fput: turn "list_head delayed_fput_list" into llist_head

commit 4f5e65a1cc90bbb15b9f6cdc362922af1bcc155a upstream.

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>
Signed-off-by: Wang Kai <morgan.wang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/file_table.c b/fs/file_table.c
index 54a34be444f904353a6cf2d2a669ccc0c559bd4f..cd4ef34bb641fab78f62c4a2874960e151a4c352 100644 (file)
--- 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))) {
@@ -314,10 +310,9 @@ void fput(struct file *file)
                        if (!task_work_add(task, &file->f_u.fu_rcuhead, true))
                                return;
                }
-               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 b01f3fb5ea0adf4ac860c0830f5c79b7636e10e6..9c44db035d2e3b5f786431ab246635ca6910eb80 100644 (file)
--- 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>
@@ -806,6 +807,7 @@ struct file {
         */
        union {
                struct list_head        fu_list;
+               struct llist_node       fu_llist;
                struct rcu_head         fu_rcuhead;
        } f_u;
        struct path             f_path;