HI Chao， From: Chao Yu <[email protected]> Date: 2021-07-20 18:23:15 To: Yangtao Li <[email protected]>,[email protected] Cc: [email protected],[email protected] 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 >> >> f2fs_readdir >> f2fs_read_inline_dir >> ctx->pos = d.max >> f2fs_add_dentry >> f2fs_add_inline_entry >> >> do_convert_inline_dir >> f2fs_add_regular_entry >> f2fs_readdir >> f2fs_fill_dentries >> 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: ^ >> >> Before: >> AAAABBBB___ >> ^ > >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. >> >> After: >> AAAACCCCC__ >> ^ > >Ditto > >> >> 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 <[email protected]> >> --- >> 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; > OK. Thx， _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
