[Devel] [PATCH RHEL7 COMMIT] ext4: recalculate journal credits as inode depth changes

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1127.10.1.vz7.162.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.10.1.vz7.162.14
------>
commit d60645bc4da75817b1930921a907d69ef24ab95d
Author: Lukas Czerner <lczerner at redhat.com>
Date:   Sat Jul 25 09:21:46 2020 +0300

    ext4: recalculate journal credits as inode depth changes
    
    ms commit 4134f5c88dcd
    
    Currently in ext4_alloc_file_blocks() the number of credits is
    calculated only once before we enter the allocation loop. However within
    the allocation loop the extent tree depth can change, hence the number
    of credits needed can increase potentially exceeding the number of credits
    reserved in the handle which can cause journal failures.
    
    Fix this by recalculating number of credits when the inode depth
    changes. Note that even though ext4_alloc_file_blocks() is only
    currently used by extent base inodes we will avoid recalculating number
    of credits unnecessarily in the case of indirect based inodes.
    
    Signed-off-by: Lukas Czerner <lczerner at redhat.com>
    Signed-off-by: Theodore Ts'o <tytso at mit.edu>
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 fs/ext4/extents.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0a636ff128982..8d3e509f39b99 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4716,6 +4716,7 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
 	int ret = 0;
 	int ret2 = 0;
 	int retries = 0;
+	int depth = 0;
 	struct ext4_map_blocks map;
 	unsigned int credits;
 	loff_t epos;
@@ -4734,9 +4735,24 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
 	 * credits to insert 1 extent into extent tree
 	 */
 	credits = ext4_chunk_trans_blocks(inode, len);
+	/*
+	 * We can only call ext_depth() on extent based inodes
+	 */
+	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
+		depth = ext_depth(inode);
+	else
+		depth = -1;
 
 retry:
 	while (ret >= 0 && len) {
+		/*
+		 * Recalculate credits when extent tree depth changes.
+		 */
+		if (depth >= 0 && depth != ext_depth(inode)) {
+			credits = ext4_chunk_trans_blocks(inode, len);
+			depth = ext_depth(inode);
+		}
+
 		handle = ext4_journal_start(inode, EXT4_HT_MAP_BLOCKS,
 					    credits);
 		if (IS_ERR(handle)) {