[PATCH 3/4] fs: add fput_queue

[Jeff Layton <jlayton@poochiereds.net>]

Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
---
 fs/file_table.c      | 18 ++++++++++++++++++
 include/linux/file.h |  1 +
 2 files changed, 19 insertions(+)

diff --git a/fs/file_table.c b/fs/file_table.c
index d63f4a399d39..1ad2e3fd2064 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -297,6 +297,24 @@ void fput(struct file *file)
 }
 EXPORT_SYMBOL(fput);
 
+/**
+ * fput_queue - do an fput without using task_work
+ * @file: file of which to put the reference
+ *
+ * If we need to ensure that the final __fput is done on a file before
+ * returning to userland, then we can't queue it to task_work. For that we
+ * borrow the infrastructure used by kthreads, and the task can then just
+ * called flush_delayed_fput to ensure that the final fput has completed.
+ */
+void fput_queue(struct file *file)
+{
+	if (atomic_long_dec_and_test(&file->f_count)) {
+		if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
+			schedule_delayed_work(&delayed_fput_work, 1);
+	}
+}
+EXPORT_SYMBOL(fput_queue);
+
 /*
  * synchronous analog of fput(); for kernel threads that might be needed
  * in some umount() (and thus can't use flush_delayed_fput() without
diff --git a/include/linux/file.h b/include/linux/file.h
index f87d30882a24..543b0e2faf2c 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -12,6 +12,7 @@
 struct file;
 
 extern void fput(struct file *);
+extern void fput_queue(struct file *);
 
 struct file_operations;
 struct vfsmount;
-- 
2.4.3