Re:Re: [PATCH v3] f2fs: Reduce the scope of setting fsck tag when de->name_len is zero
Date: Tue Jul 20 2021 - 08:32:06 EST
From: Chao Yu <chao@xxxxxxxxxx>
Date: 2021-07-20 18:23:15
To: Yangtao Li <frank.li@xxxxxxxx>,jaegeuk@xxxxxxxxxx
Subject: Re: [PATCH v3] f2fs: Reduce the scope of setting fsck tag when de->name_len is zero>On 2021/7/20 15:06, Yangtao Li wrote:
>> I recently found a case where de->name_len is 0 in f2fs_fill_dentries() easily reproduced,
>> and finally set the fsck flag.
>> Thread A Thread B
>> ctx->pos = d.max
>> set_sbi_flag(sbi, SBI_NEED_FSCK)
>> Process A opens the folder, and has been reading without closing it. During this period,
>> Process B created a file under the folder (occupying multiple f2fs_dir_entry, exceeding
>> the d.max of the inline dir). After creation, process A uses the d.max of inline dir to
>> read it again, and it will read that de->name_len is 0.
>> And Chao pointed out that w/o inline conversion, the race condition still can happen as below
>> dir_entry1: A
>> dir_entry2: B
>> dir_entry3: C
>> free slot: _
>> ctx->pos: ^
>please use blank instead of tab before '^'
I don't know exactly what happened. In fact, in v2, spaces were used. Then it was changed to tab in v3.
>> Thread B delete dir_entry2, and create dir_entry3.
>> In these scenarios, the file system is not damaged, and it's hard to avoid it. But we can bypass
>> tagging FSCK flag if:
>> a) bit_pos (:= ctx->pos % d->max) is non-zero & b) before bit_pos moves to first
>> valid dir_entry.
>> Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>
>> fs/f2fs/dir.c | 14 +++++++++-----
>> 1 file changed, 9 insertions(+), 5 deletions(-)
>> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
>> index 456651682daf..bfe942733b5e 100644
>> --- a/fs/f2fs/dir.c
>> +++ b/fs/f2fs/dir.c
>> @@ -1000,6 +1000,7 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
>> struct f2fs_sb_info *sbi = F2FS_I_SB(d->inode);
>> struct blk_plug plug;
>> bool readdir_ra = sbi->readdir_ra == 1;
>> + bool found_valid_dirent = false;
>One more blank before '='.
>bool found_valid_dirent = false;