Messages in this thread Patch in this message | | | Date | Thu, 16 Apr 2020 10:31:22 +0800 | From | Ming Lei <> | Subject | Re: [PATCH 3/5] blktrace: refcount the request_queue during ioctl |
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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@acm.org> > Cc: Omar Sandoval <osandov@fb.com> > Cc: Hannes Reinecke <hare@suse.com> > Cc: Nicolai Stange <nstange@suse.de> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Michal Hocko <mhocko@kernel.org> > Cc: yu kuai <yukuai3@huawei.com> > Reviewed-by: Bart Van Assche <bvanassche@acm.org> > Signed-off-by: Luis Chamberlain <mcgrof@kernel.org> > --- > 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
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