Fix kernel oops when CONFIG_DEBUG_ATOMIC_SLEEP is enabled.

Removed oplock_break_received flag which was added to achieve
synchronization between oplock handler and open handler by earlier commit.

It is not needed because there is an existing lock open_file_lock to achieve
the same. find_readable_file takes open_file_lock and then traverses the
openFileList. Similarly, cifs_oplock_break while closing the deferred
handle (i.e cifsFileInfo_put) takes open_file_lock and then sends close
to the server.

Added comments for better readability.

Signed-off-by: Rohith Surabattula <rohiths@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: rohiths-msft

fs/cifs/cifsfs.c

@@ -133,7 +133,7 @@ struct workqueue_struct	*cifsiod_wq;
 struct workqueue_struct	*decrypt_wq;
 struct workqueue_struct	*fileinfo_put_wq;
 struct workqueue_struct	*cifsoplockd_wq;
-struct workqueue_struct *deferredclose_wq;
+struct workqueue_struct	*deferredclose_wq;
 __u32 cifs_lock_secret;
 
 /*

fs/cifs/cifsglob.h

@@ -1257,8 +1257,7 @@ struct cifsFileInfo {
 	struct work_struct oplock_break; /* work for oplock breaks */
 	struct work_struct put; /* work for the final part of _put */
 	struct delayed_work deferred;
-	bool oplock_break_received; /* Flag to indicate oplock break */
-	bool deferred_scheduled;
+	bool deferred_close_scheduled; /* Flag to indicate close is scheduled */
 };
 
 struct cifs_io_parms {

fs/cifs/file.c

@@ -323,8 +323,7 @@ cifs_new_fileinfo(struct cifs_fid *fid, struct file *file,
 	cfile->dentry = dget(dentry);
 	cfile->f_flags = file->f_flags;
 	cfile->invalidHandle = false;
-	cfile->oplock_break_received = false;
-	cfile->deferred_scheduled = false;
+	cfile->deferred_close_scheduled = false;
 	cfile->tlink = cifs_get_tlink(tlink);
 	INIT_WORK(&cfile->oplock_break, cifs_oplock_break);
 	INIT_WORK(&cfile->put, cifsFileInfo_put_work);
@@ -574,21 +573,18 @@ int cifs_open(struct inode *inode, struct file *file)
 			file->f_op = &cifs_file_direct_ops;
 	}
 
-	spin_lock(&CIFS_I(inode)->deferred_lock);
 	/* Get the cached handle as SMB2 close is deferred */
 	rc = cifs_get_readable_path(tcon, full_path, &cfile);
 	if (rc == 0) {
 		if (file->f_flags == cfile->f_flags) {
 			file->private_data = cfile;
+			spin_lock(&CIFS_I(inode)->deferred_lock);
 			cifs_del_deferred_close(cfile);
 			spin_unlock(&CIFS_I(inode)->deferred_lock);
 			goto out;
 		} else {
-			spin_unlock(&CIFS_I(inode)->deferred_lock);
 			_cifsFileInfo_put(cfile, true, false);
 		}
-	} else {
-		spin_unlock(&CIFS_I(inode)->deferred_lock);
 	}
 
 	if (server->oplocks)
@@ -878,12 +874,12 @@ void smb2_deferred_work_close(struct work_struct *work)
 			struct cifsFileInfo, deferred.work);
 
 	spin_lock(&CIFS_I(d_inode(cfile->dentry))->deferred_lock);
-	if (!cfile->deferred_scheduled) {
+	if (!cfile->deferred_close_scheduled) {
 		spin_unlock(&CIFS_I(d_inode(cfile->dentry))->deferred_lock);
 		return;
 	}
 	cifs_del_deferred_close(cfile);
-	cfile->deferred_scheduled = false;
+	cfile->deferred_close_scheduled = false;
 	spin_unlock(&CIFS_I(d_inode(cfile->dentry))->deferred_lock);
 	_cifsFileInfo_put(cfile, true, false);
 }
@@ -905,14 +901,15 @@ int cifs_close(struct inode *inode, struct file *file)
 				inode->i_ctime = inode->i_mtime = current_time(inode);
 			spin_lock(&cinode->deferred_lock);
 			cifs_add_deferred_close(cfile, dclose);
-			if (cfile->deferred_scheduled) {
+			if (cfile->deferred_close_scheduled &&
+			    delayed_work_pending(&cfile->deferred)) {
 				mod_delayed_work(deferredclose_wq,
 						&cfile->deferred, cifs_sb->ctx->acregmax);
 			} else {
 				/* Deferred close for files */
 				queue_delayed_work(deferredclose_wq,
 						&cfile->deferred, cifs_sb->ctx->acregmax);
-				cfile->deferred_scheduled = true;
+				cfile->deferred_close_scheduled = true;
 				spin_unlock(&cinode->deferred_lock);
 				return 0;
 			}
@@ -2020,8 +2017,7 @@ struct cifsFileInfo *find_readable_file(struct cifsInodeInfo *cifs_inode,
 		if (fsuid_only && !uid_eq(open_file->uid, current_fsuid()))
 			continue;
 		if (OPEN_FMODE(open_file->f_flags) & FMODE_READ) {
-			if ((!open_file->invalidHandle) &&
-				(!open_file->oplock_break_received)) {
+			if ((!open_file->invalidHandle)) {
 				/* found a good file */
 				/* lock it so it will not be closed on us */
 				cifsFileInfo_get(open_file);
@@ -4874,13 +4870,14 @@ void cifs_oplock_break(struct work_struct *work)
 	}
 	/*
 	 * When oplock break is received and there are no active
-	 * file handles but cached, then set the flag oplock_break_received.
+	 * file handles but cached, then schedule deferred close immediately.
 	 * So, new open will not use cached handle.
 	 */
 	spin_lock(&CIFS_I(inode)->deferred_lock);
 	is_deferred = cifs_is_deferred_close(cfile, &dclose);
-	if (is_deferred && cfile->deferred_scheduled) {
-		cfile->oplock_break_received = true;
+	if (is_deferred &&
+	    cfile->deferred_close_scheduled &&
+	    delayed_work_pending(&cfile->deferred)) {
 		mod_delayed_work(deferredclose_wq, &cfile->deferred, 0);
 	}
 	spin_unlock(&CIFS_I(inode)->deferred_lock);

fs/cifs/misc.c

@@ -672,6 +672,9 @@ cifs_add_pending_open(struct cifs_fid *fid, struct tcon_link *tlink,
 	spin_unlock(&tlink_tcon(open->tlink)->open_file_lock);
 }
 
+/*
+ * Critical section which runs after acquiring deferred_lock.
+ */
 bool
 cifs_is_deferred_close(struct cifsFileInfo *cfile, struct cifs_deferred_close **pdclose)
 {
@@ -688,6 +691,9 @@ cifs_is_deferred_close(struct cifsFileInfo *cfile, struct cifs_deferred_close **
 	return false;
 }
 
+/*
+ * Critical section which runs after acquiring deferred_lock.
+ */
 void
 cifs_add_deferred_close(struct cifsFileInfo *cfile, struct cifs_deferred_close *dclose)
 {
@@ -707,6 +713,9 @@ cifs_add_deferred_close(struct cifsFileInfo *cfile, struct cifs_deferred_close *
 	list_add_tail(&dclose->dlist, &CIFS_I(d_inode(cfile->dentry))->deferred_closes);
 }
 
+/*
+ * Critical section which runs after acquiring deferred_lock.
+ */
 void
 cifs_del_deferred_close(struct cifsFileInfo *cfile)
 {