[Ocfs2-devel] [PATCH 5/6] ocfs2: Avoid blocking in ocfs2_mark_lockres_freeing() in downconvert thread
Jan Kara
jack at suse.cz
Fri Feb 21 01:14:15 PST 2014
On Thu 20-02-14 21:21:14, Srinivas Eeda wrote:
> 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 ?
Ah, right. Somehow I missed that. I'll send fixed version in a moment.
Honza
>
> 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 <jack at 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);
>
--
Jan Kara <jack at suse.cz>
SUSE Labs, CR
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