[Ocfs2-devel] [PATCH] ocfs2/cluster: unlock the o2hb_live_lock before the o2nm_depend_item()

[Joseph Qi <jiangqi903@gmail.com>]

Hi Alex,

On 17/10/31 20:41, alex chen wrote:
> In the following situation, the down_write() will be called under
> the spin_lock(), which may lead a soft lockup:
> o2hb_region_inc_user
>  spin_lock(&o2hb_live_lock)
>   o2hb_region_pin
>    o2nm_depend_item
>     configfs_depend_item
>      inode_lock
>       down_write
>       -->here may sleep and reschedule
> 
> So we should unlock the o2hb_live_lock before the o2nm_depend_item(), and
> get item reference in advance to prevent the region to be released.
> 
> Signed-off-by: Alex Chen <alex.chen@huawei.com>
> Reviewed-by: Yiwen Jiang <jiangyiwen@huawei.com>
> Reviewed-by: Jun Piao <piaojun@huawei.com>
> ---
>  fs/ocfs2/cluster/heartbeat.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ocfs2/cluster/heartbeat.c b/fs/ocfs2/cluster/heartbeat.c
> index d020604..f1142a9 100644
> --- a/fs/ocfs2/cluster/heartbeat.c
> +++ b/fs/ocfs2/cluster/heartbeat.c
> @@ -2399,6 +2399,9 @@ static int o2hb_region_pin(const char *region_uuid)
>  		if (reg->hr_item_pinned || reg->hr_item_dropped)
>  			goto skip_pin;
> 
> +		config_item_get(&reg->hr_item);
> +		spin_unlock(&o2hb_live_lock);
> +
If unlock here, the iteration of o2hb_all_regions is no longer safe.

Thanks,
Joseph

>  		/* Ignore ENOENT only for local hb (userdlm domain) */
>  		ret = o2nm_depend_item(&reg->hr_item);
>  		if (!ret) {
> @@ -2410,9 +2413,14 @@ static int o2hb_region_pin(const char *region_uuid)
>  			else {
>  				mlog(ML_ERROR, "Pin region %s fails with %d\n",
>  				     uuid, ret);
> +				config_item_put(&reg->hr_item);
> +				spin_lock(&o2hb_live_lock);
>  				break;
>  			}
>  		}
> +
> +		config_item_put(&reg->hr_item);
> +		spin_lock(&o2hb_live_lock);
>  skip_pin:
>  		if (found)
>  			break;
> -- 1.9.5.msysgit.1
> 
>