[GFS2] Tidy up meta_io code

Fix a bug in the directory reading code, where we might have dereferenced
a NULL pointer in case of OOM. Updated the directory code to use the new
& improved version of gfs2_meta_ra() which now returns the first block
that was being read. Previously it was releasing it requiring following
code to grab the block again at each point it was called.

Also turned off readahead on directory lookups since we are reading a
hash table, and therefore reading the entries in order is very
unlikely. Readahead is still used for all other calls to the
directory reading function (e.g. when growing the hash table).

Removed the DIO_START constant. Everywhere this was used, it was
used to unconditionally start i/o aside from a couple of places, so
I've removed it and made the couple of exceptions to this rule into
separate functions.

Also hunted through the other DIO flags and removed them as arguments
from functions which were always called with the same combination of
arguments.

Updated gfs2_meta_indirect_buffer to be a bit more efficient and
hopefully also be a bit easier to read.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 76 insertions, 97 deletions

diff --git a/fs/gfs2/meta_io.c b/fs/gfs2/meta_io.c
index 6b52aacb0736..d3708af0a4d1 100644
--- a/fs/gfs2/meta_io.c
+++ b/fs/gfs2/meta_io.c
@@ -273,19 +273,16 @@ void gfs2_meta_inval(struct gfs2_glock *gl)
 /**
  * gfs2_meta_sync - Sync all buffers associated with a glock
  * @gl: The glock
- * @flags: DIO_START | DIO_WAIT
  *
  */
 
-void gfs2_meta_sync(struct gfs2_glock *gl, int flags)
+void gfs2_meta_sync(struct gfs2_glock *gl)
 {
 	struct address_space *mapping = gl->gl_aspace->i_mapping;
-	int error = 0;
+	int error;
 
-	if (flags & DIO_START)
-		filemap_fdatawrite(mapping);
-	if (!error && (flags & DIO_WAIT))
-		error = filemap_fdatawait(mapping);
+	filemap_fdatawrite(mapping);
+	error = filemap_fdatawait(mapping);
 
 	if (error)
 		gfs2_io_error(gl->gl_sbd);
@@ -377,7 +374,7 @@ struct buffer_head *gfs2_meta_new(struct gfs2_glock *gl, u64 blkno)
  * gfs2_meta_read - Read a block from disk
  * @gl: The glock covering the block
  * @blkno: The block number
- * @flags: flags to gfs2_dreread()
+ * @flags: flags
  * @bhp: the place where the buffer is returned (NULL on failure)
  *
  * Returns: errno
@@ -386,45 +383,43 @@ struct buffer_head *gfs2_meta_new(struct gfs2_glock *gl, u64 blkno)
 int gfs2_meta_read(struct gfs2_glock *gl, u64 blkno, int flags,
 		   struct buffer_head **bhp)
 {
-	int error;
-
 	*bhp = getbuf(gl->gl_sbd, gl->gl_aspace, blkno, CREATE);
-	error = gfs2_meta_reread(gl->gl_sbd, *bhp, flags);
-	if (error)
-		brelse(*bhp);
+	if (!buffer_uptodate(*bhp))
+		ll_rw_block(READ, 1, bhp);
+	if (flags & DIO_WAIT) {
+		int error = gfs2_meta_wait(gl->gl_sbd, *bhp);
+		if (error) {
+			brelse(*bhp);
+			return error;
+		}
+	}
 
-	return error;
+	return 0;
 }
 
 /**
- * gfs2_meta_reread - Reread a block from disk
+ * gfs2_meta_wait - Reread a block from disk
  * @sdp: the filesystem
- * @bh: The block to read
- * @flags: Flags that control the read
+ * @bh: The block to wait for
  *
  * Returns: errno
  */
 
-int gfs2_meta_reread(struct gfs2_sbd *sdp, struct buffer_head *bh, int flags)
+int gfs2_meta_wait(struct gfs2_sbd *sdp, struct buffer_head *bh)
 {
 	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
 		return -EIO;
 
-	if ((flags & DIO_START) && !buffer_uptodate(bh))
-		ll_rw_block(READ, 1, &bh);
-
-	if (flags & DIO_WAIT) {
-		wait_on_buffer(bh);
+	wait_on_buffer(bh);
 
-		if (!buffer_uptodate(bh)) {
-			struct gfs2_trans *tr = current->journal_info;
-			if (tr && tr->tr_touched)
-				gfs2_io_error_bh(sdp, bh);
-			return -EIO;
-		}
-		if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
-			return -EIO;
+	if (!buffer_uptodate(bh)) {
+		struct gfs2_trans *tr = current->journal_info;
+		if (tr && tr->tr_touched)
+			gfs2_io_error_bh(sdp, bh);
+		return -EIO;
 	}
+	if (unlikely(test_bit(SDF_SHUTDOWN, &sdp->sd_flags)))
+		return -EIO;
 
 	return 0;
 }
@@ -635,67 +630,57 @@ void gfs2_meta_cache_flush(struct gfs2_inode *ip)
 int gfs2_meta_indirect_buffer(struct gfs2_inode *ip, int height, u64 num,
 			      int new, struct buffer_head **bhp)
 {
-	struct buffer_head *bh, **bh_slot = ip->i_cache + height;
-	int error;
+	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
+	struct gfs2_glock *gl = ip->i_gl;
+	struct buffer_head *bh = NULL, **bh_slot = ip->i_cache + height;
+	int in_cache = 0;
 
 	spin_lock(&ip->i_spin);
-	bh = *bh_slot;
-	if (bh) {
-		if (bh->b_blocknr == num)
-			get_bh(bh);
-		else
-			bh = NULL;
+	if (*bh_slot && (*bh_slot)->b_blocknr == num) {
+		bh = *bh_slot;
+		get_bh(bh);
+		in_cache = 1;
 	}
 	spin_unlock(&ip->i_spin);
 
-	if (bh) {
-		if (new)
-			meta_prep_new(bh);
-		else {
-			error = gfs2_meta_reread(GFS2_SB(&ip->i_inode), bh,
-						 DIO_START | DIO_WAIT);
-			if (error) {
-				brelse(bh);
-				return error;
-			}
-		}
-	} else {
-		if (new)
-			bh = gfs2_meta_new(ip->i_gl, num);
-		else {
-			error = gfs2_meta_read(ip->i_gl, num,
-					       DIO_START | DIO_WAIT, &bh);
-			if (error)
-				return error;
-		}
+	if (!bh)
+		bh = getbuf(gl->gl_sbd, gl->gl_aspace, num, CREATE);
 
-		spin_lock(&ip->i_spin);
-		if (*bh_slot != bh) {
-			brelse(*bh_slot);
-			*bh_slot = bh;
-			get_bh(bh);
-		}
-		spin_unlock(&ip->i_spin);
-	}
+	if (!bh)
+		return -ENOBUFS;
 
 	if (new) {
-		if (gfs2_assert_warn(GFS2_SB(&ip->i_inode), height)) {
-			brelse(bh);
-			return -EIO;
-		}
+		if (gfs2_assert_warn(sdp, height))
+			goto err;
+		meta_prep_new(bh);
 		gfs2_trans_add_bh(ip->i_gl, bh, 1);
 		gfs2_metatype_set(bh, GFS2_METATYPE_IN, GFS2_FORMAT_IN);
 		gfs2_buffer_clear_tail(bh, sizeof(struct gfs2_meta_header));
+	} else {
+		u32 mtype = height ? GFS2_METATYPE_IN : GFS2_METATYPE_DI;
+		if (!buffer_uptodate(bh)) {
+			ll_rw_block(READ, 1, &bh);
+			if (gfs2_meta_wait(sdp, bh))
+				goto err;
+		}
+		if (gfs2_metatype_check(sdp, bh, mtype))
+			goto err;
+	}
 
-	} else if (gfs2_metatype_check(GFS2_SB(&ip->i_inode), bh,
-			     (height) ? GFS2_METATYPE_IN : GFS2_METATYPE_DI)) {
-		brelse(bh);
-		return -EIO;
+	if (!in_cache) {
+		spin_lock(&ip->i_spin);
+		if (*bh_slot)
+			brelse(*bh_slot);
+		*bh_slot = bh;
+		get_bh(bh);
+		spin_unlock(&ip->i_spin);
 	}
 
 	*bhp = bh;
-
 	return 0;
+err:
+	brelse(bh);
+	return -EIO;
 }
 
 /**
@@ -704,19 +689,21 @@ int gfs2_meta_indirect_buffer(struct gfs2_inode *ip, int height, u64 num,
  * @dblock: the starting disk block
  * @extlen: the number of blocks in the extent
  *
+ * returns: the first buffer in the extent
  */
 
-void gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
+struct buffer_head *gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
 {
 	struct gfs2_sbd *sdp = gl->gl_sbd;
 	struct inode *aspace = gl->gl_aspace;
 	struct buffer_head *first_bh, *bh;
 	u32 max_ra = gfs2_tune_get(sdp, gt_max_readahead) >>
 			  sdp->sd_sb.sb_bsize_shift;
-	int error;
 
-	if (!extlen || !max_ra)
-		return;
+	BUG_ON(!extlen);
+
+	if (max_ra < 1)
+		max_ra = 1;
 	if (extlen > max_ra)
 		extlen = max_ra;
 
@@ -724,11 +711,8 @@ void gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
 
 	if (buffer_uptodate(first_bh))
 		goto out;
-	if (!buffer_locked(first_bh)) {
-		error = gfs2_meta_reread(sdp, first_bh, DIO_START);
-		if (error)
-			goto out;
-	}
+	if (!buffer_locked(first_bh))
+		ll_rw_block(READ, 1, &first_bh);
 
 	dblock++;
 	extlen--;
@@ -736,23 +720,18 @@ void gfs2_meta_ra(struct gfs2_glock *gl, u64 dblock, u32 extlen)
 	while (extlen) {
 		bh = getbuf(sdp, aspace, dblock, CREATE);
 
-		if (!buffer_uptodate(bh) && !buffer_locked(bh)) {
-			error = gfs2_meta_reread(sdp, bh, DIO_START);
-			brelse(bh);
-			if (error)
-				goto out;
-		} else
-			brelse(bh);
-
+		if (!buffer_uptodate(bh) && !buffer_locked(bh))
+			ll_rw_block(READA, 1, &bh);
+		brelse(bh);
 		dblock++;
 		extlen--;
-
-		if (buffer_uptodate(first_bh))
-			break;
+		if (!buffer_locked(first_bh) && buffer_uptodate(first_bh))
+			goto out;
 	}
 
+	wait_on_buffer(first_bh);
 out:
-	brelse(first_bh);
+	return first_bh;
 }
 
 /**