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. Can you describe a bit more what the issue is to be addressed by this patch? Thanks, Ming