2017-03-10 20:10:37

by Tahsin Erdogan

Subject: [PATCH] writeback: fix memory leak in wb_queue_work()

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 <[email protected]>
Signed-off-by: Tahsin Erdogan <[email protected]>
---
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

2017-03-13 14:23:20

by Jan Kara

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 <[email protected]>
> Signed-off-by: Tahsin Erdogan <[email protected]>

The patch looks good. You can add:

Reviewed-by: Jan Kara <[email protected]>

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 <[email protected]>
SUSE Labs, CR

2017-03-13 14:54:44

by Jens Axboe

Subject: Re: [PATCH] writeback: fix memory leak in wb_queue_work()

On 03/10/2017 01:09 PM, 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.

Added for 4.11, thanks Tahsin.

--
Jens Axboe