1 files changed, 143 insertions, 7 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 80c819cbe272..aefed9426b03 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -412,6 +412,7 @@ struct inodes_stat_t {
 #include <linux/shrinker.h>
 #include <linux/migrate_mode.h>
 #include <linux/uidgid.h>
+#include <linux/lockdep.h>
 
 #include <asm/byteorder.h>
 
@@ -1439,6 +1440,8 @@ extern void f_delown(struct file *filp);
 extern pid_t f_getown(struct file *filp);
 extern int send_sigurg(struct fown_struct *fown);
 
+struct mm_struct;
+
 /*
  *      Umount options
  */
@@ -1452,6 +1455,32 @@ extern int send_sigurg(struct fown_struct *fown);
 extern struct list_head super_blocks;
 extern spinlock_t sb_lock;
 
+/* Possible states of 'frozen' field */
+enum {
+        SB_UNFROZEN = 0,                /* FS is unfrozen */
+        SB_FREEZE_WRITE = 1,            /* Writes, dir ops, ioctls frozen */
+        SB_FREEZE_TRANS = 2,
+        SB_FREEZE_PAGEFAULT = 2,        /* Page faults stopped as well */
+        SB_FREEZE_FS = 3,               /* For internal FS use (e.g. to stop
+                                         * internal threads if needed) */
+        SB_FREEZE_COMPLETE = 4,         /* ->freeze_fs finished successfully */
+};
+
+#define SB_FREEZE_LEVELS (SB_FREEZE_COMPLETE - 1)
+
+struct sb_writers {
+        /* Counters for counting writers at each level */
+        struct percpu_counter   counter[SB_FREEZE_LEVELS];
+        wait_queue_head_t       wait;           /* queue for waiting for
+                                                   writers / faults to finish */
+        int                     frozen;         /* Is sb frozen? */
+        wait_queue_head_t       wait_unfrozen;  /* queue for waiting for
+                                                   sb to be thawed */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+        struct lockdep_map      lock_map[SB_FREEZE_LEVELS];
+#endif
+};
+
 struct super_block {
         struct list_head        s_list;         /* Keep this first */
         dev_t                   s_dev;          /* search index; _not_ kdev_t */
@@ -1501,6 +1530,7 @@ struct super_block {
 
         int                     s_frozen;
         wait_queue_head_t       s_wait_unfrozen;
+        struct sb_writers       s_writers;
 
         char s_id[32];                          /* Informational name */
         u8 s_uuid[16];                          /* UUID */
@@ -1555,14 +1585,119 @@ extern struct timespec current_fs_time(struct super_block *sb);
 /*
  * Snapshotting support.
  */
-enum {
-        SB_UNFROZEN = 0,
-        SB_FREEZE_WRITE = 1,
-        SB_FREEZE_TRANS = 2,
-};
+/* Will go away when all users are converted */
+#define vfs_check_frozen(sb, level) do { } while (0)
+
+void __sb_end_write(struct super_block *sb, int level);
+int __sb_start_write(struct super_block *sb, int level, bool wait);
+
+/**
+ * sb_end_write - drop write access to a superblock
+ * @sb: the super we wrote to
+ *
+ * Decrement number of writers to the filesystem. Wake up possible waiters
+ * wanting to freeze the filesystem.
+ */
+static inline void sb_end_write(struct super_block *sb)
+{
+        __sb_end_write(sb, SB_FREEZE_WRITE);
+}
+
+/**
+ * sb_end_pagefault - drop write access to a superblock from a page fault
+ * @sb: the super we wrote to
+ *
+ * Decrement number of processes handling write page fault to the filesystem.
+ * Wake up possible waiters wanting to freeze the filesystem.
+ */
+static inline void sb_end_pagefault(struct super_block *sb)
+{
+        __sb_end_write(sb, SB_FREEZE_PAGEFAULT);
+}
+
+/**
+ * sb_end_intwrite - drop write access to a superblock for internal fs purposes
+ * @sb: the super we wrote to
+ *
+ * Decrement fs-internal number of writers to the filesystem.  Wake up possible
+ * waiters wanting to freeze the filesystem.
+ */
+static inline void sb_end_intwrite(struct super_block *sb)
+{
+        __sb_end_write(sb, SB_FREEZE_FS);
+}
+
+/**
+ * sb_start_write - get write access to a superblock
+ * @sb: the super we write to
+ *
+ * When a process wants to write data or metadata to a file system (i.e. dirty
+ * a page or an inode), it should embed the operation in a sb_start_write() -
+ * sb_end_write() pair to get exclusion against file system freezing. This
+ * function increments number of writers preventing freezing. If the file
+ * system is already frozen, the function waits until the file system is
+ * thawed.
+ *
+ * Since freeze protection behaves as a lock, users have to preserve
+ * ordering of freeze protection and other filesystem locks. Generally,
+ * freeze protection should be the outermost lock. In particular, we have:
+ *
+ * sb_start_write
+ *   -> i_mutex                 (write path, truncate, directory ops, ...)
+ *   -> s_umount                (freeze_super, thaw_super)
+ */
+static inline void sb_start_write(struct super_block *sb)
+{
+        __sb_start_write(sb, SB_FREEZE_WRITE, true);
+}
+
+static inline int sb_start_write_trylock(struct super_block *sb)
+{
+        return __sb_start_write(sb, SB_FREEZE_WRITE, false);
+}
+
+/**
+ * sb_start_pagefault - get write access to a superblock from a page fault
+ * @sb: the super we write to
+ *
+ * When a process starts handling write page fault, it should embed the
+ * operation into sb_start_pagefault() - sb_end_pagefault() pair to get
+ * exclusion against file system freezing. This is needed since the page fault
+ * is going to dirty a page. This function increments number of running page
+ * faults preventing freezing. If the file system is already frozen, the
+ * function waits until the file system is thawed.
+ *
+ * Since page fault freeze protection behaves as a lock, users have to preserve
+ * ordering of freeze protection and other filesystem locks. It is advised to
+ * put sb_start_pagefault() close to mmap_sem in lock ordering. Page fault
+ * handling code implies lock dependency:
+ *
+ * mmap_sem
+ *   -> sb_start_pagefault
+ */
+static inline void sb_start_pagefault(struct super_block *sb)
+{
+        __sb_start_write(sb, SB_FREEZE_PAGEFAULT, true);
+}
+
+/*
+ * sb_start_intwrite - get write access to a superblock for internal fs purposes
+ * @sb: the super we write to
+ *
+ * This is the third level of protection against filesystem freezing. It is
+ * free for use by a filesystem. The only requirement is that it must rank
+ * below sb_start_pagefault.
+ *
+ * For example filesystem can call sb_start_intwrite() when starting a
+ * transaction which somewhat eases handling of freezing for internal sources
+ * of filesystem changes (internal fs threads, discarding preallocation on file
+ * close, etc.).
+ */
+static inline void sb_start_intwrite(struct super_block *sb)
+{
+        __sb_start_write(sb, SB_FREEZE_FS, true);
+}
 
-#define vfs_check_frozen(sb, level) \
-        wait_event((sb)->s_wait_unfrozen, ((sb)->s_frozen < (level)))
 
 extern bool inode_owner_or_capable(const struct inode *inode);
 
@@ -1886,6 +2021,7 @@ struct file_system_type {
         struct lock_class_key s_lock_key;
         struct lock_class_key s_umount_key;
         struct lock_class_key s_vfs_rename_key;
+        struct lock_class_key s_writers_key[SB_FREEZE_LEVELS];
 
         struct lock_class_key i_lock_key;
         struct lock_class_key i_mutex_key;