kernfs: Skip kernfs_drain_open_files() more aggressively

Track the number of mmapped files and files that need to be released and
skip kernfs_drain_open_file() if both are zero, which are the precise
conditions which require draining open_files. The early exit test is
factored into kernfs_should_drain_open_files() which is now tested by
kernfs_drain_open_files()'s caller - kernfs_drain().

This isn't a meaningful optimization on its own but will enable future
stand-alone kernfs_deactivate() implementation.

v2: Chengming noticed that on->nr_to_release was leaking after ->open()
    failure. Fix it by telling kernfs_unlink_open_file() that it's called
    from the ->open() fail path and should dec the counter. Use kzalloc() to
    allocate kernfs_open_node so that the tracking fields are correctly
    initialized.

Cc: Chengming Zhou <[email protected]>
Tested-by: Chengming Zhou <[email protected]>
Reviewed-by: Chengming Zhou <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 3ae214d02d44..fc5821effd97 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -157,6 +157,7 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
  */
 extern const struct file_operations kernfs_file_fops;
 
+bool kernfs_should_drain_open_files(struct kernfs_node *kn);
 void kernfs_drain_open_files(struct kernfs_node *kn);
 
 /*