vfs: Make sys_sync() use fsync_super() (version 4)

It is unnecessarily fragile to have two places (fsync_super() and do_sync())
doing data integrity sync of the filesystem. Alter __fsync_super() to
accommodate needs of both callers and use it. So after this patch
__fsync_super() is the only place where we gather all the calls needed to
properly send all data on a filesystem to disk.

Nice bonus is that we get a complete livelock avoidance and write_supers()
is now only used for periodic writeback of superblocks.

sync_blockdevs() introduced a couple of patches ago is gone now.

[build fixes folded]

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

5 files changed, 50 insertions, 133 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index fe47f7227618..4b6a3b9d01ef 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -176,17 +176,22 @@ blkdev_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
                                 iov, offset, nr_segs, blkdev_get_blocks, NULL);
 }
 
+int __sync_blockdev(struct block_device *bdev, int wait)
+{
+        if (!bdev)
+                return 0;
+        if (!wait)
+                return filemap_flush(bdev->bd_inode->i_mapping);
+        return filemap_write_and_wait(bdev->bd_inode->i_mapping);
+}
+
 /*
  * Write out and wait upon all the dirty data associated with a block
  * device via its mapping.  Does not take the superblock lock.
  */
 int sync_blockdev(struct block_device *bdev)
 {
-        int ret = 0;
-
-        if (bdev)
-                ret = filemap_write_and_wait(bdev->bd_inode->i_mapping);
-        return ret;
+        return __sync_blockdev(bdev, 1);
 }
 EXPORT_SYMBOL(sync_blockdev);
 
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 91013ff7dd53..e0fb2e789598 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -679,55 +679,6 @@ void sync_inodes_sb(struct super_block *sb, int wait)
 }
 
 /**
- * sync_inodes - writes all inodes to disk
- * @wait: wait for completion
- *
- * sync_inodes() goes through each super block's dirty inode list, writes the
- * inodes out, waits on the writeout and puts the inodes back on the normal
- * list.
- *
- * This is for sys_sync().  fsync_dev() uses the same algorithm.  The subtle
- * part of the sync functions is that the blockdev "superblock" is processed
- * last.  This is because the write_inode() function of a typical fs will
- * perform no I/O, but will mark buffers in the blockdev mapping as dirty.
- * What we want to do is to perform all that dirtying first, and then write
- * back all those inode blocks via the blockdev mapping in one sweep.  So the
- * additional (somewhat redundant) sync_blockdev() calls here are to make
- * sure that really happens.  Because if we call sync_inodes_sb(wait=1) with
- * outstanding dirty inodes, the writeback goes block-at-a-time within the
- * filesystem's write_inode().  This is extremely slow.
- */
-static void __sync_inodes(int wait)
-{
-        struct super_block *sb;
-
-        spin_lock(&sb_lock);
-restart:
-        list_for_each_entry(sb, &super_blocks, s_list) {
-                sb->s_count++;
-                spin_unlock(&sb_lock);
-                down_read(&sb->s_umount);
-                if (sb->s_root) {
-                        sync_inodes_sb(sb, wait);
-                        sync_blockdev(sb->s_bdev);
-                }
-                up_read(&sb->s_umount);
-                spin_lock(&sb_lock);
-                if (__put_super_and_need_restart(sb))
-                        goto restart;
-        }
-        spin_unlock(&sb_lock);
-}
-
-void sync_inodes(int wait)
-{
-        __sync_inodes(0);
-
-        if (wait)
-                __sync_inodes(1);
-}
-
-/**
  * write_inode_now      -       write an inode to disk
  * @inode: inode to write to disk
  * @sync: whether the write should be synchronous or not
diff --git a/fs/internal.h b/fs/internal.h
index 343a537ab809..dbec3cc28338 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -25,6 +25,8 @@ static inline int sb_is_blkdev_sb(struct super_block *sb)
         return sb == blockdev_superblock;
 }
 
+extern int __sync_blockdev(struct block_device *bdev, int wait);
+
 #else
 static inline void bdev_cache_init(void)
 {
@@ -34,6 +36,11 @@ static inline int sb_is_blkdev_sb(struct super_block *sb)
 {
         return 0;
 }
+
+static inline int __sync_blockdev(struct block_device *bdev, int wait)
+{
+        return 0;
+}
 #endif
 
 /*
@@ -71,12 +78,3 @@ extern void chroot_fs_refs(struct path *, struct path *);
  * file_table.c
  */
 extern void mark_files_ro(struct super_block *);
-
-/*
- * super.c
- */
-#ifdef CONFIG_BLOCK
-extern void sync_blockdevs(void);
-#else
-static inline void sync_blockdevs(void) { }
-#endif
diff --git a/fs/super.c b/fs/super.c
index 8dbe1ead9ddd..c8ce5ed04249 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -284,23 +284,23 @@ EXPORT_SYMBOL(lock_super);
 EXPORT_SYMBOL(unlock_super);
 
 /*
- * Write out and wait upon all dirty data associated with this
- * superblock.  Filesystem data as well as the underlying block
- * device.  Takes the superblock lock.  Requires a second blkdev
- * flush by the caller to complete the operation.
+ * Do the filesystem syncing work. For simple filesystems sync_inodes_sb(sb, 0)
+ * just dirties buffers with inodes so we have to submit IO for these buffers
+ * via __sync_blockdev(). This also speeds up the wait == 1 case since in that
+ * case write_inode() functions do sync_dirty_buffer() and thus effectively
+ * write one block at a time.
  */
-static int __fsync_super(struct super_block *sb)
+static int __fsync_super(struct super_block *sb, int wait)
 {
-        sync_inodes_sb(sb, 0);
         vfs_dq_sync(sb);
-        sync_inodes_sb(sb, 1);
+        sync_inodes_sb(sb, wait);
         lock_super(sb);
         if (sb->s_dirt && sb->s_op->write_super)
                 sb->s_op->write_super(sb);
         unlock_super(sb);
         if (sb->s_op->sync_fs)
-                sb->s_op->sync_fs(sb, 1);
-        return sync_blockdev(sb->s_bdev);
+                sb->s_op->sync_fs(sb, wait);
+        return __sync_blockdev(sb->s_bdev, wait);
 }
 
 /*
@@ -310,7 +310,12 @@ static int __fsync_super(struct super_block *sb)
  */
 int fsync_super(struct super_block *sb)
 {
-        return __fsync_super(sb);
+        int ret;
+
+        ret = __fsync_super(sb, 0);
+        if (ret < 0)
+                return ret;
+        return __fsync_super(sb, 1);
 }
 EXPORT_SYMBOL_GPL(fsync_super);
 
@@ -469,20 +474,18 @@ restart:
 }
 
 /*
- * Call the ->sync_fs super_op against all filesystems which are r/w and
- * which implement it.
+ * Sync all the data for all the filesystems (called by sys_sync() and
+ * emergency sync)
  *
  * This operation is careful to avoid the livelock which could easily happen
- * if two or more filesystems are being continuously dirtied.  s_need_sync_fs
+ * if two or more filesystems are being continuously dirtied.  s_need_sync
  * is used only here.  We set it against all filesystems and then clear it as
  * we sync them.  So redirtied filesystems are skipped.
  *
  * But if process A is currently running sync_filesystems and then process B
- * calls sync_filesystems as well, process B will set all the s_need_sync_fs
+ * calls sync_filesystems as well, process B will set all the s_need_sync
  * flags again, which will cause process A to resync everything.  Fix that with
  * a local mutex.
- *
- * (Fabian) Avoid sync_fs with clean fs & wait mode 0
  */
 void sync_filesystems(int wait)
 {
@@ -492,25 +495,23 @@ void sync_filesystems(int wait)
         mutex_lock(&mutex);             /* Could be down_interruptible */
         spin_lock(&sb_lock);
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (!sb->s_op->sync_fs)
-                        continue;
                 if (sb->s_flags & MS_RDONLY)
                         continue;
-                sb->s_need_sync_fs = 1;
+                sb->s_need_sync = 1;
         }
 
 restart:
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (!sb->s_need_sync_fs)
+                if (!sb->s_need_sync)
                         continue;
-                sb->s_need_sync_fs = 0;
+                sb->s_need_sync = 0;
                 if (sb->s_flags & MS_RDONLY)
                         continue;       /* hm.  Was remounted r/o meanwhile */
                 sb->s_count++;
                 spin_unlock(&sb_lock);
                 down_read(&sb->s_umount);
                 if (sb->s_root)
-                        sb->s_op->sync_fs(sb, wait);
+                        __fsync_super(sb, wait);
                 up_read(&sb->s_umount);
                 /* restart only when sb is no longer on the list */
                 spin_lock(&sb_lock);
@@ -521,33 +522,6 @@ restart:
         mutex_unlock(&mutex);
 }
 
-#ifdef CONFIG_BLOCK
-/*
- *  Sync all block devices underlying some superblock
- */
-void sync_blockdevs(void)
-{
-        struct super_block *sb;
-
-        spin_lock(&sb_lock);
-restart:
-        list_for_each_entry(sb, &super_blocks, s_list) {
-                if (!sb->s_bdev)
-                        continue;
-                sb->s_count++;
-                spin_unlock(&sb_lock);
-                down_read(&sb->s_umount);
-                if (sb->s_root)
-                        sync_blockdev(sb->s_bdev);
-                up_read(&sb->s_umount);
-                spin_lock(&sb_lock);
-                if (__put_super_and_need_restart(sb))
-                        goto restart;
-        }
-        spin_unlock(&sb_lock);
-}
-#endif
-
 /**
  *      get_super - get the superblock of a device
  *      @bdev: device to get the superblock for
diff --git a/fs/sync.c b/fs/sync.c
index 631fd5aece78..be0798cc33d7 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -18,35 +18,24 @@
 #define VALID_FLAGS (SYNC_FILE_RANGE_WAIT_BEFORE|SYNC_FILE_RANGE_WRITE| \
                         SYNC_FILE_RANGE_WAIT_AFTER)
 
-/*
- * sync everything.  Start out by waking pdflush, because that writes back
- * all queues in parallel.
- */
-static void do_sync(unsigned long wait)
+SYSCALL_DEFINE0(sync)
 {
-        wakeup_pdflush(0);
-        sync_inodes(0);         /* All mappings, inodes and their blockdevs */
-        vfs_dq_sync(NULL);
-        sync_inodes(wait);      /* Mappings, inodes and blockdevs, again. */
-        sync_supers();          /* Write the superblocks */
-        sync_filesystems(0);    /* Start syncing the filesystems */
-        sync_filesystems(wait); /* Waitingly sync the filesystems */
-        sync_blockdevs();
-        if (!wait)
-                printk("Emergency Sync complete\n");
+        sync_filesystems(0);
+        sync_filesystems(1);
         if (unlikely(laptop_mode))
                 laptop_sync_completion();
-}
-
-SYSCALL_DEFINE0(sync)
-{
-        do_sync(1);
         return 0;
 }
 
 static void do_sync_work(struct work_struct *work)
 {
-        do_sync(0);
+        /*
+         * Sync twice to reduce the possibility we skipped some inodes / pages
+         * because they were temporarily locked
+         */
+        sync_filesystems(0);
+        sync_filesystems(0);
+        printk("Emergency Sync complete\n");
         kfree(work);
 }