On Thu, Feb 22, 2018 at 10:25:28AM +0800, Joseph Qi wrote: > Hi Bart, > > Sorry for the delayed response since I was on holiday. > > On 18/2/10 02:44, Bart Van Assche wrote: > > Avoid that the following race can occur: > > > > blk_cleanup_queue() blkcg_print_blkgs() > > spin_lock_irq(lock) (1) spin_lock_irq(blkg->q->queue_lock) (2,5) > > q->queue_lock = &q->__queue_lock (3) > > spin_unlock_irq(lock) (4) > > spin_unlock_irq(blkg->q->queue_lock) (6) > > > > (1) take driver lock; > > (2) busy loop for driver lock; > > (3) override driver lock with internal lock; > > (4) unlock driver lock; > > (5) can take driver lock now; > > (6) but unlock internal lock. > > > > This change is safe because only the SCSI core and the NVME core keep > > a reference on a request queue after having called blk_cleanup_queue(). > > Neither driver accesses any of the removed data structures between its > > blk_cleanup_queue() and blk_put_queue() calls. > > > > Reported-by: Joseph Qi <[email protected]> > > Signed-off-by: Bart Van Assche <[email protected]> > > Cc: Jan Kara <[email protected]> > > --- > > block/blk-core.c | 31 +++++++++++++++++++++++++++++++ > > block/blk-sysfs.c | 7 ------- > > 2 files changed, 31 insertions(+), 7 deletions(-) > > > > diff --git a/block/blk-core.c b/block/blk-core.c > > index 41c74b37be85..6febc69a58aa 100644 > > --- a/block/blk-core.c > > +++ b/block/blk-core.c > > @@ -719,6 +719,37 @@ void blk_cleanup_queue(struct request_queue *q) > > del_timer_sync(&q->backing_dev_info->laptop_mode_wb_timer); > > blk_sync_queue(q); > > > > + /* > > + * I/O scheduler exit is only safe after the sysfs scheduler attribute > > + * has been removed. > > + */ > > + WARN_ON_ONCE(q->kobj.state_in_sysfs); > > + > I notice that several devices such as loop and zram will call > blk_cleanup_queue before del_gendisk, so it will hit this warning. Is > this normal?
In theory, it should be a bug to call del_gendisk() after blk_cleanup_queue() since dirty pages can't be flushed to device any more after queue is cleaned up. Thanks, Ming
