[Ocfs2-devel] [PATCH] ocfs2/dlm: retry migrating if nomem or lockres is in recovery on target

[Sunil Mushran <sunil.mushran@oracle.com>]

I don't think this fixes the issue. As in, the fix for reco+mig race is a
lot more involved. Is someone hitting this freq? As in, this should be
a hard race to reproduce.

On 08/31/2010 08:41 AM, Wengang Wang wrote:
> This patch tries to fix two problems:
>
> problem 1):
> It's a case of recovery + migration. That is a recovery is happening when node I
> is in progress of umount. Node I is the recovery master.
> Say lockres A was mastered by the dead node and need to be recovered. Node I(the
> reco master) and node II both have reference on lockres A.
> So lockres A is being recovered from node II to node I, with RECOVERING flag set.
> The umounting process is going on, it happened to be migrating lockres A to node
> II. Since recovery not finished yet(RECOVERING still set), node II reponds with
> -EFAULT to kill node I. Then node I killed its self(BUGON).
>
> There is a checking for recovery(on RECOVERING), but it droped res->spinlock and
> dlm->spinlock. So the checking does not help much enough.
>
> Since we have to drop any spinlock when we are sending migrate lockres(
> DLM_MIG_LOCKRES_MSG) message, we have to deal with above case.
>
> problem 2):
> In the same context of problem 1), -ENOMEM from target node can trigger an
> incorrect BUG() on the requester of "migrate lockres".
>
> The fix is when target node returns -EFAULT or -ENOMEM, we retry the migration(
> for umount).
> Though they are two separated problems, the fixes are in the same way. So I
> combined them together.
>
> Signed-off-by: Wengang Wang<wen.gang.wang@oracle.com>
> ---
>   fs/ocfs2/dlm/dlmrecovery.c |   28 ++++++++++++++++++++++------
>   1 files changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> index aaaffbc..b7dd03f 100644
> --- a/fs/ocfs2/dlm/dlmrecovery.c
> +++ b/fs/ocfs2/dlm/dlmrecovery.c
> @@ -1122,6 +1122,8 @@ static int dlm_send_mig_lockres_msg(struct dlm_ctxt *dlm,
>   	     orig_flags&  DLM_MRES_MIGRATION ? "migration" : "recovery",
>   	     send_to);
>
> +#define WAIT_FOR_NOMEM_MS 30
> +resend:
>   	/* send it */
>   	ret = o2net_send_message(DLM_MIG_LOCKRES_MSG, dlm->key, mres,
>   				 sz, send_to,&status);
> @@ -1132,16 +1134,30 @@ static int dlm_send_mig_lockres_msg(struct dlm_ctxt *dlm,
>   		     "0x%x) to node %u\n", ret, DLM_MIG_LOCKRES_MSG,
>   		     dlm->key, send_to);
>   	} else {
> -		/* might get an -ENOMEM back here */
> -		ret = status;
>   		if (ret<  0) {
>   			mlog_errno(ret);
>
> -			if (ret == -EFAULT) {
> -				mlog(ML_ERROR, "node %u told me to kill "
> -				     "myself!\n", send_to);
> -				BUG();
> +			/*
> +			 * -ENOMEM or -EFAULT here.
> +			 * -EFAULT means lockres is in recovery.
> +			 * we should retry in both the two cases.
> +			 */
> +			ret = status;
> +			if (ret == -ENOMEM) {
> +				mlog(ML_NOTICE, "node %u no memory\n",
> +				     send_to);
> +				if (dlm_in_recovery(dlm)) {
> +					dlm_wait_for_recovery(dlm);
> +				} else {
> +					msleep(WAIT_FOR_NOMEM_MS);
> +				}
> +			} else {
> +				BUG_ON(ret != -EFAULT);
> +				mlog(ML_NOTICE, "node %u in recovery\n",
> +				     send_to);
> +				dlm_wait_for_recovery(dlm);
>   			}
> +			goto resend;
>   		}
>   	}
>
>