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From:   Luis Chamberlain <mcgrof@kernel.org>
To:     axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org,
        gregkh@linuxfoundation.org, rostedt@goodmis.org, mingo@redhat.com,
        jack@suse.cz, ming.lei@redhat.com, nstange@suse.de,
        akpm@linux-foundation.org
Cc:     mhocko@suse.com, yukuai3@huawei.com, linux-block@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Luis Chamberlain <mcgrof@kernel.org>,
        Omar Sandoval <osandov@fb.com>,
        Hannes Reinecke <hare@suse.com>,
        Michal Hocko <mhocko@kernel.org>
Subject: [PATCH 3/5] blktrace: refcount the request_queue during ioctl
Date:   Tue, 14 Apr 2020 04:19:00 +0000
Message-Id: <20200414041902.16769-4-mcgrof@kernel.org>
In-Reply-To: <20200414041902.16769-1-mcgrof@kernel.org>
References: <20200414041902.16769-1-mcgrof@kernel.org>
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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;
 }
 
-- 
2.25.1