[Ocfs2-devel] [PATCH] ocfs2/dlm: avoid incorrect bit set in refmap on recovery master

[Srinivas Eeda <srinivas.eeda@oracle.com>]

thanks for making this patch, it looks good just few minor changes about 
comments

On 7/23/2010 5:15 AM, Wengang Wang wrote:
> In the following situation, there remains an incorrect bit in refmap on the
> recovery master. Finally the recovery master will fail at purging the lockres
> due to the incorrect bit in refmap.
>
> 1) node A has no interest on lockres A any longer, so it is purging it.
> 2) the owner of lockres A is node B, so node A is sending de-ref message
> to node B.
> 3) at this time, node B crashed. node C becomes the recovery master. it recovers
> lockres A(because the master is the dead node B).
> 4) node A migrated lockres A to node C with a refbit there.
> 5) node A failed to send de-ref message to node B because it crashed. The failure
> is ignored. no other action is done for lockres A any more.
>
> For mormal, re-send the deref message to it to recovery master can fix it. Well,
> ignoring the failure of deref to the original master and not recovering the lockres
> to recovery master has the same effect. And the later is simpler.
>
> Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
> ---
>  fs/ocfs2/dlm/dlmrecovery.c |   17 +++++++++++++++--
>  fs/ocfs2/dlm/dlmthread.c   |   28 +++++++++++++++++-----------
>  2 files changed, 32 insertions(+), 13 deletions(-)
>
> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> index 9dfaac7..06640f6 100644
> --- a/fs/ocfs2/dlm/dlmrecovery.c
> +++ b/fs/ocfs2/dlm/dlmrecovery.c
> @@ -1997,6 +1997,8 @@ void dlm_move_lockres_to_recovery_list(struct dlm_ctxt *dlm,
>  	struct list_head *queue;
>  	struct dlm_lock *lock, *next;
>  
> +	assert_spin_locked(&dlm->spinlock);
> +	assert_spin_locked(&res->spinlock);
>  	res->state |= DLM_LOCK_RES_RECOVERING;
>  	if (!list_empty(&res->recovering)) {
>  		mlog(0,
> @@ -2336,9 +2338,20 @@ static void dlm_do_local_recovery_cleanup(struct dlm_ctxt *dlm, u8 dead_node)
>  
>  				/* the wake_up for this will happen when the
>  				 * RECOVERING flag is dropped later */
>   
remove above comment as it doesn't seem to be relevant anymore.
> -				res->state &= ~DLM_LOCK_RES_DROPPING_REF;
> +				if (res->state & DLM_LOCK_RES_DROPPING_REF) {
> +					/*
> +					 * don't migrate a lockres which is in
> +					 * progress of dropping ref
> +					 */
>   
move this comment to before the if condition
> +					mlog(ML_NOTICE, "%.*s ignored for "
> +					     "migration\n", res->lockname.len,
> +					     res->lockname.name);
>   
This information only helps us in diagnosing any related issue and is 
not helpful in normal cases. So it should be 0 instead of ML_NOTICE.
> +					res->state &=
> +						~DLM_LOCK_RES_DROPPING_REF;
>   
we don't need to clear this state as dlm_purge_lockres removes it.
> +				} else
> +					dlm_move_lockres_to_recovery_list(dlm,
> +									  res);
>  
> -				dlm_move_lockres_to_recovery_list(dlm, res);
>  			} else if (res->owner == dlm->node_num) {
>  				dlm_free_dead_locks(dlm, res, dead_node);
>  				__dlm_lockres_calc_usage(dlm, res);
> diff --git a/fs/ocfs2/dlm/dlmthread.c b/fs/ocfs2/dlm/dlmthread.c
> index dd78ca3..47420ce 100644
> --- a/fs/ocfs2/dlm/dlmthread.c
> +++ b/fs/ocfs2/dlm/dlmthread.c
> @@ -92,17 +92,23 @@ int __dlm_lockres_has_locks(struct dlm_lock_resource *res)
>   * truly ready to be freed. */
>  int __dlm_lockres_unused(struct dlm_lock_resource *res)
>  {
> -	if (!__dlm_lockres_has_locks(res) &&
> -	    (list_empty(&res->dirty) && !(res->state & DLM_LOCK_RES_DIRTY))) {
> -		/* try not to scan the bitmap unless the first two
> -		 * conditions are already true */
> -		int bit = find_next_bit(res->refmap, O2NM_MAX_NODES, 0);
> -		if (bit >= O2NM_MAX_NODES) {
> -			/* since the bit for dlm->node_num is not
> -			 * set, inflight_locks better be zero */
> -			BUG_ON(res->inflight_locks != 0);
> -			return 1;
> -		}
> +	int bit;
> +
> +	if (__dlm_lockres_has_locks(res))
> +		return 0;
> +
> +	if (!list_empty(&res->dirty) || res->state & DLM_LOCK_RES_DIRTY)
> +		return 0;
> +
> +	if (res->state & DLM_LOCK_RES_RECOVERING)
> +		return 0;
> +
> +	bit = find_next_bit(res->refmap, O2NM_MAX_NODES, 0);
> +	if (bit >= O2NM_MAX_NODES) {
> +		/* since the bit for dlm->node_num is not
> +		 * set, inflight_locks better be zero */
> +		BUG_ON(res->inflight_locks != 0);
> +		return 1;
>  	}
>  	return 0;
>  }
>