1 files changed, 105 insertions, 17 deletions

diff --git a/fs/sync.c b/fs/sync.c
index 7abc65fbf21d..3422ba61d86d 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -13,38 +13,128 @@
 #include <linux/pagemap.h>
 #include <linux/quotaops.h>
 #include <linux/buffer_head.h>
+#include "internal.h"
 
 #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.
+ * 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 void do_sync(unsigned long wait)
+static int __sync_filesystem(struct super_block *sb, int wait)
 {
-        wakeup_pdflush(0);
-        sync_inodes(0);         /* All mappings, inodes and their blockdevs */
-        vfs_dq_sync(NULL);
-        sync_supers();          /* Write the superblocks */
-        sync_filesystems(0);    /* Start syncing the filesystems */
-        sync_filesystems(wait); /* Waitingly sync the filesystems */
-        sync_inodes(wait);      /* Mappings, inodes and blockdevs, again. */
+        /* Avoid doing twice syncing and cache pruning for quota sync */
         if (!wait)
-                printk("Emergency Sync complete\n");
-        if (unlikely(laptop_mode))
-                laptop_sync_completion();
+                writeout_quota_sb(sb, -1);
+        else
+                sync_quota_sb(sb, -1);
+        sync_inodes_sb(sb, wait);
+        if (sb->s_op->sync_fs)
+                sb->s_op->sync_fs(sb, wait);
+        return __sync_blockdev(sb->s_bdev, wait);
+}
+
+/*
+ * 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.
+ */
+int sync_filesystem(struct super_block *sb)
+{
+        int ret;
+
+        /*
+         * We need to be protected against the filesystem going from
+         * r/o to r/w or vice versa.
+         */
+        WARN_ON(!rwsem_is_locked(&sb->s_umount));
+
+        /*
+         * No point in syncing out anything if the filesystem is read-only.
+         */
+        if (sb->s_flags & MS_RDONLY)
+                return 0;
+
+        ret = __sync_filesystem(sb, 0);
+        if (ret < 0)
+                return ret;
+        return __sync_filesystem(sb, 1);
+}
+EXPORT_SYMBOL_GPL(sync_filesystem);
+
+/*
+ * 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
+ * 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
+ * flags again, which will cause process A to resync everything.  Fix that with
+ * a local mutex.
+ */
+static void sync_filesystems(int wait)
+{
+        struct super_block *sb;
+        static DEFINE_MUTEX(mutex);
+
+        mutex_lock(&mutex);             /* Could be down_interruptible */
+        spin_lock(&sb_lock);
+        list_for_each_entry(sb, &super_blocks, s_list)
+                sb->s_need_sync = 1;
+
+restart:
+        list_for_each_entry(sb, &super_blocks, s_list) {
+                if (!sb->s_need_sync)
+                        continue;
+                sb->s_need_sync = 0;
+                sb->s_count++;
+                spin_unlock(&sb_lock);
+
+                down_read(&sb->s_umount);
+                if (!(sb->s_flags & MS_RDONLY) && sb->s_root)
+                        __sync_filesystem(sb, wait);
+                up_read(&sb->s_umount);
+
+                /* restart only when sb is no longer on the list */
+                spin_lock(&sb_lock);
+                if (__put_super_and_need_restart(sb))
+                        goto restart;
+        }
+        spin_unlock(&sb_lock);
+        mutex_unlock(&mutex);
 }
 
+/*
+ * sync everything.  Start out by waking pdflush, because that writes back
+ * all queues in parallel.
+ */
 SYSCALL_DEFINE0(sync)
 {
-        do_sync(1);
+        wakeup_pdflush(0);
+        sync_filesystems(0);
+        sync_filesystems(1);
+        if (unlikely(laptop_mode))
+                laptop_sync_completion();
         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);
 }
 
@@ -75,10 +165,8 @@ int file_fsync(struct file *filp, struct dentry *dentry, int datasync)
 
         /* sync the superblock to buffers */
         sb = inode->i_sb;
-        lock_super(sb);
         if (sb->s_dirt && sb->s_op->write_super)
                 sb->s_op->write_super(sb);
-        unlock_super(sb);
 
         /* .. finally sync the buffers to disk */
         err = sync_blockdev(sb->s_bdev);