On Mon, Feb 13, 2017 at 10:01:07PM +0100, Paolo Valente wrote: > If, at boot, a legacy I/O scheduler is chosen for a device using blk-mq, > or, viceversa, a blk-mq scheduler is chosen for a device using blk, then > that scheduler is set and initialized without any check, driving the > system into an inconsistent state. This commit addresses this issue by > letting elevator_get fail for these wrong cross choices. > > Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx> > --- > block/elevator.c | 26 ++++++++++++++++++-------- > 1 file changed, 18 insertions(+), 8 deletions(-) Hey, Paolo, How exactly are you triggering this? In __elevator_change(), we do check for mq or not mq: if (!e->uses_mq && q->mq_ops) { elevator_put(e); return -EINVAL; } if (e->uses_mq && !q->mq_ops) { elevator_put(e); return -EINVAL; } We don't ever appear to call elevator_init() with a specific scheduler name, and for the default we switch off of q->mq_ops and use the defaults from Kconfig: if (q->mq_ops && q->nr_hw_queues == 1) e = elevator_get(CONFIG_DEFAULT_SQ_IOSCHED, false); else if (q->mq_ops) e = elevator_get(CONFIG_DEFAULT_MQ_IOSCHED, false); else e = elevator_get(CONFIG_DEFAULT_IOSCHED, false); if (!e) { printk(KERN_ERR "Default I/O scheduler not found. " \ "Using noop/none.\n"); e = elevator_get("noop", false); } So I guess this could happen if someone manually changed those Kconfig options, but I don't see what other case would make this happen, could you please explain?