linux-kernel - [PATCH 4.9 050/177] writeback: fix memory leak in wb_queue

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Message-Id: <20171218152912.507937104@linuxfoundation.org>
Date:   Mon, 18 Dec 2017 16:47:53 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, John Sperbeck <jsperbeck@...gle.com>,
        Tahsin Erdogan <tahsin@...gle.com>, Jan Kara <jack@...e.cz>,
        Jens Axboe <axboe@...com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.9 050/177] writeback: fix memory leak in wb_queue_work()

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tahsin Erdogan <tahsin@...gle.com>


[ Upstream commit 4a3a485b1ed0e109718cc8c9d094fa0f552de9b2 ]

When WB_registered flag is not set, wb_queue_work() skips queuing the
work, but does not perform the necessary clean up. In particular, if
work->auto_free is true, it should free the memory.

The leak condition can be reprouced by following these steps:

   mount /dev/sdb /mnt/sdb
   /* In qemu console: device_del sdb */
   umount /dev/sdb

Above will result in a wb_queue_work() call on an unregistered wb and
thus leak memory.

Reported-by: John Sperbeck <jsperbeck@...gle.com>
Signed-off-by: Tahsin Erdogan <tahsin@...gle.com>
Reviewed-by: Jan Kara <jack@...e.cz>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/fs-writeback.c |   35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -173,19 +173,33 @@ static void wb_wakeup(struct bdi_writeba
 	spin_unlock_bh(&wb->work_lock);
 }
 
+static void finish_writeback_work(struct bdi_writeback *wb,
+				  struct wb_writeback_work *work)
+{
+	struct wb_completion *done = work->done;
+
+	if (work->auto_free)
+		kfree(work);
+	if (done && atomic_dec_and_test(&done->cnt))
+		wake_up_all(&wb->bdi->wb_waitq);
+}
+
 static void wb_queue_work(struct bdi_writeback *wb,
 			  struct wb_writeback_work *work)
 {
 	trace_writeback_queue(wb, work);
 
-	spin_lock_bh(&wb->work_lock);
-	if (!test_bit(WB_registered, &wb->state))
-		goto out_unlock;
 	if (work->done)
 		atomic_inc(&work->done->cnt);
-	list_add_tail(&work->list, &wb->work_list);
-	mod_delayed_work(bdi_wq, &wb->dwork, 0);
-out_unlock:
+
+	spin_lock_bh(&wb->work_lock);
+
+	if (test_bit(WB_registered, &wb->state)) {
+		list_add_tail(&work->list, &wb->work_list);
+		mod_delayed_work(bdi_wq, &wb->dwork, 0);
+	} else
+		finish_writeback_work(wb, work);
+
 	spin_unlock_bh(&wb->work_lock);
 }
 
@@ -1875,16 +1889,9 @@ static long wb_do_writeback(struct bdi_w
 
 	set_bit(WB_writeback_running, &wb->state);
 	while ((work = get_next_work_item(wb)) != NULL) {
-		struct wb_completion *done = work->done;
-
 		trace_writeback_exec(wb, work);
-
 		wrote += wb_writeback(wb, work);
-
-		if (work->auto_free)
-			kfree(work);
-		if (done && atomic_dec_and_test(&done->cnt))
-			wake_up_all(&wb->bdi->wb_waitq);
+		finish_writeback_work(wb, work);
 	}
 
 	/*