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> --- mm/backing-dev.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 6d861d090e9f..51325489aae5 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -710,6 +710,11 @@ static void cgwb_bdi_destroy(struct backing_dev_info *bdi) */ atomic_dec(&bdi->usage_cnt); wait_event(cgwb_release_wait, !atomic_read(&bdi->usage_cnt)); + /* + * Reinitialize usage_cnt so that we hold reference when @bdi gets + * re-registered. + */ + atomic_set(&bdi->usage_cnt, 1); } /** @@ -857,6 +862,8 @@ int bdi_register_owner(struct backing_dev_info *bdi, struct device *owner) MINOR(owner->devt)); if (rc) return rc; + /* Leaking owner reference... */ + WARN_ON(bdi->owner); bdi->owner = owner; get_device(owner); return 0; -- 2.10.2
