From:   Harshad Shirwadkar <harshadshirwadkar@gmail.com>
To:     yinxin.x@bytedance.com
Cc:     adilger.kernel@dilger.ca, harshadshirwadkar@gmail.com,
        linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] ext4: fix fast commit may miss tracking range for FALLOC_FL_ZERO_RANGE
Date:   Fri, 17 Dec 2021 12:43:22 -0800
Message-Id: <20211217204322.1000035-1-harshads@google.com>
In-Reply-To: <20211201095258.1966-1-yinxin.x@bytedance.com>
References: <20211201095258.1966-1-yinxin.x@bytedance.com>
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> fs/ext4/extents.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>index 9229ab1f99c5..4108896d471b 100644
>--- a/fs/ext4/extents.c
>+++ b/fs/ext4/extents.c
>@@ -4433,6 +4433,8 @@ static int ext4_alloc_file_blocks(struct file *file, ext4_lblk_t offset,
> 			ret2 = ext4_journal_stop(handle);
> 			break;
> 		}
>+		ext4_fc_track_range(handle, inode, map.m_lblk,
>+					map.m_lblk + map.m_len - 1);

ext4_alloc_file_blocks() calls ext4_map_blocks(), inside which we do
call ext4_fc_track_range(). However, we are doing that only if
map.m_flags & EXT4_MAP_MAPPED is true. So, unwritten flag is set we
are not calling track_range there. Perhaps the right fix is to call
ext4_fc_track_range() from ext4_map_blocks() if MAPPED or UNWRITTEN
flag is set?

> 		map.m_lblk += ret;
> 		map.m_len = len = len - ret;
> 		epos = (loff_t)map.m_lblk << inode->i_blkbits;
>@@ -4599,8 +4601,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
> 	ret = ext4_mark_inode_dirty(handle, inode);
> 	if (unlikely(ret))
> 		goto out_handle;
>-	ext4_fc_track_range(handle, inode, offset >> inode->i_sb->s_blocksize_bits,
>-			(offset + len - 1) >> inode->i_sb->s_blocksize_bits);
> 	/* Zero out partial block at the edges of the range */
> 	ret = ext4_zero_partial_blocks(handle, inode, offset, len);
> 	if (ret >= 0)
>--