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>

1 files changed, 10 insertions, 21 deletions

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);
 }