linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix to access i_size w/ i_size

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Message-ID: <45823945-2ea3-4ec6-9b07-686814f38567@kernel.org>
Date: Wed, 29 Oct 2025 17:41:22 +0800
From: Chao Yu <chao@...nel.org>
To: Yongpeng Yang <yangyongpeng.storage@...il.com>, jaegeuk@...nel.org
Cc: chao@...nel.org, linux-kernel@...r.kernel.org,
 linux-f2fs-devel@...ts.sourceforge.net,
 Yongpeng Yang <yangyongpeng@...omi.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix to access i_size w/ i_size_read()

On 10/29/25 16:09, Yongpeng Yang wrote:
> On 10/29/25 14:31, Chao Yu via Linux-f2fs-devel wrote:
>> It recommends to use i_size_{read,write}() to access and update i_size,
>> otherwise, we may get wrong tearing value due to high 32-bits value
>> and low 32-bits value of i_size field are not updated atomically in
>> 32-bits archicture machine.
>>
>> Signed-off-by: Chao Yu <chao@...nel.org>
>> ---
>>   include/trace/events/f2fs.h | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
>> index edbbd869078f..e1fae78d64a5 100644
>> --- a/include/trace/events/f2fs.h
>> +++ b/include/trace/events/f2fs.h
>> @@ -204,7 +204,7 @@ DECLARE_EVENT_CLASS(f2fs__inode,
>>           __entry->pino    = F2FS_I(inode)->i_pino;
>>           __entry->mode    = inode->i_mode;
>>           __entry->nlink    = inode->i_nlink;
>> -        __entry->size    = inode->i_size;
>> +        __entry->size    = i_size_read(inode);
>>           __entry->blocks    = inode->i_blocks;
>>           __entry->advise    = F2FS_I(inode)->i_advise;
>>       ),
>> @@ -353,7 +353,7 @@ TRACE_EVENT(f2fs_unlink_enter,
>>       TP_fast_assign(
>>           __entry->dev    = dir->i_sb->s_dev;
>>           __entry->ino    = dir->i_ino;
>> -        __entry->size    = dir->i_size;
>> +        __entry->size    = i_size_read(dir);
>>           __entry->blocks    = dir->i_blocks;
>>           __assign_str(name);
>>       ),
>> @@ -433,7 +433,7 @@ DECLARE_EVENT_CLASS(f2fs__truncate_op,
>>       TP_fast_assign(
>>           __entry->dev    = inode->i_sb->s_dev;
>>           __entry->ino    = inode->i_ino;
>> -        __entry->size    = inode->i_size;
>> +        __entry->size    = i_size_read(inode);
>>           __entry->blocks    = inode->i_blocks;
>>           __entry->from    = from;
>>       ),
>> @@ -1006,7 +1006,7 @@ TRACE_EVENT(f2fs_fallocate,
>>           __entry->mode    = mode;
>>           __entry->offset    = offset;
>>           __entry->len    = len;
>> -        __entry->size    = inode->i_size;
>> +        __entry->size    = i_size_read(inode);
>>           __entry->blocks = inode->i_blocks;
>>           __entry->ret    = ret;
>>       ),
> 
> inode->i_size usage in fs/f2fs/ also needs to be updated. For example in f2fs_need_verity(), which may not protected by inode_lock.

Accessing i_size directly in f2fs_need_verity() should be fine? Because fsverity
actived inode should be readonly.

Do you see any other cases which are not covered by inode_lock()?

Thanks,

> 
> Yongpeng,