Re: [f2fs-dev] [PATCH] f2fs: fix to zero post-EOF data when extending file size

[Chao Yu <chao@kernel.org>]

On 7/16/26 02:05, Jaegeuk Kim wrote:
> This causes sysmtem hang during xfstests.

Fixed a potential deadlock issue during checkpoint in v2, though I can
not reproduce it.

Thanks,

> 
> On 07/06, Chao Yu via Linux-f2fs-devel wrote:
>> generic/794  4s ... - output mismatch (see /share/git/fstests/results//generic/794.out.bad)
>>      --- tests/generic/794.out   2026-06-12 08:46:32.766426241 +0800
>>      +++ /share/git/fstests/results//generic/794.out.bad 2026-07-05 18:32:55.000000000 +0800
>>      @@ -1,4 +1,16 @@
>>       QA output created by 794
>>       append_write
>>      +FAIL: non-zero data in gap [4080,4096) after shutdown+remount
>>      +000000 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a  >ZZZZZZZZZZZZZZZZ<
>>      +*
>>      +001000
>>       truncate_up
>>      ...
>>      (Run 'diff -u /share/git/fstests/tests/generic/794.out /share/git/fstests/results//generic/794.out.bad'  to see the entire diff)
>> Ran: generic/794
>> Failures: generic/794
>> Failed 1 of 1 tests
>>
>> Steps of generic/794:
>> 1. write 4096 bytes to file w/ 0x5a
>> 2. use fiemap to get PBA of first block in file
>> 3. truncate file to 4080
>> 4. umount; write 4096 bytes to file w/ 0x5a directly via PBA; mount
>> 5. extend filesize via
>>     a) append 4096 from offset 4096, or
>>     b) truncate 8192, or
>>     c) fallocate 4096 from offset 4096
>> 6. verify the gap is zeroed in memory [4080,4096)
>> 7. sync range 4096 from offset 4096; shutdown -f (flush meta before shutdown)
>> 8. umount; mount; verify [4080,4096) is zeroed or not.
>>
>> When extending file size (e.g. via truncate, fallocate, or write) across an
>> unaligned EOF boundary, we need to ensure that post-EOF data in the partial
>> page is zeroed out in pagecache and marked dirty, meanwhile, tagging the inode
>> with FI_ZERO_POST_EOF, so that following checkpoint() and fsync() can persist
>> the page contain zeroed data before committing inode w/ updated i_size.
>>
>> This help to prevent stale disk data beyond the previous EOF from being exposed
>> after remounting or crash recovery.
>>
>> Since f2fs is a LFS filesystem, we only support direct write via PBA in pinfile,
>> and pinfile has section-aligned filesize, so in Android, there should no problem,
>> but for other usage in different environment, let's fix this w/ fsync_mode=strict
>> mount option.
>>
>> Cc: stable@kernel.org
>> Signed-off-by: Chao Yu <chao@kernel.org>
>> ---
>>   fs/f2fs/checkpoint.c |  4 ++++
>>   fs/f2fs/f2fs.h       |  1 +
>>   fs/f2fs/file.c       | 35 ++++++++++++++++++++++++++++++++---
>>   3 files changed, 37 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>> index 064f5b537423..6f486d3a94c7 100644
>> --- a/fs/f2fs/checkpoint.c
>> +++ b/fs/f2fs/checkpoint.c
>> @@ -1359,6 +1359,10 @@ static int f2fs_sync_inode_meta(struct f2fs_sb_info *sbi)
>>   		inode = igrab(&fi->vfs_inode);
>>   		spin_unlock(&sbi->inode_lock[DIRTY_META]);
>>   		if (inode) {
>> +			if (is_inode_flag_set(inode, FI_ZERO_POST_EOF)) {
>> +				filemap_write_and_wait(inode->i_mapping);
>> +				clear_inode_flag(inode, FI_ZERO_POST_EOF);
>> +			}
>>   			sync_inode_metadata(inode, 0);
>>   
>>   			/* it's on eviction */
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 8e2fb0bda467..41be09dad43c 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -939,6 +939,7 @@ enum {
>>   	FI_ATOMIC_REPLACE,	/* indicate atomic replace */
>>   	FI_OPENED_FILE,		/* indicate file has been opened */
>>   	FI_DONATE_FINISHED,	/* indicate page donation of file has been finished */
>> +	FI_ZERO_POST_EOF,	/* indicate unaligned EOF gap was zeroed in pagecache */
>>   	FI_MAX,			/* max flag, never be used */
>>   };
>>   
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 11cc8d79c235..2e9d585073ec 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -36,21 +36,43 @@
>>   #include <trace/events/f2fs.h>
>>   #include <uapi/linux/f2fs.h>
>>   
>> +static int fill_zero(struct inode *inode, pgoff_t index,
>> +					loff_t start, loff_t len);
>> +
>>   static void f2fs_zero_post_eof_page(struct inode *inode,
>>   					loff_t new_size, bool lock)
>>   {
>>   	loff_t old_size = i_size_read(inode);
>> +	unsigned int offset;
>>   
>>   	if (old_size >= new_size)
>>   		return;
>>   
>> -	if (mapping_empty(inode->i_mapping))
>> -		return;
>> -
>>   	if (lock)
>>   		filemap_invalidate_lock(inode->i_mapping);
>> +
>>   	/* zero or drop pages only in range of [old_size, new_size] */
>>   	truncate_inode_pages_range(inode->i_mapping, old_size, new_size);
>> +
>> +	/*
>> +	 * When expanding an unaligned EOF size, zero post-EOF data in
>> +	 * pagecache and set FI_ZERO_POST_EOF, so following checkpointing
>> +	 * or fsync can persist correct data to disk before committing
>> +	 * inode w/ updated i_size.
>> +	 */
>> +	if (F2FS_OPTION(F2FS_I_SB(inode)).fsync_mode != FSYNC_MODE_STRICT)
>> +		goto out_unlock;
>> +
>> +	offset = old_size & (PAGE_SIZE - 1);
>> +	if (offset) {
>> +		unsigned int len = min_t(loff_t, PAGE_SIZE - offset,
>> +							new_size - old_size);
>> +		pgoff_t index = old_size >> PAGE_SHIFT;
>> +
>> +		fill_zero(inode, index, offset, len);
>> +		set_inode_flag(inode, FI_ZERO_POST_EOF);
>> +	}
>> +out_unlock:
>>   	if (lock)
>>   		filemap_invalidate_unlock(inode->i_mapping);
>>   }
>> @@ -304,6 +326,13 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>>   	if (S_ISDIR(inode->i_mode))
>>   		goto go_write;
>>   
>> +	if (is_inode_flag_set(inode, FI_ZERO_POST_EOF)) {
>> +		ret = filemap_write_and_wait(inode->i_mapping);
>> +		if (ret)
>> +			return ret;
>> +		clear_inode_flag(inode, FI_ZERO_POST_EOF);
>> +	}
>> +
>>   	/* if fdatasync is triggered, let's do in-place-update */
>>   	if (datasync || get_dirty_pages(inode) <= SM_I(sbi)->min_fsync_blocks)
>>   		set_inode_flag(inode, FI_NEED_IPU);
>> -- 
>> 2.49.0
>>
>>
>>
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