ext4: fix partial cluster initialization

The partial_cluster variable is not always initialized correctly when
hole punching on bigalloc file systems.  Although commit c06344939422
("ext4: fix partial cluster handling for bigalloc file systems")
addressed the case where the right edge of the punched region and the
next extent to its right were within the same leaf, it didn't handle
the case where the next extent to its right is in the next leaf.  This
causes xfstest generic/300 to fail.

Fix this by replacing the code in c0634493922 with a more general
solution that can continue the search for the first cluster to the
right of the punched region into the next leaf if present.  If found,
partial_cluster is initialized to this cluster's negative value.
There's no need to determine if that cluster is actually shared;  we
simply record it so its blocks won't be freed in the event it does
happen to be shared.

Also, minimize the burden on non-bigalloc file systems with some minor
code simplification.

Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

@@ -2621,27 +2621,6 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
 	ex_ee_block = le32_to_cpu(ex->ee_block);
 	ex_ee_len = ext4_ext_get_actual_len(ex);
 
-	/*
-	 * If we're starting with an extent other than the last one in the
-	 * node, we need to see if it shares a cluster with the extent to
-	 * the right (towards the end of the file). If its leftmost cluster
-	 * is this extent's rightmost cluster and it is not cluster aligned,
-	 * we'll mark it as a partial that is not to be deallocated.
-	 */
-
-	if (ex != EXT_LAST_EXTENT(eh)) {
-		ext4_fsblk_t current_pblk, right_pblk;
-		long long current_cluster, right_cluster;
-
-		current_pblk = ext4_ext_pblock(ex) + ex_ee_len - 1;
-		current_cluster = (long long)EXT4_B2C(sbi, current_pblk);
-		right_pblk = ext4_ext_pblock(ex + 1);
-		right_cluster = (long long)EXT4_B2C(sbi, right_pblk);
-		if (current_cluster == right_cluster &&
-			EXT4_PBLK_COFF(sbi, right_pblk))
-			*partial_cluster = -right_cluster;
-	}
-
 	trace_ext4_ext_rm_leaf(inode, start, ex, *partial_cluster);
 
 	while (ex >= EXT_FIRST_EXTENT(eh) &&
@@ -2666,14 +2645,16 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
 		if (end < ex_ee_block) {
 			/*
 			 * We're going to skip this extent and move to another,
-			 * so if this extent is not cluster aligned we have
-			 * to mark the current cluster as used to avoid
-			 * accidentally freeing it later on
+			 * so note that its first cluster is in use to avoid
+			 * freeing it when removing blocks.  Eventually, the
+			 * right edge of the truncated/punched region will
+			 * be just to the left.
 			 */
-			pblk = ext4_ext_pblock(ex);
-			if (EXT4_PBLK_COFF(sbi, pblk))
+			if (sbi->s_cluster_ratio > 1) {
+				pblk = ext4_ext_pblock(ex);
 				*partial_cluster =
-					-((long long)EXT4_B2C(sbi, pblk));
+					-(long long) EXT4_B2C(sbi, pblk);
+			}
 			ex--;
 			ex_ee_block = le32_to_cpu(ex->ee_block);
 			ex_ee_len = ext4_ext_get_actual_len(ex);
@@ -2819,7 +2800,7 @@ ext4_ext_more_to_rm(struct ext4_ext_path *path)
 int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start,
 			  ext4_lblk_t end)
 {
-	struct super_block *sb = inode->i_sb;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	int depth = ext_depth(inode);
 	struct ext4_ext_path *path = NULL;
 	long long partial_cluster = 0;
@@ -2845,9 +2826,10 @@ again:
 	 */
 	if (end < EXT_MAX_BLOCKS - 1) {
 		struct ext4_extent *ex;
-		ext4_lblk_t ee_block;
+		ext4_lblk_t ee_block, ex_end, lblk;
+		ext4_fsblk_t pblk;
 
-		/* find extent for this block */
+		/* find extent for or closest extent to this block */
 		path = ext4_find_extent(inode, end, NULL, EXT4_EX_NOCACHE);
 		if (IS_ERR(path)) {
 			ext4_journal_stop(handle);
@@ -2867,6 +2849,7 @@ again:
 		}
 
 		ee_block = le32_to_cpu(ex->ee_block);
+		ex_end = ee_block + ext4_ext_get_actual_len(ex) - 1;
 
 		/*
 		 * See if the last block is inside the extent, if so split
@@ -2874,8 +2857,19 @@ again:
 		 * tail of the first part of the split extent in
 		 * ext4_ext_rm_leaf().
 		 */
-		if (end >= ee_block &&
-		    end < ee_block + ext4_ext_get_actual_len(ex) - 1) {
+		if (end >= ee_block && end < ex_end) {
+
+			/*
+			 * If we're going to split the extent, note that
+			 * the cluster containing the block after 'end' is
+			 * in use to avoid freeing it when removing blocks.
+			 */
+			if (sbi->s_cluster_ratio > 1) {
+				pblk = ext4_ext_pblock(ex) + end - ee_block + 2;
+				partial_cluster =
+					-(long long) EXT4_B2C(sbi, pblk);
+			}
+
 			/*
 			 * Split the extent in two so that 'end' is the last
 			 * block in the first new extent. Also we should not
@@ -2886,6 +2880,24 @@ again:
 							 end + 1, 1);
 			if (err < 0)
 				goto out;
+
+		} else if (sbi->s_cluster_ratio > 1 && end >= ex_end) {
+			/*
+			 * If there's an extent to the right its first cluster
+			 * contains the immediate right boundary of the
+			 * truncated/punched region.  Set partial_cluster to
+			 * its negative value so it won't be freed if shared
+			 * with the current extent.  The end < ee_block case
+			 * is handled in ext4_ext_rm_leaf().
+			 */
+			lblk = ex_end + 1;
+			err = ext4_ext_search_right(inode, path, &lblk, &pblk,
+						    &ex);
+			if (err)
+				goto out;
+			if (pblk)
+				partial_cluster =
+					-(long long) EXT4_B2C(sbi, pblk);
 		}
 	}
 	/*
@@ -3003,8 +3015,8 @@ again:
 		int flags = get_default_free_blocks_flags(inode);
 
 		ext4_free_blocks(handle, inode, NULL,
-				 EXT4_C2B(EXT4_SB(sb), partial_cluster),
-				 EXT4_SB(sb)->s_cluster_ratio, flags);
+				 EXT4_C2B(sbi, partial_cluster),
+				 sbi->s_cluster_ratio, flags);
 		partial_cluster = 0;
 	}