[Ocfs2-devel] [PATCH V2] ocfs2/dlm: fix a race between purge and migration

[Junxiao Bi <junxiao.bi@oracle.com>]

On 12/11/2015 11:09 AM, Xue jiufei wrote:
> We found a race between purge and migration when doing code review.  Node
> A put lockres to purgelist before receiving the migrate message from node
> B which is the master. Node A call dlm_mig_lockres_handler to handle
> this message.
> 
> dlm_mig_lockres_handler
>   dlm_lookup_lockres
>   >>>>>> race window, dlm_run_purge_list may run and send
>          deref message to master, waiting the response
>   spin_lock(&res->spinlock);
>   res->state |= DLM_LOCK_RES_MIGRATING;
>   spin_unlock(&res->spinlock);
>   dlm_mig_lockres_handler returns
> 
>   >>>>>> dlm_thread receives the response from master for the deref
>   message and triggers the BUG because the lockres has the state
>   DLM_LOCK_RES_MIGRATING with the following message:
> 
> dlm_purge_lockres:209 ERROR: 6633EB681FA7474A9C280A4E1A836F0F:
> res M0000000000000000030c0300000000 in use after deref
> 
> Signed-off-by: Jiufei Xue <xuejiufei@huawei.com>
> Reviewed-by: Joseph Qi <joseph.qi@huawei.com>
Looks good.
Reviewed-by: Junxiao Bi <junxiao.bi@oracle.com>
> ---
>  fs/ocfs2/dlm/dlmrecovery.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> index 58eaa5c..4055909 100644
> --- a/fs/ocfs2/dlm/dlmrecovery.c
> +++ b/fs/ocfs2/dlm/dlmrecovery.c
> @@ -1373,6 +1373,7 @@ int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data,
>  	char *buf = NULL;
>  	struct dlm_work_item *item = NULL;
>  	struct dlm_lock_resource *res = NULL;
> +	unsigned int hash;
>  
>  	if (!dlm_grab(dlm))
>  		return -EINVAL;
> @@ -1400,7 +1401,10 @@ int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data,
>  	/* lookup the lock to see if we have a secondary queue for this
>  	 * already...  just add the locks in and this will have its owner
>  	 * and RECOVERY flag changed when it completes. */
> -	res = dlm_lookup_lockres(dlm, mres->lockname, mres->lockname_len);
> +	hash = dlm_lockid_hash(mres->lockname, mres->lockname_len);
> +	spin_lock(&dlm->spinlock);
> +	res = __dlm_lookup_lockres(dlm, mres->lockname, mres->lockname_len,
> +			hash);
>  	if (res) {
>  	 	/* this will get a ref on res */
>  		/* mark it as recovering/migrating and hash it */
> @@ -1421,13 +1425,16 @@ int dlm_mig_lockres_handler(struct o2net_msg *msg, u32 len, void *data,
>  				     mres->lockname_len, mres->lockname);
>  				ret = -EFAULT;
>  				spin_unlock(&res->spinlock);
> +				spin_unlock(&dlm->spinlock);
>  				dlm_lockres_put(res);
>  				goto leave;
>  			}
>  			res->state |= DLM_LOCK_RES_MIGRATING;
>  		}
>  		spin_unlock(&res->spinlock);
> +		spin_unlock(&dlm->spinlock);
>  	} else {
> +		spin_unlock(&dlm->spinlock);
>  		/* need to allocate, just like if it was
>  		 * mastered here normally  */
>  		res = dlm_new_lockres(dlm, mres->lockname, mres->lockname_len);
>