[Ocfs2-devel] [PATCH 1/2] ocfs2 fix o2dlm dlm run purgelist

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

One way to skip a lockres in the purgelist is to list_del_init() and
list_add_tail(). That simplifies the patch a lot.

I have attached a quick & dirty patch. See if that satisfies all the
requirements.

Sunil

On 06/15/2010 09:43 PM, Srinivas Eeda wrote:
> There are two problems in dlm_run_purgelist
>
> 1. If a lockres is found to be in use, dlm_run_purgelist keeps trying to purge
> the same lockres instead of trying the next lockres.
>
> 2. When a lockres is found unused, dlm_run_purgelist releases lockres spinlock
> before setting DLM_LOCK_RES_DROPPING_REF and calls dlm_purge_lockres.
> spinlock is reacquired but in this window lockres can get reused. This leads
> to BUG.
>
> This patch modifies dlm_run_purgelist to skip lockres if it's in use and purge
>   next lockres. It also sets DLM_LOCK_RES_DROPPING_REF before releasing the
> lockres spinlock protecting it from getting reused.
>
> Signed-off-by: Srinivas Eeda<srinivas.eeda@oracle.com>
> ---
>   fs/ocfs2/dlm/dlmthread.c |  125 +++++++++++++++++++++++-----------------------
>   1 files changed, 63 insertions(+), 62 deletions(-)
>
> diff --git a/fs/ocfs2/dlm/dlmthread.c b/fs/ocfs2/dlm/dlmthread.c
> index 11a6d1f..fb0be6c 100644
> --- a/fs/ocfs2/dlm/dlmthread.c
> +++ b/fs/ocfs2/dlm/dlmthread.c
> @@ -158,39 +158,17 @@ static int dlm_purge_lockres(struct dlm_ctxt *dlm,
>   	int master;
>   	int ret = 0;
>
> -	spin_lock(&res->spinlock);
> -	if (!__dlm_lockres_unused(res)) {
> -		mlog(0, "%s:%.*s: tried to purge but not unused\n",
> -		     dlm->name, res->lockname.len, res->lockname.name);
> -		__dlm_print_one_lock_resource(res);
> -		spin_unlock(&res->spinlock);
> -		BUG();
> -	}
> -
> -	if (res->state&  DLM_LOCK_RES_MIGRATING) {
> -		mlog(0, "%s:%.*s: Delay dropref as this lockres is "
> -		     "being remastered\n", dlm->name, res->lockname.len,
> -		     res->lockname.name);
> -		/* Re-add the lockres to the end of the purge list */
> -		if (!list_empty(&res->purge)) {
> -			list_del_init(&res->purge);
> -			list_add_tail(&res->purge,&dlm->purge_list);
> -		}
> -		spin_unlock(&res->spinlock);
> -		return 0;
> -	}
> -
>   	master = (res->owner == dlm->node_num);
>
>   	if (!master)
>   		res->state |= DLM_LOCK_RES_DROPPING_REF;
> -	spin_unlock(&res->spinlock);
>
>   	mlog(0, "purging lockres %.*s, master = %d\n", res->lockname.len,
>   	     res->lockname.name, master);
>
>   	if (!master) {
>   		/* drop spinlock...  retake below */
> +		spin_unlock(&res->spinlock);
>   		spin_unlock(&dlm->spinlock);
>
>   		spin_lock(&res->spinlock);
> @@ -208,48 +186,37 @@ static int dlm_purge_lockres(struct dlm_ctxt *dlm,
>   		mlog(0, "%s:%.*s: dlm_deref_lockres returned %d\n",
>   		     dlm->name, res->lockname.len, res->lockname.name, ret);
>   		spin_lock(&dlm->spinlock);
> +		spin_lock(&res->spinlock);
>   	}
>
> -	spin_lock(&res->spinlock);
> -	if (!list_empty(&res->purge)) {
> -		mlog(0, "removing lockres %.*s:%p from purgelist, "
> -		     "master = %d\n", res->lockname.len, res->lockname.name,
> -		     res, master);
> -		list_del_init(&res->purge);
> -		spin_unlock(&res->spinlock);
> -		dlm_lockres_put(res);
> -		dlm->purge_count--;
> -	} else
> -		spin_unlock(&res->spinlock);
> -
> -	__dlm_unhash_lockres(res);
> -
>   	/* lockres is not in the hash now.  drop the flag and wake up
>   	 * any processes waiting in dlm_get_lock_resource. */
> -	if (!master) {
> -		spin_lock(&res->spinlock);
> +	if (!master)
>   		res->state&= ~DLM_LOCK_RES_DROPPING_REF;
> -		spin_unlock(&res->spinlock);
> -		wake_up(&res->wq);
> -	}
>   	return 0;
>   }
>
>   static void dlm_run_purge_list(struct dlm_ctxt *dlm,
>   			       int purge_now)
>   {
> -	unsigned int run_max, unused;
> +	unsigned int run_max;
>   	unsigned long purge_jiffies;
>   	struct dlm_lock_resource *lockres;
> +	struct dlm_lock_resource *nextres;
>
>   	spin_lock(&dlm->spinlock);
>   	run_max = dlm->purge_count;
>
> -	while(run_max&&  !list_empty(&dlm->purge_list)) {
> -		run_max--;
> +	if (list_empty(&dlm->purge_list)) {
> +		spin_unlock(&dlm->spinlock);
> +		return;
> +	}
> +
> +	lockres = list_entry(dlm->purge_list.next,
> +			     struct dlm_lock_resource, purge);
>
> -		lockres = list_entry(dlm->purge_list.next,
> -				     struct dlm_lock_resource, purge);
> +	while(run_max&&  lockres&&  !list_empty(&dlm->purge_list)) {
> +		run_max--;
>
>   		/* Status of the lockres *might* change so double
>   		 * check. If the lockres is unused, holding the dlm
> @@ -257,15 +224,12 @@ static void dlm_run_purge_list(struct dlm_ctxt *dlm,
>   		 * refs on it -- there's no need to keep the lockres
>   		 * spinlock. */
>   		spin_lock(&lockres->spinlock);
> -		unused = __dlm_lockres_unused(lockres);
> -		spin_unlock(&lockres->spinlock);
> -
> -		if (!unused)
> -			continue;
>
>   		purge_jiffies = lockres->last_used +
>   			msecs_to_jiffies(DLM_PURGE_INTERVAL_MS);
>
> +		mlog(0, "purging lockres %.*s\n", lockres->lockname.len,
> +		     lockres->lockname.name);
>   		/* Make sure that we want to be processing this guy at
>   		 * this time. */
>   		if (!purge_now&&  time_after(purge_jiffies, jiffies)) {
> @@ -273,20 +237,57 @@ static void dlm_run_purge_list(struct dlm_ctxt *dlm,
>   			 * in tail order, we can stop at the first
>   			 * unpurgable resource -- anyone added after
>   			 * him will have a greater last_used value */
> +			spin_unlock(&lockres->spinlock);
>   			break;
>   		}
>
> -		dlm_lockres_get(lockres);
> -
> +		/* If lockres is being used, or migrating purge next lockres */
> +		if (!__dlm_lockres_unused(lockres) ||
> +		    (lockres->state&  DLM_LOCK_RES_MIGRATING)) {
> +			if (!list_is_last(&lockres->purge,&dlm->purge_list))
> +				nextres = list_entry(lockres->purge.next,
> +					     struct dlm_lock_resource, purge);
> +			else
> +				nextres = NULL;
> +			spin_unlock(&lockres->spinlock);
> +			lockres = nextres;
> +			continue;
> +		}
> +		
>   		/* This may drop and reacquire the dlm spinlock if it
>   		 * has to do migration. */
> -		if (dlm_purge_lockres(dlm, lockres))
> -			BUG();
> -
> -		dlm_lockres_put(lockres);
> -
> -		/* Avoid adding any scheduling latencies */
> -		cond_resched_lock(&dlm->spinlock);
> +		dlm_purge_lockres(dlm, lockres);
> +		
> +		/* before we free the lockres we get the next lockres */
> +		if (list_empty(&lockres->purge))
> +			/* Shouldn't be in this state. Start from beginning */
> +			nextres = list_entry(dlm->purge_list.next,
> +					     struct dlm_lock_resource, purge);
> +		else if (!list_is_last(&lockres->purge,&dlm->purge_list))
> +			nextres = list_entry(lockres->purge.next,
> +					     struct dlm_lock_resource, purge);
> +		else
> +			nextres = NULL;
> +
> +		if (__dlm_lockres_unused(lockres)) {
> +			if (!list_empty(&lockres->purge)) {
> +				list_del_init(&lockres->purge);
> +				dlm->purge_count--;
> +			}
> +			__dlm_unhash_lockres(lockres);
> +			spin_unlock(&lockres->spinlock);
> +			wake_up(&lockres->wq);
> +			dlm_lockres_put(lockres);
> +		} else
> +			spin_unlock(&lockres->spinlock);
> +		lockres = nextres;
> +
> +		/* Avoid adding any scheduling latencies. If dlm spinlock is
> +		 * dropped, retry again from the beginning as purgelist could
> +		 * have been modified */
> +		if (cond_resched_lock(&dlm->spinlock))
> +			lockres = list_entry(dlm->purge_list.next,
> +					     struct dlm_lock_resource, purge);
>   	}
>
>   	spin_unlock(&dlm->spinlock);
> @@ -733,7 +734,7 @@ in_progress:
>   			/* unlikely, but we may need to give time to
>   			 * other tasks */
>   			if (!--n) {
> -				mlog(0, "throttling dlm_thread\n");
> +				mlog(0, "throttling dlm_thread n=%d\n", n);
>   				break;
>   			}
>   		}
>    

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