[PATCH] mm: be sure to trim blocks after direct_io has failed

[Dmitriy Monakhov <dmonakhov@openvz.org>]

This is updated version of patch aimed to fix direct_io error handling issue
i've previously sent 2 wheeks ago. If you don't like anything in this patch
plese let me know.

Changes:
  - comments added. I think now it is clearly describe things.
  - patch prepared against 2.6.20-mm2

How this patch tested:
  - LTP test, and other readv/writev op tests.
  - fsstress test.
  - manual direct_io tests.

Log:
 - Move common segment checks to separate helper function.
 - Trim off blocks after generic_file_direct_write() has failed.
 - Update out of date comments about direct_io locking rules.

Signed-off-by: Monakhov Dmitriy <dmonakhov@openvz.org>
---
 mm/filemap.c |  107 +++++++++++++++++++++++++++++++++++----------------------
 1 files changed, 66 insertions(+), 41 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index a9284c2..c81184c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1147,6 +1147,38 @@ success:
 	return size;
 }
 
+/*
+ * Performs necessary checks before doing a write
+ *
+ * Adjust number of segments and amount of bytes to write.
+ * Returns appropriate error code that caller should return or
+ * zero in case that write should be allowed.
+ */
+int generic_segment_checks(const struct iovec *iov, unsigned long *nr_segs,
+		size_t *count, unsigned long access_flags)
+{
+	unsigned long   seg;
+	for (seg = 0; seg < *nr_segs; seg++) {
+		const struct iovec *iv = &iov[seg];
+
+		/*
+		 * If any segment has a negative length, or the cumulative
+		 * length ever wraps negative then return -EINVAL.
+		 */
+		*count += iv->iov_len;
+		if (unlikely((ssize_t)(*count|iv->iov_len) < 0))
+			return -EINVAL;
+		if (access_ok(access_flags, iv->iov_base, iv->iov_len))
+			continue;
+		if (seg == 0)
+			return -EFAULT;
+		*nr_segs = seg;
+		*count -= iv->iov_len;	/* This segment is no good */
+		break;
+	}
+	return 0;
+}
+
 /**
  * generic_file_aio_read - generic filesystem read routine
  * @iocb:	kernel I/O control block
@@ -1168,24 +1200,9 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
 	loff_t *ppos = &iocb->ki_pos;
 
 	count = 0;
-	for (seg = 0; seg < nr_segs; seg++) {
-		const struct iovec *iv = &iov[seg];
-
-		/*
-		 * If any segment has a negative length, or the cumulative
-		 * length ever wraps negative then return -EINVAL.
-		 */
-		count += iv->iov_len;
-		if (unlikely((ssize_t)(count|iv->iov_len) < 0))
-			return -EINVAL;
-		if (access_ok(VERIFY_WRITE, iv->iov_base, iv->iov_len))
-			continue;
-		if (seg == 0)
-			return -EFAULT;
-		nr_segs = seg;
-		count -= iv->iov_len;	/* This segment is no good */
-		break;
-	}
+	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
+	if (retval)
+		return retval;
 
 	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
 	if (filp->f_flags & O_DIRECT) {
@@ -2080,8 +2097,9 @@ 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 may not being held, if so some specific locking
+	 * ordering must protect generic_osync_inode() from livelocking.
+	 * AIO O_DIRECT ops attempt to sync metadata here.
 	 */
 	if ((written >= 0 || written == -EIOCBQUEUED) &&
 	    ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
@@ -2271,30 +2289,14 @@ __generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
 	size_t ocount;		/* original count */
 	size_t count;		/* after file limit checks */
 	struct inode 	*inode = mapping->host;
-	unsigned long	seg;
 	loff_t		pos;
 	ssize_t		written;
 	ssize_t		err;
 
 	ocount = 0;
-	for (seg = 0; seg < nr_segs; seg++) {
-		const struct iovec *iv = &iov[seg];
-
-		/*
-		 * If any segment has a negative length, or the cumulative
-		 * length ever wraps negative then return -EINVAL.
-		 */
-		ocount += iv->iov_len;
-		if (unlikely((ssize_t)(ocount|iv->iov_len) < 0))
-			return -EINVAL;
-		if (access_ok(VERIFY_READ, iv->iov_base, iv->iov_len))
-			continue;
-		if (seg == 0)
-			return -EFAULT;
-		nr_segs = seg;
-		ocount -= iv->iov_len;	/* This segment is no good */
-		break;
-	}
+	err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
+	if (err)
+		return err;
 	if (unlikely(aio_restarted())) {
 		/* nothing to transfer, may just need to sync data */
 		return ocount;
@@ -2420,6 +2422,29 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	mutex_lock(&inode->i_mutex);
 	ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
 			&iocb->ki_pos);
+	/* 
+	 * If __generic_file_aio_write_nolock has failed.
+	 * This may happen because of:
+	 * 1) Bad segment found (failed before actual write attempt)
+	 * 2) Segments are good, but actual write operation failed
+	 *    and may have instantiated a few blocks outside i_size.
+	 *   a) in case of buffered write these blocks was already
+	 *   	trimmed by generic_file_buffered_write()
+	 *   b) in case of O_DIRECT these blocks weren't trimmed yet.
+	 *
+	 * In case of (2b) these blocks have to be trimmed off again.
+	 */
+	if (unlikely( ret < 0 && file->f_flags & O_DIRECT)) {
+		unsigned long nr_segs_avail = nr_segs;
+		size_t count = 0;
+		if (!generic_segment_checks(iov, &nr_segs_avail, &count,
+				VERIFY_READ)) {
+			/*It is (2b) case, because segments are good*/
+			loff_t isize = i_size_read(inode);
+			if (pos + count > isize)
+				vmtruncate(inode, isize);
+		}
+	}
 	mutex_unlock(&inode->i_mutex);
 
 	if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
@@ -2436,8 +2461,8 @@ 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.
+ * May be called without i_mutex for writes to S_ISREG files.
+ * 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,
-- 
1.5.0.1