ext4: gracefully handle ext4_break_layouts() failure during truncate

ext4_break_layouts() may fail e.g. due to a signal being delivered.
Thus we need to handle its failure gracefully and not by taking the
filesystem down. Currently ext4_break_layouts() failure is rare but it
may become more common once RDMA uses layout leases for handling
long-term page pins for DAX mappings.

To handle the failure we need to move ext4_break_layouts() earlier
during setattr handling before we do hard to undo changes such as
modifying inode size. To be able to do that we also have to move some
other checks which are better done without holding i_mmap_sem earlier.
Reported-and-tested-by: NIra Weiny <ira.weiny@intel.com>
Reviewed-by: NIra Weiny <ira.weiny@intel.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/ext4/inode.c

@@ -5571,7 +5571,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 	if (attr->ia_valid & ATTR_SIZE) {
 		handle_t *handle;
 		loff_t oldsize = inode->i_size;
-		int shrink = (attr->ia_size <= inode->i_size);
+		int shrink = (attr->ia_size < inode->i_size);
 
 		if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
 			struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
@@ -5585,18 +5585,33 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 		if (IS_I_VERSION(inode) && attr->ia_size != inode->i_size)
 			inode_inc_iversion(inode);
 
-		if (ext4_should_order_data(inode) &&
-		    (attr->ia_size < inode->i_size)) {
-			error = ext4_begin_ordered_truncate(inode,
+		if (shrink) {
+			if (ext4_should_order_data(inode)) {
+				error = ext4_begin_ordered_truncate(inode,
 							    attr->ia_size);
-			if (error)
-				goto err_out;
+				if (error)
+					goto err_out;
+			}
+			/*
+			 * Blocks are going to be removed from the inode. Wait
+			 * for dio in flight.
+			 */
+			inode_dio_wait(inode);
+		}
+
+		down_write(&EXT4_I(inode)->i_mmap_sem);
+
+		rc = ext4_break_layouts(inode);
+		if (rc) {
+			up_write(&EXT4_I(inode)->i_mmap_sem);
+			return rc;
 		}
+
 		if (attr->ia_size != inode->i_size) {
 			handle = ext4_journal_start(inode, EXT4_HT_INODE, 3);
 			if (IS_ERR(handle)) {
 				error = PTR_ERR(handle);
-				goto err_out;
+				goto out_mmap_sem;
 			}
 			if (ext4_handle_valid(handle) && shrink) {
 				error = ext4_orphan_add(handle, inode);
@@ -5624,42 +5639,31 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 				i_size_write(inode, attr->ia_size);
 			up_write(&EXT4_I(inode)->i_data_sem);
 			ext4_journal_stop(handle);
-			if (error) {
-				if (orphan && inode->i_nlink)
-					ext4_orphan_del(NULL, inode);
-				goto err_out;
+			if (error)
+				goto out_mmap_sem;
+			if (!shrink) {
+				pagecache_isize_extended(inode, oldsize,
+							 inode->i_size);
+			} else if (ext4_should_journal_data(inode)) {
+				ext4_wait_for_tail_page_commit(inode);
 			}
 		}
-		if (!shrink) {
-			pagecache_isize_extended(inode, oldsize, inode->i_size);
-		} else {
-			/*
-			 * Blocks are going to be removed from the inode. Wait
-			 * for dio in flight.
-			 */
-			inode_dio_wait(inode);
-		}
-		if (orphan && ext4_should_journal_data(inode))
-			ext4_wait_for_tail_page_commit(inode);
-		down_write(&EXT4_I(inode)->i_mmap_sem);
-
-		rc = ext4_break_layouts(inode);
-		if (rc) {
-			up_write(&EXT4_I(inode)->i_mmap_sem);
-			error = rc;
-			goto err_out;
-		}
 
 		/*
 		 * Truncate pagecache after we've waited for commit
 		 * in data=journal mode to make pages freeable.
 		 */
 		truncate_pagecache(inode, inode->i_size);
-		if (shrink) {
+		/*
+		 * Call ext4_truncate() even if i_size didn't change to
+		 * truncate possible preallocated blocks.
+		 */
+		if (attr->ia_size <= oldsize) {
 			rc = ext4_truncate(inode);
 			if (rc)
 				error = rc;
 		}
+out_mmap_sem:
 		up_write(&EXT4_I(inode)->i_mmap_sem);
 	}