linux-kernel - Re: [PATCH v4 10/12] ext4: make ext4_es_insert_delayed

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Message-ID: <20230610190319.GB1436857@mit.edu>
Date:   Sat, 10 Jun 2023 15:03:19 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     linux-ext4@...r.kernel.org, adilger.kernel@...ger.ca, jack@...e.cz,
        ritesh.list@...il.com, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v4 10/12] ext4: make ext4_es_insert_delayed_block()
 return void

On Mon, Apr 24, 2023 at 11:38:44AM +0800, Baokun Li wrote:
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index a0bfe77d5537..4221b2dafeb5 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1641,9 +1641,8 @@ static void ext4_print_free_blocks(struct inode *inode)
>  static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
>  {
>  	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> -	int ret;
> +	int ret = 0;
>  	bool allocated = false;
> -	bool reserved = false;
>  
>  	/*
>  	 * If the cluster containing lblk is shared with a delayed,

Unforuntately, the changes to ext4_insert_delayed_block() in this
patch were buggy, and were causing tests to hang when running
ext4/encrypt, ext4/bigalloc_4k, and ext4/bigalloc_1k test scenarios.
A bisect using "gce-xfstests -c ext4/bigalloc_4k -C 5 generic/579"
pinpointed the problem.

The problem is that ext4_clu_mapped can return a positive value, and
so there are times when we do need to release the space even though
there are no errors.

So I've fixed up your commit with the following changes.  With this
change, the test regressions go away.

Cheers,

						- Ted

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index fa38092ef868..3a10427240cb 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1630,6 +1630,7 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	int ret = 0;
 	bool allocated = false;
+	bool reserved = false;
 
 	/*
 	 * If the cluster containing lblk is shared with a delayed,
@@ -1646,6 +1647,7 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
 		ret = ext4_da_reserve_space(inode);
 		if (ret != 0)   /* ENOSPC */
 			goto errout;
+		reserved = true;
 	} else {   /* bigalloc */
 		if (!ext4_es_scan_clu(inode, &ext4_es_is_delonly, lblk)) {
 			if (!ext4_es_scan_clu(inode,
@@ -1658,6 +1660,7 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
 					ret = ext4_da_reserve_space(inode);
 					if (ret != 0)   /* ENOSPC */
 						goto errout;
+					reserved = true;
 				} else {
 					allocated = true;
 				}
@@ -1668,6 +1671,9 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
 	}
 
 	ext4_es_insert_delayed_block(inode, lblk, allocated);
+	if (ret && reserved)
+		ext4_da_release_space(inode, 1);
+
 errout:
 	return ret;
 }