linux-kernel - Re: [PATCH] writeback: fix memory leak in wb_queue

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Date:   Mon, 13 Mar 2017 15:23:07 +0100
From:   Jan Kara <jack@...e.cz>
To:     Tahsin Erdogan <tahsin@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...com>,
        John Sperbeck <jsperbeck@...gle.com>,
        Peter Chang <dpf@...gle.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] writeback: fix memory leak in wb_queue_work()

On Fri 10-03-17 12:09:49, Tahsin Erdogan wrote:
> 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>

The patch looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/fs-writeback.c | 35 +++++++++++++++++++++--------------
>  1 file changed, 21 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index ef600591d96f..63ee2940775c 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -173,19 +173,33 @@ static void wb_wakeup(struct bdi_writeback *wb)
>  	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);
>  }
>  
> @@ -1873,16 +1887,9 @@ static long wb_do_writeback(struct bdi_writeback *wb)
>  
>  	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);
>  	}
>  
>  	/*
> -- 
> 2.12.0.246.ga2ecc84866-goog
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR