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SubjectRe: [PATCH v3] f2fs: Reduce the scope of setting fsck tag when de->name_len is zero
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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 '^'

> 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 <frank.li@vivo.com>
> ---
> 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;

Thanks,

> int err = 0;
>
> bit_pos = ((unsigned long)ctx->pos % d->max);
> @@ -1014,13 +1015,15 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
>
> de = &d->dentry[bit_pos];
> if (de->name_len == 0) {
> + if (found_valid_dirent || !bit_pos) {
> + printk_ratelimited(
> + "%sF2FS-fs (%s): invalid namelen(0), ino:%u, run fsck to fix.",
> + KERN_WARNING, sbi->sb->s_id,
> + le32_to_cpu(de->ino));
> + set_sbi_flag(sbi, SBI_NEED_FSCK);
> + }
> bit_pos++;
> ctx->pos = start_pos + bit_pos;
> - printk_ratelimited(
> - "%sF2FS-fs (%s): invalid namelen(0), ino:%u, run fsck to fix.",
> - KERN_WARNING, sbi->sb->s_id,
> - le32_to_cpu(de->ino));
> - set_sbi_flag(sbi, SBI_NEED_FSCK);
> continue;
> }
>
> @@ -1063,6 +1066,7 @@ int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
> f2fs_ra_node_page(sbi, le32_to_cpu(de->ino));
>
> ctx->pos = start_pos + bit_pos;
> + found_valid_dirent = true;
> }
> out:
> if (readdir_ra)
>

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