On Thu, 25 Feb 2010, Kiyoshi Ueda wrote: > Hi Mikulas, > > On 02/25/2010 07:33 AM +0900, Mikulas Patocka wrote: > >> Indeed, we shouldn't use the current dm_put() in any interrupt-context. > >> But the "mapped_device" can disappear in request-based dm while there > >> is a request after all bios complete, so I used dm_get()/dm_put() there. > >> I'll consider another way to prevent the problem without dm_get()/dm_put(). > >> E.g. wait for request completion in dm_put() instead. > > > > How can a request-in-progress exists when all the bios complete and the > > device is closed? > > In the current request-based dm, the device opener can remove > the mapped_device while the last request is still completing, > because bios in the last request complete first and then the device > opener can remove the mapped_device before the last request completes: > CPU0 CPU1 > ====================================================================== > <<INTERRUPT>> > blk_end_request_all(clone_rq) > blk_update_request(clone_rq) > bio_endio(clone_bio) == end_clone_bio > blk_update_request(orig_rq) > bio_endio(orig_bio) > <<I/O completed>> > dm_blk_close() > dev_remove() > dm_put(md) > <<Free md>> > blk_finish_request(clone_rq) > .... > dm_end_request(clone_rq) > free_rq_clone(clone_rq) > blk_end_request_all(orig_rq) > rq_completed(md) > > So we need a mechanism to defer the md deletion until the last request > completes. > > Thanks, > Kiyoshi Ueda Good point ... but I think this problem may happen even in normal non-request based dm. I don't know what to do with it. If one thread does: - bio_endio and another thread does: - close the device - remove the device - unload module - then the first thread, after bio_endio, executes non-existing instructions from unloaded module. Any ideas, how is it solved or how it should be solved? Module unloading does stop_machine, but AFAIK it waits for all CPUs to exit non-preemtable sections, it doesn't wait for the code to get out of disk request routine... Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
