[RFC v2 3/5] blktrace: ref count the request_queue during ioctl

[Luis Chamberlain <mcgrof@kernel.org>]

Ensure that the reqest_queue ref counts the request_queue
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 reqest_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>
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;
 }
 
-- 
2.25.1