[Ocfs2-devel] [PATCH 4/6] ocfs2: Implement delayed dropping of last dquot reference
Srinivas Eeda
srinivas.eeda at oracle.com
Thu Feb 20 21:15:12 PST 2014
looks good to me
Reviewed-by: Srinivas Eeda <srinivas.eeda at 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 at 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);
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