ext4: Resolve the hang of direct i/o read in handling EXT4_IO_END_UNWRITTEN.

EXT4_IO_END_UNWRITTEN flag set and the increase of i_aiodio_unwritten
should be done simultaneously since ext4_end_io_nolock always clear
the flag and decrease the counter in the same time.

We don't increase i_aiodio_unwritten when setting
EXT4_IO_END_UNWRITTEN so it will go nagative and causes some process
to wait forever.

Part of the patch came from Eric in his e-mail, but it doesn't fix the
problem met by Michael actually.

http://marc.info/?l=linux-ext4&m=131316851417460&w=2

Reported-and-Tested-by: Michael Tokarev<mjt@tls.msk.ru>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Tao Ma <boyu.mt@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

2 files changed, 12 insertions, 3 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7dd698107822..762e8037c888 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2678,8 +2678,15 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
                 goto out;
         }
 
-        io_end->flag = EXT4_IO_END_UNWRITTEN;
+        /*
+         * It may be over-defensive here to check EXT4_IO_END_UNWRITTEN now,
+         * but being more careful is always safe for the future change.
+         */
         inode = io_end->inode;
+        if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
+                io_end->flag |= EXT4_IO_END_UNWRITTEN;
+                atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
+        }
 
         /* Add the io_end to per-inode completed io list*/
         spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 430c401d0895..78839af7ce29 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c
@@ -334,8 +334,10 @@ submit_and_retry:
         if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
             (io_end->pages[io_end->num_io_pages-1] != io_page))
                 goto submit_and_retry;
-        if (buffer_uninit(bh))
-                io->io_end->flag |= EXT4_IO_END_UNWRITTEN;
+        if (buffer_uninit(bh) && !(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
+                io_end->flag |= EXT4_IO_END_UNWRITTEN;
+                atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
+        }
         io->io_end->size += bh->b_size;
         io->io_next_block++;
         ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));