requests a retry from user-space with > rescheduling to give the process holding the struct_mutex time to > release it.
It doesn't do the reschedule -- need_resched() will check if the current task was marked to be scheduled away, furthermore yield based locking sucks chunks. What's so very difficult about pulling the copy_*_user() out from under the locks? ------------------------------------------------------------------------------ Open Source Business Conference (OSBC), March 24-25, 2009, San Francisco, CA -OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise -Strategies to boost innovation and cut costs with open source participation -Receive a $600 discount off the registration fee with the source code: SFAD http://p.sf.net/sfu/XcvMzF8H -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
