On Thu, Mar 09, 2017 at 11:16:21AM +0100, Jan Kara wrote: > SCSI can call device_add_disk() several times for one request queue when > a device in unbound and bound, creating new gendisk each time. This will > lead to bdi being repeatedly registered and unregistered. This was not a > big problem until commit 165a5e22fafb "block: Move bdi_unregister() to > del_gendisk()" since bdi was only registered repeatedly (bdi_register() > handles repeated calls fine, only we ended up leaking reference to > gendisk due to overwriting bdi->owner) but unregistered only in > blk_cleanup_queue() which didn't get called repeatedly. After > 165a5e22fafb we were doing correct bdi_register() - bdi_unregister() > cycles however bdi_unregister() is not prepared for it. So make sure > bdi_unregister() cleans up bdi in such a way that it is prepared for > a possible following bdi_register() call. > > An easy way to provoke this behavior is to enable > CONFIG_DEBUG_TEST_DRIVER_REMOVE and use scsi_debug driver to create a > scsi disk which immediately hangs without this fix. > > Fixes: 165a5e22fafb127ecb5914e12e8c32a1f0d3f820 > Tested-by: Omar Sandoval <osandov@xxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Thanks! -- tejun
