Revert "writeback: do not sync data dirtied after sync start"

This reverts commit c4a391b53a72d2df4ee97f96f78c1d5971b47489. Dave
Chinner <david@fromorbit.com> has reported the commit may cause some
inodes to be left out from sync(2). This is because we can call
redirty_tail() for some inode (which sets i_dirtied_when to current time)
after sync(2) has started or similarly requeue_inode() can set
i_dirtied_when to current time if writeback had to skip some pages. The
real problem is in the functions clobbering i_dirtied_when but fixing
that isn't trivial so revert is a safer choice for now.

CC: stable@vger.kernel.org # >= 3.13
Signed-off-by: Jan Kara <jack@suse.cz>

5 files changed, 22 insertions, 36 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index e0259a163f98..d754e3cf99a8 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -40,18 +40,13 @@
 struct wb_writeback_work {
         long nr_pages;
         struct super_block *sb;
-        /*
-         * Write only inodes dirtied before this time. Don't forget to set
-         * older_than_this_is_set when you set this.
-         */
-        unsigned long older_than_this;
+        unsigned long *older_than_this;
         enum writeback_sync_modes sync_mode;
         unsigned int tagged_writepages:1;
         unsigned int for_kupdate:1;
         unsigned int range_cyclic:1;
         unsigned int for_background:1;
         unsigned int for_sync:1;        /* sync(2) WB_SYNC_ALL writeback */
-        unsigned int older_than_this_is_set:1;
         enum wb_reason reason;          /* why was writeback initiated? */
 
         struct list_head list;          /* pending work list */
@@ -252,10 +247,10 @@ static int move_expired_inodes(struct list_head *delaying_queue,
         int do_sb_sort = 0;
         int moved = 0;
 
-        WARN_ON_ONCE(!work->older_than_this_is_set);
         while (!list_empty(delaying_queue)) {
                 inode = wb_inode(delaying_queue->prev);
-                if (inode_dirtied_after(inode, work->older_than_this))
+                if (work->older_than_this &&
+                    inode_dirtied_after(inode, *work->older_than_this))
                         break;
                 list_move(&inode->i_wb_list, &tmp);
                 moved++;
@@ -742,8 +737,6 @@ static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
                 .sync_mode      = WB_SYNC_NONE,
                 .range_cyclic   = 1,
                 .reason         = reason,
-                .older_than_this = jiffies,
-                .older_than_this_is_set = 1,
         };
 
         spin_lock(&wb->list_lock);
@@ -802,13 +795,12 @@ static long wb_writeback(struct bdi_writeback *wb,
 {
         unsigned long wb_start = jiffies;
         long nr_pages = work->nr_pages;
+        unsigned long oldest_jif;
         struct inode *inode;
         long progress;
 
-        if (!work->older_than_this_is_set) {
-                work->older_than_this = jiffies;
-                work->older_than_this_is_set = 1;
-        }
+        oldest_jif = jiffies;
+        work->older_than_this = &oldest_jif;
 
         spin_lock(&wb->list_lock);
         for (;;) {
@@ -842,10 +834,10 @@ static long wb_writeback(struct bdi_writeback *wb,
                  * safe.
                  */
                 if (work->for_kupdate) {
-                        work->older_than_this = jiffies -
+                        oldest_jif = jiffies -
                                 msecs_to_jiffies(dirty_expire_interval * 10);
                 } else if (work->for_background)
-                        work->older_than_this = jiffies;
+                        oldest_jif = jiffies;
 
                 trace_writeback_start(wb->bdi, work);
                 if (list_empty(&wb->b_io))
@@ -1357,21 +1349,18 @@ EXPORT_SYMBOL(try_to_writeback_inodes_sb);
 
 /**
  * sync_inodes_sb       -       sync sb inode pages
- * @sb:                 the superblock
- * @older_than_this:    timestamp
+ * @sb: the superblock
  *
  * This function writes and waits on any dirty inode belonging to this
- * superblock that has been dirtied before given timestamp.
+ * super_block.
  */
-void sync_inodes_sb(struct super_block *sb, unsigned long older_than_this)
+void sync_inodes_sb(struct super_block *sb)
 {
         DECLARE_COMPLETION_ONSTACK(done);
         struct wb_writeback_work work = {
                 .sb             = sb,
                 .sync_mode      = WB_SYNC_ALL,
                 .nr_pages       = LONG_MAX,
-                .older_than_this = older_than_this,
-                .older_than_this_is_set = 1,
                 .range_cyclic   = 0,
                 .done           = &done,
                 .reason         = WB_REASON_SYNC,
diff --git a/fs/sync.c b/fs/sync.c
index e8ba024a055b..b28d1dd10e8b 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -27,11 +27,10 @@
  * 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 __sync_filesystem(struct super_block *sb, int wait,
-                             unsigned long start)
+static int __sync_filesystem(struct super_block *sb, int wait)
 {
         if (wait)
-                sync_inodes_sb(sb, start);
+                sync_inodes_sb(sb);
         else
                 writeback_inodes_sb(sb, WB_REASON_SYNC);
 
@@ -48,7 +47,6 @@ static int __sync_filesystem(struct super_block *sb, int wait,
 int sync_filesystem(struct super_block *sb)
 {
         int ret;
-        unsigned long start = jiffies;
 
         /*
          * We need to be protected against the filesystem going from
@@ -62,17 +60,17 @@ int sync_filesystem(struct super_block *sb)
         if (sb->s_flags & MS_RDONLY)
                 return 0;
 
-        ret = __sync_filesystem(sb, 0, start);
+        ret = __sync_filesystem(sb, 0);
         if (ret < 0)
                 return ret;
-        return __sync_filesystem(sb, 1, start);
+        return __sync_filesystem(sb, 1);
 }
 EXPORT_SYMBOL_GPL(sync_filesystem);
 
 static void sync_inodes_one_sb(struct super_block *sb, void *arg)
 {
         if (!(sb->s_flags & MS_RDONLY))
-                sync_inodes_sb(sb, *((unsigned long *)arg));
+                sync_inodes_sb(sb);
 }
 
 static void sync_fs_one_sb(struct super_block *sb, void *arg)
@@ -104,10 +102,9 @@ static void fdatawait_one_bdev(struct block_device *bdev, void *arg)
 SYSCALL_DEFINE0(sync)
 {
         int nowait = 0, wait = 1;
-        unsigned long start = jiffies;
 
         wakeup_flusher_threads(0, WB_REASON_SYNC);
-        iterate_supers(sync_inodes_one_sb, &start);
+        iterate_supers(sync_inodes_one_sb, NULL);
         iterate_supers(sync_fs_one_sb, &nowait);
         iterate_supers(sync_fs_one_sb, &wait);
         iterate_bdevs(fdatawrite_one_bdev, NULL);
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index f317488263dd..d971f4932b5d 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -913,7 +913,7 @@ xfs_flush_inodes(
         struct super_block      *sb = mp->m_super;
 
         if (down_read_trylock(&sb->s_umount)) {
-                sync_inodes_sb(sb, jiffies);
+                sync_inodes_sb(sb);
                 up_read(&sb->s_umount);
         }
 }
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index fc0e4320aa6d..021b8a319b9e 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -97,7 +97,7 @@ void writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
 int try_to_writeback_inodes_sb(struct super_block *, enum wb_reason reason);
 int try_to_writeback_inodes_sb_nr(struct super_block *, unsigned long nr,
                                   enum wb_reason reason);
-void sync_inodes_sb(struct super_block *sb, unsigned long older_than_this);
+void sync_inodes_sb(struct super_block *);
 void wakeup_flusher_threads(long nr_pages, enum wb_reason reason);
 void inode_wait_for_writeback(struct inode *inode);
 
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index c7bbbe794e65..464ea82e10db 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -287,11 +287,11 @@ TRACE_EVENT(writeback_queue_io,
                 __field(int,            reason)
         ),
         TP_fast_assign(
-                unsigned long older_than_this = work->older_than_this;
+                unsigned long *older_than_this = work->older_than_this;
                 strncpy(__entry->name, dev_name(wb->bdi->dev), 32);
-                __entry->older  = older_than_this;
+                __entry->older  = older_than_this ?  *older_than_this : 0;
                 __entry->age    = older_than_this ?
-                                  (jiffies - older_than_this) * 1000 / HZ : -1;
+                                  (jiffies - *older_than_this) * 1000 / HZ : -1;
                 __entry->moved  = moved;
                 __entry->reason = work->reason;
         ),