cifs: convert oplock breaks to use slow_work facility (try #4)

This is the fourth respin of the patch to convert oplock breaks to
use the slow_work facility.

A customer of ours was testing a backport of one of the earlier
patchsets, and hit a "Busy inodes after umount..." problem. An oplock
break job had raced with a umount, and the superblock got torn down and
its memory reused. When the oplock break job tried to dereference the
inode->i_sb, the kernel oopsed.

This patchset has the oplock break job hold an inode and vfsmount
reference until the oplock break completes.  With this, there should be
no need to take a tcon reference (the vfsmount implicitly holds one
already).

Currently, when an oplock break comes in there's a chance that the
oplock break job won't occur if the allocation of the oplock_q_entry
fails. There are also some rather nasty races in the allocation and
handling these structs.

Rather than allocating oplock queue entries when an oplock break comes
in, add a few extra fields to the cifsFileInfo struct. Get rid of the
dedicated cifs_oplock_thread as well and queue the oplock break job to
the slow_work thread pool.

This approach also has the advantage that the oplock break jobs can
potentially run in parallel rather than be serialized like they are
today.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 5 insertions, 90 deletions

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 3610e9958b4c..89142b39fec1 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -64,9 +64,6 @@ unsigned int multiuser_mount = 0;
 unsigned int extended_security = CIFSSEC_DEF;
 /* unsigned int ntlmv2_support = 0; */
 unsigned int sign_CIFS_PDUs = 1;
-extern struct task_struct *oplockThread; /* remove sparse warning */
-struct task_struct *oplockThread = NULL;
-/* extern struct task_struct * dnotifyThread; remove sparse warning */
 static const struct super_operations cifs_super_ops;
 unsigned int CIFSMaxBufSize = CIFS_MAX_MSGSIZE;
 module_param(CIFSMaxBufSize, int, 0);
@@ -973,89 +970,12 @@ cifs_destroy_mids(void)
 	kmem_cache_destroy(cifs_oplock_cachep);
 }
 
-static int cifs_oplock_thread(void *dummyarg)
-{
-	struct oplock_q_entry *oplock_item;
-	struct cifsTconInfo *pTcon;
-	struct inode *inode;
-	__u16  netfid;
-	int rc, waitrc = 0;
-
-	set_freezable();
-	do {
-		if (try_to_freeze())
-			continue;
-
-		spin_lock(&cifs_oplock_lock);
-		if (list_empty(&cifs_oplock_list)) {
-			spin_unlock(&cifs_oplock_lock);
-			set_current_state(TASK_INTERRUPTIBLE);
-			schedule_timeout(39*HZ);
-		} else {
-			oplock_item = list_entry(cifs_oplock_list.next,
-						struct oplock_q_entry, qhead);
-			cFYI(1, ("found oplock item to write out"));
-			pTcon = oplock_item->tcon;
-			inode = oplock_item->pinode;
-			netfid = oplock_item->netfid;
-			spin_unlock(&cifs_oplock_lock);
-			DeleteOplockQEntry(oplock_item);
-			/* can not grab inode sem here since it would
-				deadlock when oplock received on delete
-				since vfs_unlink holds the i_mutex across
-				the call */
-			/* mutex_lock(&inode->i_mutex);*/
-			if (S_ISREG(inode->i_mode)) {
-#ifdef CONFIG_CIFS_EXPERIMENTAL
-				if (CIFS_I(inode)->clientCanCacheAll == 0)
-					break_lease(inode, FMODE_READ);
-				else if (CIFS_I(inode)->clientCanCacheRead == 0)
-					break_lease(inode, FMODE_WRITE);
-#endif
-				rc = filemap_fdatawrite(inode->i_mapping);
-				if (CIFS_I(inode)->clientCanCacheRead == 0) {
-					waitrc = filemap_fdatawait(
-							      inode->i_mapping);
-					invalidate_remote_inode(inode);
-				}
-				if (rc == 0)
-					rc = waitrc;
-			} else
-				rc = 0;
-			/* mutex_unlock(&inode->i_mutex);*/
-			if (rc)
-				CIFS_I(inode)->write_behind_rc = rc;
-			cFYI(1, ("Oplock flush inode %p rc %d",
-				inode, rc));
-
-				/* releasing stale oplock after recent reconnect
-				of smb session using a now incorrect file
-				handle is not a data integrity issue but do
-				not bother sending an oplock release if session
-				to server still is disconnected since oplock
-				already released by the server in that case */
-			if (!pTcon->need_reconnect) {
-				rc = CIFSSMBLock(0, pTcon, netfid,
-						0 /* len */ , 0 /* offset */, 0,
-						0, LOCKING_ANDX_OPLOCK_RELEASE,
-						false /* wait flag */);
-				cFYI(1, ("Oplock release rc = %d", rc));
-			}
-			set_current_state(TASK_INTERRUPTIBLE);
-			schedule_timeout(1);  /* yield in case q were corrupt */
-		}
-	} while (!kthread_should_stop());
-
-	return 0;
-}
-
 static int __init
 init_cifs(void)
 {
 	int rc = 0;
 	cifs_proc_init();
 	INIT_LIST_HEAD(&cifs_tcp_ses_list);
-	INIT_LIST_HEAD(&cifs_oplock_list);
 #ifdef CONFIG_CIFS_EXPERIMENTAL
 	INIT_LIST_HEAD(&GlobalDnotifyReqList);
 	INIT_LIST_HEAD(&GlobalDnotifyRsp_Q);
@@ -1084,7 +1004,6 @@ init_cifs(void)
 	rwlock_init(&GlobalSMBSeslock);
 	rwlock_init(&cifs_tcp_ses_lock);
 	spin_lock_init(&GlobalMid_Lock);
-	spin_lock_init(&cifs_oplock_lock);
 
 	if (cifs_max_pending < 2) {
 		cifs_max_pending = 2;
@@ -1119,18 +1038,15 @@ init_cifs(void)
 	if (rc)
 		goto out_unregister_key_type;
 #endif
-	oplockThread = kthread_run(cifs_oplock_thread, NULL, "cifsoplockd");
-	if (IS_ERR(oplockThread)) {
-		rc = PTR_ERR(oplockThread);
-		cERROR(1, ("error %d create oplock thread", rc));
-		goto out_unregister_dfs_key_type;
-	}
+	rc = slow_work_register_user();
+	if (rc)
+		goto out_unregister_resolver_key;
 
 	return 0;
 
- out_unregister_dfs_key_type:
-#ifdef CONFIG_CIFS_DFS_UPCALL
+ out_unregister_resolver_key:
 	unregister_key_type(&key_type_dns_resolver);
+#ifdef CONFIG_CIFS_DFS_UPCALL
  out_unregister_key_type:
 #endif
 #ifdef CONFIG_CIFS_UPCALL
@@ -1165,7 +1081,6 @@ exit_cifs(void)
 	cifs_destroy_inodecache();
 	cifs_destroy_mids();
 	cifs_destroy_request_bufs();
-	kthread_stop(oplockThread);
 }
 
 MODULE_AUTHOR("Steve French <sfrench@us.ibm.com>");