[Ocfs2-devel] [PATCH] ocfs2/dlm: remove a potential deadlock

[Wengang Wang]

I am taking back this patch since where is another such violation in
dlm_flush_asts().

I will try to fix the both in one combination.

regards,
wengang.

On 10-09-02 21:17, Wengang Wang wrote:
> /*
>  *
>  * spinlock lock ordering: if multiple locks are needed, obey this ordering:
>  *    dlm_domain_lock
>  *    struct dlm_ctxt->spinlock
>  *    struct dlm_lock_resource->spinlock
>  *    struct dlm_ctxt->master_lock
>  *    struct dlm_ctxt->ast_lock
>  *    dlm_master_list_entry->spinlock
>  *    dlm_lock->spinlock
>  *
>  */
> 
> There is a violation that locks on dlm_lock_resource->spinlock after locking
> on dlm_ctxt->ast_lock. The violation is not detected because so far there is
> only one place where both the two spinlock are taken at the same time. But it
> is a potential deadlock in future(when the two lock are taken all together in
> correct order).
> 
> This patch fixes the problem by changing the calling order.
> 
> Signed-off-by: Wengang Wang <wen.gang.wang at oracle.com>
> ---
>  fs/ocfs2/dlm/dlmthread.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ocfs2/dlm/dlmthread.c b/fs/ocfs2/dlm/dlmthread.c
> index 2211acf..676ff3e 100644
> --- a/fs/ocfs2/dlm/dlmthread.c
> +++ b/fs/ocfs2/dlm/dlmthread.c
> @@ -671,8 +671,8 @@ static int dlm_thread(void *data)
>  		 	/* lockres can be re-dirtied/re-added to the
>  			 * dirty_list in this gap, but that is ok */
>  
> -			spin_lock(&dlm->ast_lock);
>  			spin_lock(&res->spinlock);
> +			spin_lock(&dlm->ast_lock);
>  			if (res->owner != dlm->node_num) {
>  				__dlm_print_one_lock_resource(res);
>  				mlog(ML_ERROR, "inprog:%s, mig:%s, reco:%s, dirty:%s\n",
> @@ -691,8 +691,8 @@ static int dlm_thread(void *data)
>  					  DLM_LOCK_RES_RECOVERING)) {
>  				/* move it to the tail and keep going */
>  				res->state &= ~DLM_LOCK_RES_DIRTY;
> -				spin_unlock(&res->spinlock);
>  				spin_unlock(&dlm->ast_lock);
> +				spin_unlock(&res->spinlock);
>  				mlog(0, "delaying list shuffling for in-"
>  				     "progress lockres %.*s, state=%d\n",
>  				     res->lockname.len, res->lockname.name,
> @@ -713,8 +713,8 @@ static int dlm_thread(void *data)
>  			/* called while holding lockres lock */
>  			dlm_shuffle_lists(dlm, res);
>  			res->state &= ~DLM_LOCK_RES_DIRTY;
> -			spin_unlock(&res->spinlock);
>  			spin_unlock(&dlm->ast_lock);
> +			spin_unlock(&res->spinlock);
>  
>  			dlm_lockres_calc_usage(dlm, res);
>  
> -- 
> 1.7.2.2
> 
> 
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