[PATCH v2] ext4: Gracefully handle ext4_break_layouts() failure during truncate

[PATCH v2] ext4: Gracefully handle ext4_break_layouts() failure during truncate

[Jan Kara]

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: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/inode.c | 66 ++++++++++++++++++++++++++++++---------------------------
 1 file changed, 35 insertions(+), 31 deletions(-)

A version of the fix that passes also generic/092 test.

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c7f77c643008..c16071547c9c 100644
--- a/fs/ext4/inode.c
+++ b/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);
 	}
 
-- 
2.16.4

Re: [PATCH v2] ext4: Gracefully handle ext4_break_layouts() failure during truncate

[Theodore Ts'o]

On Tue, May 28, 2019 at 10:05:45AM +0200, Jan Kara wrote:
> 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: Ira Weiny <ira.weiny@intel.com>
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Jan Kara <jack@suse.cz>

Applied, thanks!

					- Ted