On 10/20/16 17:20, Jiri Slaby wrote:
> commit 2a708cff93f1845b9239bc7d6310aef54e716c6a upstream.
>
> __dm_destroy() takes io_barrier SRCU lock (dm_get_live_table) and
> suspend_lock in reverse order. Doing so can cause AB-BA deadlock:
>
> __dm_destroy dm_swap_table
> ---------------------------------------------------
> mutex_lock(suspend_lock)
> dm_get_live_table()
> srcu_read_lock(io_barrier)
> dm_sync_table()
> synchronize_srcu(io_barrier)
> .. waiting for dm_put_live_table()
> mutex_lock(suspend_lock)
> .. waiting for suspend_lock
>
> Fix this by taking the locks in proper order.
>
> Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
> Fixes: ab7c7bb6f4ab ("dm: hold suspend_lock while suspending device during device deletion")
> Acked-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
> ---
> drivers/md/dm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 5a0b1742f794..de444d3ae293 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -2444,14 +2444,14 @@ static void __dm_destroy(struct mapped_device *md, bool wait)
> * do not race with internal suspend.
> */
> mutex_lock(&md->suspend_lock);
> + map = dm_get_live_table(md, &srcu_idx);
> if (!dm_suspended_md(md)) {
> dm_table_presuspend_targets(map);
> dm_table_postsuspend_targets(map);
> }
> - mutex_unlock(&md->suspend_lock);
> -
> /* dm_put_live_table must be before msleep, otherwise deadlock is possible */
> dm_put_live_table(md, srcu_idx);
> + mutex_unlock(&md->suspend_lock);
>
> /*
> * Rare, but there may be I/O requests still going to complete,
I don't have 3.12-stable tree at hand but this patch looks incorrect.
The patch misses the part of upstream patch that removes existing
dm_get_live_table(). By just adding dm_get_live_table(), you will
have unbalanced numbers of get and put and break refcounting of md.
--
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.
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