[Devel] [PATCH 2/2] fs: incorrect direct io error handling v8

[Dmitriy Monakhov]

If generic_file_direct_write() has fail (ENOSPC condition) inside
__generic_file_aio_write_nolock() it may have instantiated a few blocks outside
i_size in case of non blockdev files. At least ext2, ext3 and reiserfs interpret
i_size and biggest block difference as error. Later fsck will complain
about wrong i_size. After fsck will fix error i_size will be increased
to the biggest block. This is bad because this blocks contain gurbage
from previous write attempt. And result in silence file data corruption.
This issue affect fs regardless the values of blocksize or pagesize.
We need truncate any block beyond i_size after generic_file_direct_write()
has failed. In fact all existing fs witch use __generic_file_aio_write_nolock()
always call it under i_mutex for non blockdev files. This patch add 
correcspnding BUG_ON() in order to explicitly demand/document it.

Also fix out of date direct_io locking comments.

TEST_CASE:
####TESTCASE_BEGIN
   $touch /mnt/test/BIG_FILE
   ## at this moment /mnt/test/BIG_FILE size and blocks equal to zero
   open("/mnt/test/BIG_FILE", O_WRONLY|O_CREAT|O_DIRECT, 0666) = 3
   write(3, "aaaaaaaaaaaa"..., 104857600) = -1 ENOSPC (No space left on device)
   ## size and block sould't be changed because write op failed.
   $stat /mnt/test/BIG_FILE
     File: `/mnt/test/BIG_FILE'
     Size: 0             Blocks: 110896     IO Block: 1024   regular empty file
   <<<<<<<<<<<<<<<<<<<<<<<<<<<<<^^^^^^^file size is less than biggest block idx
   
   Device: fe07h/65031d    Inode: 14          Links: 1
   Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
   Access: 2007-01-24 20:03:38.000000000 +0300
   Modify: 2007-01-24 20:03:38.000000000 +0300
   Change: 2007-01-24 20:03:39.000000000 +0300
   
   #fsck.ext3 -f /dev/VG/test 
   e2fsck 1.39 (29-May-2006)
   Pass 1: Checking inodes, blocks, and sizes
   Inode 14, i_size is 0, should be 56556544.  Fix<y>? yes
   Pass 2: Checking directory structure
   ....
#####TESTCASE_END

Signed-off-by: Dmitriy Monakhov <dmonakhov at openvz.org>
---
 mm/filemap.c |   24 ++++++++++++++++++++----
 1 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index bbef42f..a08900e 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1892,8 +1892,10 @@ generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
 	/*
 	 * Sync the fs metadata but not the minor inode changes and
 	 * of course not the data as we did direct DMA for the IO.
-	 * i_mutex is held, which protects generic_osync_inode() from
-	 * livelocking.  AIO O_DIRECT ops attempt to sync metadata here.
+	 * i_mutex is held in case of DIO_LOCKING, which protects
+	 * generic_osync_inode() from livelocking. If it is not held, then
+	 * the filesystem must prevent this livelock. AIO O_DIRECT ops
+	 * attempt to sync metadata here.
 	 */
 	if ((written >= 0 || written == -EIOCBQUEUED) &&
 	    ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
@@ -2083,6 +2085,9 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
 	ssize_t		written;
 	ssize_t		err;
 
+	/* Always called under i_mutex for writes to non blockdev files */
+	BUG_ON(!S_ISBLK(inode->i_mode) &&
+			!mutex_is_locked(&inode->i_mutex));
 	ocount = 0;
 	err = generic_iovec_checks(iov, &nr_segs, &ocount, VERIFY_READ);
 	if (err)
@@ -2117,6 +2122,17 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
 
 		written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
 							ppos, count, ocount);
+		/*
+		 * If host is not blockdev generic_file_direct_write() may
+		 * have instantiated a few blocks outside i_size  files
+		 * Trim these off again.
+		 */
+		if (unlikely(written < 0) && !S_ISBLK(inode->i_mode)) {
+			loff_t isize = i_size_read(inode);
+			if (pos + count > isize)
+				vmtruncate(inode, isize);
+		}
+
 		if (written < 0 || written == count)
 			goto out;
 		/*
@@ -2221,8 +2237,8 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 EXPORT_SYMBOL(generic_file_aio_write);
 
 /*
- * Called under i_mutex for writes to S_ISREG files.   Returns -EIO if something
- * went wrong during pagecache shootdown.
+ * Called under i_mutex for writes to S_ISREG files in case of DIO_LOCKING.
+ * Returns -EIO if something went wrong during pagecache shootdown.
  */
 static ssize_t
 generic_file_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
-- 
1.4.4.2