1 files changed, 71 insertions, 10 deletions

diff --git a/fs/file_table.c b/fs/file_table.c
index a305d9e2d1b2..b3fc4d67a26b 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -23,6 +23,8 @@
 #include <linux/lglock.h>
 #include <linux/percpu_counter.h>
 #include <linux/percpu.h>
+#include <linux/hardirq.h>
+#include <linux/task_work.h>
 #include <linux/ima.h>
 
 #include <linux/atomic.h>
@@ -251,7 +253,6 @@ static void __fput(struct file *file)
         }
         fops_put(file->f_op);
         put_pid(file->f_owner.pid);
-        file_sb_list_del(file);
         if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
                 i_readcount_dec(inode);
         if (file->f_mode & FMODE_WRITE)
@@ -263,10 +264,77 @@ static void __fput(struct file *file)
         mntput(mnt);
 }
 
+static DEFINE_SPINLOCK(delayed_fput_lock);
+static LIST_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);
+        }
+}
+
+static void ____fput(struct callback_head *work)
+{
+        __fput(container_of(work, struct file, f_u.fu_rcuhead));
+}
+
+/*
+ * If kernel thread really needs to have the final fput() it has done
+ * to complete, call this.  The only user right now is the boot - we
+ * *do* need to make sure our writes to binaries on initramfs has
+ * not left us with opened struct file waiting for __fput() - execve()
+ * won't work without that.  Please, don't add more callers without
+ * very good reasons; in particular, never call that with locks
+ * held and never call that from a thread that might need to do
+ * some work on any kind of umount.
+ */
+void flush_delayed_fput(void)
+{
+        delayed_fput(NULL);
+}
+
+static DECLARE_WORK(delayed_fput_work, delayed_fput);
+
 void fput(struct file *file)
 {
-        if (atomic_long_dec_and_test(&file->f_count))
+        if (atomic_long_dec_and_test(&file->f_count)) {
+                struct task_struct *task = current;
+                file_sb_list_del(file);
+                if (unlikely(in_interrupt() || task->flags & PF_KTHREAD)) {
+                        unsigned long flags;
+                        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);
+                        return;
+                }
+                init_task_work(&file->f_u.fu_rcuhead, ____fput);
+                task_work_add(task, &file->f_u.fu_rcuhead, true);
+        }
+}
+
+/*
+ * synchronous analog of fput(); for kernel threads that might be needed
+ * in some umount() (and thus can't use flush_delayed_fput() without
+ * risking deadlocks), need to wait for completion of __fput() and know
+ * for this specific struct file it won't involve anything that would
+ * need them.  Use only if you really need it - at the very least,
+ * don't blindly convert fput() by kernel thread to that.
+ */
+void __fput_sync(struct file *file)
+{
+        if (atomic_long_dec_and_test(&file->f_count)) {
+                struct task_struct *task = current;
+                file_sb_list_del(file);
+                BUG_ON(!(task->flags & PF_KTHREAD));
                 __fput(file);
+        }
 }
 
 EXPORT_SYMBOL(fput);
@@ -483,10 +551,8 @@ void mark_files_ro(struct super_block *sb)
 {
         struct file *f;
 
-retry:
         lg_global_lock(&files_lglock);
         do_file_list_for_each_entry(sb, f) {
-                struct vfsmount *mnt;
                 if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
                        continue;
                 if (!file_count(f))
@@ -499,12 +565,7 @@ retry:
                 if (file_check_writeable(f) != 0)
                         continue;
                 file_release_write(f);
-                mnt = mntget(f->f_path.mnt);
-                /* This can sleep, so we can't hold the spinlock. */
-                lg_global_unlock(&files_lglock);
-                mnt_drop_write(mnt);
-                mntput(mnt);
-                goto retry;
+                mnt_drop_write_file(f);
         } while_file_list_for_each_entry;
         lg_global_unlock(&files_lglock);
 }