fput: turn "list_head delayed_fput_list" into llist_head

fput() and delayed_fput() can use llist and avoid the locking.

This is unlikely path, it is not that this change can improve
the performance, but this way the code looks simpler.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrey Vagin <avagin@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

2 files changed, 12 insertions, 15 deletions

diff --git a/fs/file_table.c b/fs/file_table.c
index b9a77ad08b4d..b44e4c559786 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -265,18 +265,15 @@ static void __fput(struct file *file)
         mntput(mnt);
 }
 
-static DEFINE_SPINLOCK(delayed_fput_lock);
-static LIST_HEAD(delayed_fput_list);
+static LLIST_HEAD(delayed_fput_list);
 static void delayed_fput(struct work_struct *unused)
 {
-        LIST_HEAD(head);
-        spin_lock_irq(&delayed_fput_lock);
-        list_splice_init(&delayed_fput_list, &head);
-        spin_unlock_irq(&delayed_fput_lock);
-        while (!list_empty(&head)) {
-                struct file *f = list_first_entry(&head, struct file, f_u.fu_list);
-                list_del_init(&f->f_u.fu_list);
-                __fput(f);
+        struct llist_node *node = llist_del_all(&delayed_fput_list);
+        struct llist_node *next;
+
+        for (; node; node = next) {
+                next = llist_next(node);
+                __fput(llist_entry(node, struct file, f_u.fu_llist));
         }
 }
 
@@ -306,7 +303,6 @@ void fput(struct file *file)
 {
         if (atomic_long_dec_and_test(&file->f_count)) {
                 struct task_struct *task = current;
-                unsigned long flags;
 
                 file_sb_list_del(file);
                 if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
@@ -320,10 +316,9 @@ void fput(struct file *file)
                          * fput to avoid leaking *file.
                          */
                 }
-                spin_lock_irqsave(&delayed_fput_lock, flags);
-                list_add(&file->f_u.fu_list, &delayed_fput_list);
-                schedule_work(&delayed_fput_work);
-                spin_unlock_irqrestore(&delayed_fput_lock, flags);
+
+                if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
+                        schedule_work(&delayed_fput_work);
         }
 }
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 834c9e5113d9..d40e8e78bbd1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -10,6 +10,7 @@
 #include <linux/stat.h>
 #include <linux/cache.h>
 #include <linux/list.h>
+#include <linux/llist.h>
 #include <linux/radix-tree.h>
 #include <linux/rbtree.h>
 #include <linux/init.h>
@@ -768,6 +769,7 @@ struct file {
          */
         union {
                 struct list_head        fu_list;
+                struct llist_node       fu_llist;
                 struct rcu_head         fu_rcuhead;
         } f_u;
         struct path             f_path;