Re: [PATCH v3] f2fs: Introduce linear search for dentries

From: Jaegeuk Kim
Date: Mon Dec 23 2024 - 12:14:48 EST

On 12/22, Chao Yu wrote:
> On 2024/12/21 7:41, Daniel Lee wrote:
> > This patch addresses an issue where some files in case-insensitive
> > directories become inaccessible due to changes in how the kernel function,
> > utf8_casefold(), generates case-folded strings from the commit 5c26d2f1d3f5
> > ("unicode: Don't special case ignorable code points").
> >
> > F2FS uses these case-folded names to calculate hash values for locating
> > dentries and stores them on disk. Since utf8_casefold() can produce
> > different output across kernel versions, stored hash values and newly
> > calculated hash values may differ. This results in affected files no
> > longer being found via the hash-based lookup.
> >
> > To resolve this, the patch introduces a linear search fallback.
> > If the initial hash-based search fails, F2FS will sequentially scan the
> > directory entries.
> >
> > Fixes: 5c26d2f1d3f5 ("unicode: Don't special case ignorable code points")
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=219586
> > Signed-off-by: Daniel Lee <chullee@xxxxxxxxxx>
> > ---
> > v3:
> > - Fix the unused label warning
> > v2:
> > - Only update chash if use_hash is true
> > fs/f2fs/dir.c | 42 +++++++++++++++++++++++++++++++-----------
> > fs/f2fs/f2fs.h | 6 ++++--
> > fs/f2fs/inline.c | 5 +++--
> > 3 files changed, 38 insertions(+), 15 deletions(-)
> >
> > diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> > index 47a5c806cf16..058b8be9a373 100644
> > --- a/fs/f2fs/dir.c
> > +++ b/fs/f2fs/dir.c
> > @@ -175,7 +175,8 @@ static unsigned long dir_block_index(unsigned int level,
> > static struct f2fs_dir_entry *find_in_block(struct inode *dir,
> > struct page *dentry_page,
> > const struct f2fs_filename *fname,
> > - int *max_slots)
> > + int *max_slots,
> > + bool use_hash)
> > {
> > struct f2fs_dentry_block *dentry_blk;
> > struct f2fs_dentry_ptr d;
> > @@ -183,7 +184,7 @@ static struct f2fs_dir_entry *find_in_block(struct inode *dir,
> > dentry_blk = (struct f2fs_dentry_block *)page_address(dentry_page);
> > make_dentry_ptr_block(dir, &d, dentry_blk);
> > - return f2fs_find_target_dentry(&d, fname, max_slots);
> > + return f2fs_find_target_dentry(&d, fname, max_slots, use_hash);
> > }
> > static inline int f2fs_match_name(const struct inode *dir,
> > @@ -208,7 +209,8 @@ static inline int f2fs_match_name(const struct inode *dir,
> > }
> > struct f2fs_dir_entry *f2fs_find_target_dentry(const struct f2fs_dentry_ptr *d,
> > - const struct f2fs_filename *fname, int *max_slots)
> > + const struct f2fs_filename *fname, int *max_slots,
> > + bool use_hash)
> > {
> > struct f2fs_dir_entry *de;
> > unsigned long bit_pos = 0;
> > @@ -231,7 +233,7 @@ struct f2fs_dir_entry *f2fs_find_target_dentry(const struct f2fs_dentry_ptr *d,
> > continue;
> > }
> > - if (de->hash_code == fname->hash) {
> > + if (!use_hash || de->hash_code == fname->hash) {
> > res = f2fs_match_name(d->inode, fname,
> > d->filename[bit_pos],
> > le16_to_cpu(de->name_len));
> > @@ -258,11 +260,12 @@ struct f2fs_dir_entry *f2fs_find_target_dentry(const struct f2fs_dentry_ptr *d,
> > static struct f2fs_dir_entry *find_in_level(struct inode *dir,
> > unsigned int level,
> > const struct f2fs_filename *fname,
> > - struct page **res_page)
> > + struct page **res_page,
> > + bool use_hash)
> > {
> > int s = GET_DENTRY_SLOTS(fname->disk_name.len);
> > unsigned int nbucket, nblock;
> > - unsigned int bidx, end_block;
> > + unsigned int bidx, end_block, bucket_no;
> > struct page *dentry_page;
> > struct f2fs_dir_entry *de = NULL;
> > pgoff_t next_pgofs;
> > @@ -272,8 +275,11 @@ static struct f2fs_dir_entry *find_in_level(struct inode *dir,
> > nbucket = dir_buckets(level, F2FS_I(dir)->i_dir_level);
> > nblock = bucket_blocks(level);
> > + bucket_no = use_hash ? le32_to_cpu(fname->hash) % nbucket : 0;
> > +
> > +start_find_bucket:
> > bidx = dir_block_index(level, F2FS_I(dir)->i_dir_level,
> > - le32_to_cpu(fname->hash) % nbucket);
> > + bucket_no);
> > end_block = bidx + nblock;
> > while (bidx < end_block) {
> > @@ -290,7 +296,7 @@ static struct f2fs_dir_entry *find_in_level(struct inode *dir,
> > }
> > }
> > - de = find_in_block(dir, dentry_page, fname, &max_slots);
> > + de = find_in_block(dir, dentry_page, fname, &max_slots, use_hash);
> > if (IS_ERR(de)) {
> > *res_page = ERR_CAST(de);
> > de = NULL;
> > @@ -307,7 +313,10 @@ static struct f2fs_dir_entry *find_in_level(struct inode *dir,
> > bidx++;
> > }
> > - if (!de && room && F2FS_I(dir)->chash != fname->hash) {
> > + if (!use_hash && !de && ++bucket_no < nbucket)
> > + goto start_find_bucket;
> > +
> > + if (use_hash && !de && room && F2FS_I(dir)->chash != fname->hash) {
> > F2FS_I(dir)->chash = fname->hash;
> > F2FS_I(dir)->clevel = level;
>
> What about cleaning up w/
>
> if (de)
> return de;
>
> if (use_hash) {

Applied w/
if (likely(use_hash)) {

Thanks,

> if (room && F2FS_I(dir)->chash != fname->hash) {
> ...
> }
> } else if (++bucket_no < nbucket)
> goto start_find_bucket;
> }
> return NULL;
>
> Otherwise, it looks good to me, anyway,
>
> Reviewed-by: Chao Yu <chao@xxxxxxxxxx>
>
> Thanks,
>
> > }
> > @@ -323,11 +332,15 @@ struct f2fs_dir_entry *__f2fs_find_entry(struct inode *dir,
> > struct f2fs_dir_entry *de = NULL;
> > unsigned int max_depth;
> > unsigned int level;
> > + bool use_hash = true;
> > *res_page = NULL;
> > +#if IS_ENABLED(CONFIG_UNICODE)
> > +start_find_entry:
> > +#endif
> > if (f2fs_has_inline_dentry(dir)) {
> > - de = f2fs_find_in_inline_dir(dir, fname, res_page);
> > + de = f2fs_find_in_inline_dir(dir, fname, res_page, use_hash);
> > goto out;
> > }
> > @@ -343,11 +356,18 @@ struct f2fs_dir_entry *__f2fs_find_entry(struct inode *dir,
> > }
> > for (level = 0; level < max_depth; level++) {
> > - de = find_in_level(dir, level, fname, res_page);
> > + de = find_in_level(dir, level, fname, res_page, use_hash);
> > if (de || IS_ERR(*res_page))
> > break;
> > }
> > +
> > out:
> > +#if IS_ENABLED(CONFIG_UNICODE)
> > + if (IS_CASEFOLDED(dir) && !de && use_hash) {
> > + use_hash = false;
> > + goto start_find_entry;
> > + }
> > +#endif
> > /* This is to increase the speed of f2fs_create */
> > if (!de)
> > F2FS_I(dir)->task = current;
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index f523dd302bf6..1afebb9c4061 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -3588,7 +3588,8 @@ int f2fs_prepare_lookup(struct inode *dir, struct dentry *dentry,
> > struct f2fs_filename *fname);
> > void f2fs_free_filename(struct f2fs_filename *fname);
> > struct f2fs_dir_entry *f2fs_find_target_dentry(const struct f2fs_dentry_ptr *d,
> > - const struct f2fs_filename *fname, int *max_slots);
> > + const struct f2fs_filename *fname, int *max_slots,
> > + bool use_hash);
> > int f2fs_fill_dentries(struct dir_context *ctx, struct f2fs_dentry_ptr *d,
> > unsigned int start_pos, struct fscrypt_str *fstr);
> > void f2fs_do_make_empty_dir(struct inode *inode, struct inode *parent,
> > @@ -4224,7 +4225,8 @@ int f2fs_write_inline_data(struct inode *inode, struct folio *folio);
> > int f2fs_recover_inline_data(struct inode *inode, struct page *npage);
> > struct f2fs_dir_entry *f2fs_find_in_inline_dir(struct inode *dir,
> > const struct f2fs_filename *fname,
> > - struct page **res_page);
> > + struct page **res_page,
> > + bool use_hash);
> > int f2fs_make_empty_inline_dir(struct inode *inode, struct inode *parent,
> > struct page *ipage);
> > int f2fs_add_inline_entry(struct inode *dir, const struct f2fs_filename *fname,
> > diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
> > index cbd2a0d34804..3e3c35d4c98b 100644
> > --- a/fs/f2fs/inline.c
> > +++ b/fs/f2fs/inline.c
> > @@ -352,7 +352,8 @@ int f2fs_recover_inline_data(struct inode *inode, struct page *npage)
> > struct f2fs_dir_entry *f2fs_find_in_inline_dir(struct inode *dir,
> > const struct f2fs_filename *fname,
> > - struct page **res_page)
> > + struct page **res_page,
> > + bool use_hash)
> > {
> > struct f2fs_sb_info *sbi = F2FS_SB(dir->i_sb);
> > struct f2fs_dir_entry *de;
> > @@ -369,7 +370,7 @@ struct f2fs_dir_entry *f2fs_find_in_inline_dir(struct inode *dir,
> > inline_dentry = inline_data_addr(dir, ipage);
> > make_dentry_ptr_inline(dir, &d, inline_dentry);
> > - de = f2fs_find_target_dentry(&d, fname, NULL);
> > + de = f2fs_find_target_dentry(&d, fname, NULL, use_hash);
> > unlock_page(ipage);
> > if (IS_ERR(de)) {
> > *res_page = ERR_CAST(de);