linux-kernel - [PATCH 3/5] blktrace: refcount the request

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Date:   Tue, 14 Apr 2020 04:19:00 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     axboe@...nel.dk, viro@...iv.linux.org.uk, bvanassche@....org,
        gregkh@...uxfoundation.org, rostedt@...dmis.org, mingo@...hat.com,
        jack@...e.cz, ming.lei@...hat.com, nstange@...e.de,
        akpm@...ux-foundation.org
Cc:     mhocko@...e.com, yukuai3@...wei.com, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
        Omar Sandoval <osandov@...com>,
        Hannes Reinecke <hare@...e.com>,
        Michal Hocko <mhocko@...nel.org>
Subject: [PATCH 3/5] blktrace: refcount the request_queue during ioctl

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@....org>
Cc: Omar Sandoval <osandov@...com>
Cc: Hannes Reinecke <hare@...e.com>
Cc: Nicolai Stange <nstange@...e.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: yu kuai <yukuai3@...wei.com>
Reviewed-by: Bart Van Assche <bvanassche@....org>
Signed-off-by: Luis Chamberlain <mcgrof@...nel.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