On Thu, Apr 16, 2020 at 10:31:22AM +0800, Ming Lei wrote: > On Tue, Apr 14, 2020 at 04:19:00AM +0000, Luis Chamberlain wrote: > > Ensure that the request_queue is refcounted during its full > > ioctl cycle. This avoids possible races against removal, given > > blk_get_queue() also checks to ensure the queue is not dying. > > > > This small race is possible if you defer removal of the request_queue > > and userspace fires off an ioctl for the device in the meantime. > > > > Cc: Bart Van Assche <bvanassche@xxxxxxx> > > Cc: Omar Sandoval <osandov@xxxxxx> > > Cc: Hannes Reinecke <hare@xxxxxxxx> > > Cc: Nicolai Stange <nstange@xxxxxxx> > > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > > Cc: yu kuai <yukuai3@xxxxxxxxxx> > > Reviewed-by: Bart Van Assche <bvanassche@xxxxxxx> > > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > > --- > > kernel/trace/blktrace.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c > > index 15086227592f..17e144d15779 100644 > > --- a/kernel/trace/blktrace.c > > +++ b/kernel/trace/blktrace.c > > @@ -701,6 +701,9 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg) > > if (!q) > > return -ENXIO; > > > > + if (!blk_get_queue(q)) > > + return -ENXIO; > > + > > mutex_lock(&q->blk_trace_mutex); > > > > switch (cmd) { > > @@ -729,6 +732,9 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg) > > } > > > > mutex_unlock(&q->blk_trace_mutex); > > + > > + blk_put_queue(q); > > + > > return ret; > > } > > Actually when bdev is opened, one extra refcount is held on gendisk, so > gendisk won't go away. And __device_add_disk() does grab one extra > refcount on request queue, so request queue shouldn't go away when ioctl > is running. Alright, then yes, this should not be needed. Luis