fix O_SYNC|O_APPEND syncing the wrong range on write()

It actually goes back to 2004 ([PATCH] Concurrent O_SYNC write support)
when sync_page_range() had been introduced; generic_file_write{,v}() correctly
synced
	pos_after_write - written .. pos_after_write - 1
but generic_file_aio_write() synced
	pos_before_write .. pos_before_write + written - 1
instead.  Which is not the same thing with O_APPEND, obviously.
A couple of years later correct variant had been killed off when
everything switched to use of generic_file_aio_write().

All users of generic_file_aio_write() are affected, and the same bug
has been copied into other instances of ->aio_write().

The fix is trivial; the only subtle point is that generic_write_sync()
ought to be inlined to avoid calculations useless for the majority of
calls.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

5 files changed, 5 insertions, 22 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 853d6d1cc822..a7eda8ebfacc 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2559,8 +2559,8 @@ cifs_writev(struct kiocb *iocb, const struct iovec *iov,
         if (rc > 0) {
                 ssize_t err;
 
-                err = generic_write_sync(file, pos, rc);
-                if (err < 0 && rc > 0)
+                err = generic_write_sync(file, iocb->ki_pos - rc, rc);
+                if (err < 0)
                         rc = err;
         }
 
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 43e64f6022eb..1a5073959f32 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -152,7 +152,7 @@ ext4_file_dio_write(struct kiocb *iocb, const struct iovec *iov,
         if (ret > 0) {
                 ssize_t err;
 
-                err = generic_write_sync(file, pos, ret);
+                err = generic_write_sync(file, iocb->ki_pos - ret, ret);
                 if (err < 0 && ret > 0)
                         ret = err;
         }
diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index ea4ba9daeb47..db9bd8a31725 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -2134,7 +2134,7 @@ static ssize_t ntfs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
         ret = ntfs_file_aio_write_nolock(iocb, iov, nr_segs, &iocb->ki_pos);
         mutex_unlock(&inode->i_mutex);
         if (ret > 0) {
-                int err = generic_write_sync(file, pos, ret);
+                int err = generic_write_sync(file, iocb->ki_pos - ret, ret);
                 if (err < 0)
                         ret = err;
         }
diff --git a/fs/sync.c b/fs/sync.c
index f15537452231..e8ba024a055b 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -222,23 +222,6 @@ SYSCALL_DEFINE1(fdatasync, unsigned int, fd)
         return do_fsync(fd, 1);
 }
 
-/**
- * generic_write_sync - perform syncing after a write if file / inode is sync
- * @file:       file to which the write happened
- * @pos:        offset where the write started
- * @count:      length of the write
- *
- * This is just a simple wrapper about our general syncing function.
- */
-int generic_write_sync(struct file *file, loff_t pos, loff_t count)
-{
-        if (!(file->f_flags & O_DSYNC) && !IS_SYNC(file->f_mapping->host))
-                return 0;
-        return vfs_fsync_range(file, pos, pos + count - 1,
-                               (file->f_flags & __O_SYNC) ? 0 : 1);
-}
-EXPORT_SYMBOL(generic_write_sync);
-
 /*
  * sys_sync_file_range() permits finely controlled syncing over a segment of
  * a file in the range offset .. (offset+nbytes-1) inclusive.  If nbytes is
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 2e7989e3a2d6..64b48eade91d 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -799,7 +799,7 @@ xfs_file_aio_write(
                 XFS_STATS_ADD(xs_write_bytes, ret);
 
                 /* Handle various SYNC-type writes */
-                err = generic_write_sync(file, pos, ret);
+                err = generic_write_sync(file, iocb->ki_pos - ret, ret);
                 if (err < 0)
                         ret = err;
         }