[Ocfs2-devel] [PATCH 4/6] ocfs2: Implement delayed dropping of last dquot reference

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

looks good to me
Reviewed-by: Srinivas Eeda <srinivas.eeda@oracle.com>

On 02/20/2014 07:18 AM, Jan Kara wrote:
> We cannot drop last dquot reference from downconvert thread as that
> creates the following deadlock:
>
> NODE 1                                  NODE2
> holds dentry lock for 'foo'
> holds inode lock for GLOBAL_BITMAP_SYSTEM_INODE
>                                          dquot_initialize(bar)
>                                            ocfs2_dquot_acquire()
>                                              ocfs2_inode_lock(USER_QUOTA_SYSTEM_INODE)
>                                              ...
> downconvert thread (triggered from another
> node or a different process from NODE2)
>    ocfs2_dentry_post_unlock()
>      ...
>      iput(foo)
>        ocfs2_evict_inode(foo)
>          ocfs2_clear_inode(foo)
>            dquot_drop(inode)
>              ...
> 	    ocfs2_dquot_release()
>                ocfs2_inode_lock(USER_QUOTA_SYSTEM_INODE)
>                 - blocks
>                                              finds we need more space in
>                                              quota file
>                                              ...
>                                              ocfs2_extend_no_holes()
>                                                ocfs2_inode_lock(GLOBAL_BITMAP_SYSTEM_INODE)
>                                                  - deadlocks waiting for
>                                                    downconvert thread
>
> We solve the problem by postponing dropping of the last dquot reference
> to a workqueue if it happens from the downconvert thread.
>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>   fs/ocfs2/ocfs2.h        |  5 +++++
>   fs/ocfs2/quota.h        |  2 ++
>   fs/ocfs2/quota_global.c | 35 +++++++++++++++++++++++++++++++++++
>   fs/ocfs2/super.c        |  8 ++++++++
>   4 files changed, 50 insertions(+)
>
> diff --git a/fs/ocfs2/ocfs2.h b/fs/ocfs2/ocfs2.h
> index 553f53cc73ae..64c02239ba46 100644
> --- a/fs/ocfs2/ocfs2.h
> +++ b/fs/ocfs2/ocfs2.h
> @@ -30,6 +30,7 @@
>   #include <linux/sched.h>
>   #include <linux/wait.h>
>   #include <linux/list.h>
> +#include <linux/llist.h>
>   #include <linux/rbtree.h>
>   #include <linux/workqueue.h>
>   #include <linux/kref.h>
> @@ -419,6 +420,10 @@ struct ocfs2_super
>   	struct ocfs2_dentry_lock *dentry_lock_list;
>   	struct work_struct dentry_lock_work;
>   
> +	/* List of dquot structures to drop last reference to */
> +	struct llist_head dquot_drop_list;
> +	struct work_struct dquot_drop_work;
> +
>   	wait_queue_head_t		osb_mount_event;
>   
>   	/* Truncate log info */
> diff --git a/fs/ocfs2/quota.h b/fs/ocfs2/quota.h
> index d5ab56cbe5c5..f266d67df3c6 100644
> --- a/fs/ocfs2/quota.h
> +++ b/fs/ocfs2/quota.h
> @@ -28,6 +28,7 @@ struct ocfs2_dquot {
>   	unsigned int dq_use_count;	/* Number of nodes having reference to this entry in global quota file */
>   	s64 dq_origspace;	/* Last globally synced space usage */
>   	s64 dq_originodes;	/* Last globally synced inode usage */
> +	struct llist_node list;	/* Member of list of dquots to drop */
>   };
>   
>   /* Description of one chunk to recover in memory */
> @@ -110,6 +111,7 @@ int ocfs2_read_quota_phys_block(struct inode *inode, u64 p_block,
>   int ocfs2_create_local_dquot(struct dquot *dquot);
>   int ocfs2_local_release_dquot(handle_t *handle, struct dquot *dquot);
>   int ocfs2_local_write_dquot(struct dquot *dquot);
> +void ocfs2_drop_dquot_refs(struct work_struct *work);
>   
>   extern const struct dquot_operations ocfs2_quota_operations;
>   extern struct quota_format_type ocfs2_quota_format;
> diff --git a/fs/ocfs2/quota_global.c b/fs/ocfs2/quota_global.c
> index aaa50611ec66..7921e209c64b 100644
> --- a/fs/ocfs2/quota_global.c
> +++ b/fs/ocfs2/quota_global.c
> @@ -10,6 +10,7 @@
>   #include <linux/jiffies.h>
>   #include <linux/writeback.h>
>   #include <linux/workqueue.h>
> +#include <linux/llist.h>
>   
>   #include <cluster/masklog.h>
>   
> @@ -679,6 +680,27 @@ static int ocfs2_calc_qdel_credits(struct super_block *sb, int type)
>   	       OCFS2_INODE_UPDATE_CREDITS;
>   }
>   
> +void ocfs2_drop_dquot_refs(struct work_struct *work)
> +{
> +	struct ocfs2_super *osb = container_of(work, struct ocfs2_super,
> +					       dquot_drop_work);
> +	struct llist_node *list;
> +	struct ocfs2_dquot *odquot, *next_odquot;
> +
> +	list = llist_del_all(&osb->dquot_drop_list);
> +	llist_for_each_entry_safe(odquot, next_odquot, list, list) {
> +		/* Drop the reference we acquired in ocfs2_dquot_release() */
> +		dqput(&odquot->dq_dquot);
> +	}
> +}
> +
> +/*
> + * Called when the last reference to dquot is dropped. If we are called from
> + * downconvert thread, we cannot do all the handling here because grabbing
> + * quota lock could deadlock (the node holding the quota lock could need some
> + * other cluster lock to proceed but with blocked downconvert thread we cannot
> + * release any lock).
> + */
>   static int ocfs2_release_dquot(struct dquot *dquot)
>   {
>   	handle_t *handle;
> @@ -694,6 +716,19 @@ static int ocfs2_release_dquot(struct dquot *dquot)
>   	/* Check whether we are not racing with some other dqget() */
>   	if (atomic_read(&dquot->dq_count) > 1)
>   		goto out;
> +	/* Running from downconvert thread? Postpone quota processing to wq */
> +	if (current == osb->dc_task) {
> +		/*
> +		 * Grab our own reference to dquot and queue it for delayed
> +		 * dropping.  Quota code rechecks after calling
> +		 * ->release_dquot() and won't free dquot structure.
> +		 */
> +		dqgrab(dquot);
> +		/* First entry on list -> queue work */
> +		if (llist_add(&OCFS2_DQUOT(dquot)->list, &osb->dquot_drop_list))
> +			queue_work(ocfs2_wq, &osb->dquot_drop_work);
> +		goto out;
> +	}
>   	status = ocfs2_lock_global_qf(oinfo, 1);
>   	if (status < 0)
>   		goto out;
> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> index 49d84f80f36c..0a8972deae2b 100644
> --- a/fs/ocfs2/super.c
> +++ b/fs/ocfs2/super.c
> @@ -1943,6 +1943,11 @@ static void ocfs2_dismount_volume(struct super_block *sb, int mnt_err)
>   
>   	ocfs2_disable_quotas(osb);
>   
> +	/* All dquots should be freed by now */
> +	WARN_ON(!llist_empty(&osb->dquot_drop_list));
> +	/* Wait for worker to be done with the work structure in osb */
> +	cancel_work_sync(&osb->dquot_drop_work);
> +
>   	ocfs2_shutdown_local_alloc(osb);
>   
>   	/* This will disable recovery and flush any recovery work. */
> @@ -2279,6 +2284,9 @@ static int ocfs2_initialize_super(struct super_block *sb,
>   	INIT_WORK(&osb->dentry_lock_work, ocfs2_drop_dl_inodes);
>   	osb->dentry_lock_list = NULL;
>   
> +	INIT_WORK(&osb->dquot_drop_work, ocfs2_drop_dquot_refs);
> +	init_llist_head(&osb->dquot_drop_list);
> +
>   	/* get some pseudo constants for clustersize bits */
>   	osb->s_clustersize_bits =
>   		le32_to_cpu(di->id2.i_super.s_clustersize_bits);