[PATCH 3.12 034/181] ocfs2: avoid blocking in ocfs2_mark_lockres_freeing() in downconvert thread

Jiri Slaby
2014-06-30T11:56:55Z

From: Jan Kara <jack@suse.cz>

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit 84d86f83f9d0e8431a3c9eae4c47e9d7ff49a411 upstream.

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@suse.cz>
Reviewed-by: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Srinivas Eeda <srinivas.eeda@oracle.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
fs/ocfs2/dlmglue.c | 44 +++++++++++++++++++++++++++++++++++++++++---
fs/ocfs2/dlmglue.h | 3 ++-
fs/ocfs2/inode.c | 7 ++++---
3 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 3a44a648dae7..3988d0aeb72c 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -3142,22 +3142,60 @@ out:
return 0;
}

+static void ocfs2_process_blocked_lock(struct ocfs2_super *osb,
+ struct ocfs2_lock_res *lockres);
+
/* Mark the lockres as being dropped. It will no longer be
* queued if blocking, but we still may have to wait on it
* being dequeued from the downconvert thread before we can consider
* 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;
- unsigned long flags;
+ unsigned long flags, flags2;

ocfs2_init_mask_waiter(&mw);

spin_lock_irqsave(&lockres->l_lock, flags);
lockres->l_flags |= OCFS2_LOCK_FREEING;
+ if (lockres->l_flags & OCFS2_LOCK_QUEUED && current == osb->dc_task) {
+ /*
+ * 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_unlock_irqrestore(&lockres->l_lock, flags);
+ spin_lock_irqsave(&osb->dc_task_lock, flags2);
+ list_del_init(&lockres->l_blocked_list);
+ osb->blocked_lock_count--;
+ spin_unlock_irqrestore(&osb->dc_task_lock, flags2);
+ /*
+ * Warn if we recurse into another post_unlock call. Strictly
+ * speaking it isn't a problem but we need to be careful if
+ * that happens (stack overflow, deadlocks, ...) so warn if
+ * ocfs2 grows a path for which this can happen.
+ */
+ WARN_ON_ONCE(lockres->l_ops->post_unlock);
+ /* Since the lock is freeing we don't do much in the fn below */
+ ocfs2_process_blocked_lock(osb, lockres);
+ return;
+ }
while (lockres->l_flags & OCFS2_LOCK_QUEUED) {
lockres_add_mask_waiter(lockres, &mw, OCFS2_LOCK_QUEUED, 0);
spin_unlock_irqrestore(&lockres->l_lock, flags);
@@ -3178,7 +3216,7 @@ 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 059fa362f4c0..e37a59a28644 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1069,6 +1069,7 @@ 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,
@@ -1085,9 +1086,9 @@ 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);
--
2.0.0