I like the idea of dc_task handling queued basts in
ocfs2_mark_lockres_freeing.
I am wondering if we should call lockres->l_ops->post_unlock(osb,
lockres) ? Would there be another node waiting for a bast response ?
On 02/20/2014 07:18 AM, Jan Kara wrote:
> If we are dropping last inode reference from downconvert thread, we will
> end up calling ocfs2_mark_lockres_freeing() which can block if the lock
> we are freeing is queued thus creating an A-A deadlock. Luckily, since
> we are the downconvert thread, we can immediately dequeue the lock and
> thus avoid waiting in this case.
>
> Signed-off-by: Jan Kara <j...@suse.cz>
> ---
> fs/ocfs2/dlmglue.c | 33 +++++++++++++++++++++++++++++++--
> fs/ocfs2/dlmglue.h | 3 ++-
> fs/ocfs2/inode.c | 7 ++++---
> 3 files changed, 37 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index 19986959d149..b7580157ef01 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -3150,7 +3150,8 @@ out:
> * it safe to drop.
> *
> * You can *not* attempt to call cluster_lock on this lockres anymore. */
> -void ocfs2_mark_lockres_freeing(struct ocfs2_lock_res *lockres)
> +void ocfs2_mark_lockres_freeing(struct ocfs2_super *osb,
> + struct ocfs2_lock_res *lockres)
> {
> int status;
> struct ocfs2_mask_waiter mw;
> @@ -3160,6 +3161,33 @@ void ocfs2_mark_lockres_freeing(struct ocfs2_lock_res
> *lockres)
>
> spin_lock_irqsave(&lockres->l_lock, flags);
> lockres->l_flags |= OCFS2_LOCK_FREEING;
> + if (lockres->l_flags & OCFS2_LOCK_QUEUED && current == osb->dc_task) {
> + unsigned long flags;
> +
> + /*
> + * We know the downconvert is queued but not in progress
> + * because we are the downconvert thread and processing
> + * different lock. So we can just remove the lock from the
> + * queue. This is not only an optimization but also a way
> + * to avoid the following deadlock:
> + * ocfs2_dentry_post_unlock()
> + * ocfs2_dentry_lock_put()
> + * ocfs2_drop_dentry_lock()
> + * iput()
> + * ocfs2_evict_inode()
> + * ocfs2_clear_inode()
> + * ocfs2_mark_lockres_freeing()
> + * ... blocks waiting for OCFS2_LOCK_QUEUED
> + * since we are the downconvert thread which
> + * should clear the flag.
> + */
> + spin_lock_irqsave(&osb->dc_task_lock, flags);
> + list_del_init(&lockres->l_blocked_list);
> + osb->blocked_lock_count--;
> + spin_unlock_irqrestore(&osb->dc_task_lock, flags);
> + lockres_clear_flags(lockres, OCFS2_LOCK_QUEUED);
> + goto out_unlock;
> + }
> while (lockres->l_flags & OCFS2_LOCK_QUEUED) {
> lockres_add_mask_waiter(lockres, &mw, OCFS2_LOCK_QUEUED, 0);
> spin_unlock_irqrestore(&lockres->l_lock, flags);
> @@ -3172,6 +3200,7 @@ void ocfs2_mark_lockres_freeing(struct ocfs2_lock_res
> *lockres)
>
> spin_lock_irqsave(&lockres->l_lock, flags);
> }
> +out_unlock:
> spin_unlock_irqrestore(&lockres->l_lock, flags);
> }
>
> @@ -3180,7 +3209,7 @@ void ocfs2_simple_drop_lockres(struct ocfs2_super *osb,
> {
> int ret;
>
> - ocfs2_mark_lockres_freeing(lockres);
> + ocfs2_mark_lockres_freeing(osb, lockres);
> ret = ocfs2_drop_lock(osb, lockres);
> if (ret)
> mlog_errno(ret);
> diff --git a/fs/ocfs2/dlmglue.h b/fs/ocfs2/dlmglue.h
> index 1d596d8c4a4a..d293a22c32c5 100644
> --- a/fs/ocfs2/dlmglue.h
> +++ b/fs/ocfs2/dlmglue.h
> @@ -157,7 +157,8 @@ int ocfs2_refcount_lock(struct ocfs2_refcount_tree
> *ref_tree, int ex);
> void ocfs2_refcount_unlock(struct ocfs2_refcount_tree *ref_tree, int ex);
>
>
> -void ocfs2_mark_lockres_freeing(struct ocfs2_lock_res *lockres);
> +void ocfs2_mark_lockres_freeing(struct ocfs2_super *osb,
> + struct ocfs2_lock_res *lockres);
> void ocfs2_simple_drop_lockres(struct ocfs2_super *osb,
> struct ocfs2_lock_res *lockres);
>
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index 3b0d722de35e..9661f8db21dc 100644
> --- a/fs/ocfs2/inode.c
> +++ b/fs/ocfs2/inode.c
> @@ -1053,6 +1053,7 @@ static void ocfs2_clear_inode(struct inode *inode)
> {
> int status;
> struct ocfs2_inode_info *oi = OCFS2_I(inode);
> + struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
>
> clear_inode(inode);
> trace_ocfs2_clear_inode((unsigned long long)oi->ip_blkno,
> @@ -1069,9 +1070,9 @@ static void ocfs2_clear_inode(struct inode *inode)
>
> /* Do these before all the other work so that we don't bounce
> * the downconvert thread while waiting to destroy the locks. */
> - ocfs2_mark_lockres_freeing(&oi->ip_rw_lockres);
> - ocfs2_mark_lockres_freeing(&oi->ip_inode_lockres);
> - ocfs2_mark_lockres_freeing(&oi->ip_open_lockres);
> + ocfs2_mark_lockres_freeing(osb, &oi->ip_rw_lockres);
> + ocfs2_mark_lockres_freeing(osb, &oi->ip_inode_lockres);
> + ocfs2_mark_lockres_freeing(osb, &oi->ip_open_lockres);
>
> ocfs2_resv_discard(&OCFS2_SB(inode->i_sb)->osb_la_resmap,
> &oi->ip_la_data_resv);
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