[Ocfs2-devel] [PATCH 1/2 v3] ocfs2/dlm: fix race between convert and recovery

[Junxiao Bi]

On 09/24/2015 11:14 AM, Joseph Qi wrote:
> There is a race window between dlmconvert_remote and
> dlm_move_lockres_to_recovery_list, which will cause a lock with
> OCFS2_LOCK_BUSY in grant list, thus system hangs.
> 
> dlmconvert_remote
> {
>         spin_lock(&res->spinlock);
>         list_move_tail(&lock->list, &res->converting);
>         lock->convert_pending = 1;
>         spin_unlock(&res->spinlock);
> 
>         status = dlm_send_remote_convert_request();
>         >>>>>> race window, master has queued ast and return DLM_NORMAL,
>                and then down before sending ast.
>                this node detects master down and calls
>                dlm_move_lockres_to_recovery_list, which will revert the
>                lock to grant list.
>                Then OCFS2_LOCK_BUSY won't be cleared as new master won't
>                send ast any more because it thinks already be authorized.
How this race windowed fixed?
the process have sent convert request to master node successfully(return
value DLM_NORMAL) then wait on LOCK_BUSY, then when master node panic
before send out ast, dlm_move_lockres_to_recovery_list() move the lock
to grant list. Ast never come.

Thanks,
Junxiao.

> 
>         spin_lock(&res->spinlock);
>         lock->convert_pending = 0;
>         if (status != DLM_NORMAL)
>                 dlm_revert_pending_convert(res, lock);
>         spin_unlock(&res->spinlock);
> }
> 
> In this case, check if res->state has DLM_LOCK_RES_RECOVERING bit set
> (res is still in recovering) or res master changed (new master has
> finished recovery), reset the status to DLM_RECOVERING, then it will
> retry convert.
> 
> Signed-off-by: Joseph Qi <joseph.qi at huawei.com>
> Reported-by: Yiwen Jiang <jiangyiwen at huawei.com>
> Cc: <stable at vger.kernel.org>
> ---
>  fs/ocfs2/dlm/dlmconvert.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/dlm/dlmconvert.c b/fs/ocfs2/dlm/dlmconvert.c
> index e36d63f..9e6116e 100644
> --- a/fs/ocfs2/dlm/dlmconvert.c
> +++ b/fs/ocfs2/dlm/dlmconvert.c
> @@ -262,6 +262,7 @@ enum dlm_status dlmconvert_remote(struct dlm_ctxt *dlm,
>  				  struct dlm_lock *lock, int flags, int type)
>  {
>  	enum dlm_status status;
> +	u8 old_owner = res->owner;
> 
>  	mlog(0, "type=%d, convert_type=%d, busy=%d\n", lock->ml.type,
>  	     lock->ml.convert_type, res->state & DLM_LOCK_RES_IN_PROGRESS);
> @@ -316,11 +317,19 @@ enum dlm_status dlmconvert_remote(struct dlm_ctxt *dlm,
>  	spin_lock(&res->spinlock);
>  	res->state &= ~DLM_LOCK_RES_IN_PROGRESS;
>  	lock->convert_pending = 0;
> -	/* if it failed, move it back to granted queue */
> +	/* if it failed, move it back to granted queue.
> +	 * if master returns DLM_NORMAL and then down before sending ast,
> +	 * it may have already been moved to granted queue, reset to
> +	 * DLM_RECOVERING and retry convert */
>  	if (status != DLM_NORMAL) {
>  		if (status != DLM_NOTQUEUED)
>  			dlm_error(status);
>  		dlm_revert_pending_convert(res, lock);
> +	} else if ((res->state & DLM_LOCK_RES_RECOVERING) ||
> +			(old_owner != res->owner)) {
> +		mlog(0, "res %.*s is in recovering or has been recovered.\n",
> +				res->lockname.len, res->lockname.name);
> +		status = DLM_RECOVERING;
>  	}
>  bail:
>  	spin_unlock(&res->spinlock);
>