ocfs2: implement delayed dropping of last dquot reference
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>
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>
diff --git a/fs/ocfs2/quota_global.c b/fs/ocfs2/quota_global.c
index d7b5108..b990a62 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 @@
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 @@
/* 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;