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Message-ID: <Y4E++JERgUMoqfjG@ZenIV>
Date: Fri, 25 Nov 2022 22:17:28 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc: Evgeniy Dushistov <dushistov@...l.ru>,
Christian Brauner <brauner@...nel.org>,
linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
"Venkataramanan, Anirudh" <anirudh.venkataramanan@...el.com>,
Ira Weiny <ira.weiny@...el.com>
Subject: Re: [RESEND PATCH v4] fs/ufs: Replace kmap() with kmap_local_page()
On Sun, Oct 16, 2022 at 06:38:55PM +0200, Fabio M. De Francesco wrote:
> kmap() is being deprecated in favor of kmap_local_page().
Umm... I'm not sure it's the right way to handle that. Look:
> -static inline void ufs_put_page(struct page *page)
> +inline void ufs_put_page(struct page *page, void *page_addr)
> {
> - kunmap(page);
> + kunmap_local(page_addr);
Make that
kunmap_local((void *)((unsigned long)page_addr & PAGE_MASK));
and things become much easier.
> put_page(page);
> }
>
> @@ -72,11 +72,12 @@ ino_t ufs_inode_by_name(struct inode *dir, const struct qstr *qstr)
> if (de) {
> res = fs32_to_cpu(dir->i_sb, de->d_ino);
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
ufs_put_page(page, de);
and page_addr is not needed.
> /* Releases the page */
> void ufs_set_link(struct inode *dir, struct ufs_dir_entry *de,
> - struct page *page, struct inode *inode,
> - bool update_times)
> + struct page *page, void *page_addr,
> + struct inode *inode, bool update_times)
> {
> loff_t pos = page_offset(page) +
> - (char *) de - (char *) page_address(page);
> + (char *)de - (char *)page_addr;
loff_t pos = page_offset(page) + offset_in_page(de);
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
ufs_put_page(page, de);
and page_addr is unused, i.e. caller of ufs_set_link() don't need
any changes at all.
> +static struct page *ufs_get_page(struct inode *dir, unsigned long n, void **page_addr)
I suspect that
static void *ufs_get_page(struct inode *dir, unsigned long n, struct page **page)
would be better for callers.
> -struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p)
> +/*
> + * Return the '..' directory entry and the page in which the entry was found
> + * (as a parameter - p).
> + *
> + * On Success ufs_put_page() should be called on *p.
> + *
> + * NOTE: Calls to ufs_get_page()/ufs_put_page() must be nested according to
> + * the rules documented in kmap_local_page()/kunmap_local().
> + *
> + * ufs_find_entry() and ufs_dotdot() act as calls to ufs_get_page() and
> + * must be treated accordingly for nesting purposes.
> + */
> +struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **p, void **pa)
> {
> - struct page *page = ufs_get_page(dir, 0);
> + void *page_addr;
> + struct page *page = ufs_get_page(dir, 0, &page_addr);
> struct ufs_dir_entry *de = NULL;
>
> if (!IS_ERR(page)) {
> de = ufs_next_entry(dir->i_sb,
> - (struct ufs_dir_entry *)page_address(page));
> + (struct ufs_dir_entry *)page_addr);
> *p = page;
> + *pa = page_addr;
Callers can reconstruct page_addr by de. The function itself becomes
struct ufs_dir_entry *ufs_dotdot(struct inode *dir, struct page **page)
{
struct ufs_dir_entry *de = ufs_get_page(dir, 0, page);
if (!IS_ERR(de))
return ufs_next_entry(dir->i_sb, de);
else
return NULL;
}
and callers need no changes at all.
> struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> - struct page **res_page)
> + struct page **res_page, void **res_page_addr)
Same story; *res_page_addr is rounded return value.
> @@ -275,9 +306,10 @@ struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> n = start;
> do {
> char *kaddr;
> - page = ufs_get_page(dir, n);
> +
> + page = ufs_get_page(dir, n, &page_addr);
> if (!IS_ERR(page)) {
> - kaddr = page_address(page);
> + kaddr = page_addr;
char *kaddr = ufs_get_page(dir, n, &page);
if (!IS_ERR(kaddr) {
> de = (struct ufs_dir_entry *) kaddr;
> kaddr += ufs_last_byte(dir, n) - reclen;
> while ((char *) de <= kaddr) {
> @@ -285,7 +317,7 @@ struct ufs_dir_entry *ufs_find_entry(struct inode *dir, const struct qstr *qstr,
> goto found;
> de = ufs_next_entry(sb, de);
> }
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
ufs_put_page(page, kaddr);
it's in the same page...
> @@ -312,6 +345,7 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> const unsigned int chunk_size = UFS_SB(sb)->s_uspi->s_dirblksize;
> unsigned short rec_len, name_len;
> struct page *page = NULL;
> + void *page_addr = NULL;
> struct ufs_dir_entry *de;
> unsigned long npages = dir_pages(dir);
> unsigned long n;
> @@ -329,12 +363,12 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> for (n = 0; n <= npages; n++) {
> char *dir_end;
>
> - page = ufs_get_page(dir, n);
> + page = ufs_get_page(dir, n, &page_addr);
> err = PTR_ERR(page);
> if (IS_ERR(page))
> goto out;
> lock_page(page);
> - kaddr = page_address(page);
> + kaddr = page_addr;
kaddr = ufs_get_page(dir, n, &page);
err = PTR_ERR(kaddr);
if (IS_ERR(kaddr))
goto out;
lock_page(page);
> dir_end = kaddr + ufs_last_byte(dir, n);
> de = (struct ufs_dir_entry *)kaddr;
> kaddr += PAGE_SIZE - reclen;
> @@ -365,14 +399,14 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> de = (struct ufs_dir_entry *) ((char *) de + rec_len);
> }
> unlock_page(page);
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
ufs_put_page(page, kaddr);
> }
> BUG();
> return -EINVAL;
>
> got_it:
> pos = page_offset(page) +
> - (char*)de - (char*)page_address(page);
> + (char *)de - (char *)page_addr;
pos = page_offset(page) + offset_in_page(de);
> err = ufs_prepare_chunk(page, pos, rec_len);
> if (err)
> goto out_unlock;
> @@ -396,7 +430,7 @@ int ufs_add_link(struct dentry *dentry, struct inode *inode)
> mark_inode_dirty(dir);
> /* OFFSET_CACHE */
> out_put:
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
ufs_put_page(page, kaddr);
> out:
> return err;
> out_unlock:
> @@ -441,7 +475,7 @@ ufs_readdir(struct file *file, struct dir_context *ctx)
> char *kaddr, *limit;
> struct ufs_dir_entry *de;
>
> - struct page *page = ufs_get_page(inode, n);
> + struct page *page = ufs_get_page(inode, n, (void **)&kaddr);
Yecch...
kaddr = ufs_get_page(inode, n, &page);
with obvious change of error check below. It definitely looks like
more convenient calling conventions - getting rid of casts like that...
> int ufs_delete_entry(struct inode *inode, struct ufs_dir_entry *dir,
> - struct page * page)
> + struct page *page, char *kaddr)
Do we need it? If not, ufs_delete_entry() calls need no changes...
> {
> struct super_block *sb = inode->i_sb;
> - char *kaddr = page_address(page);
> unsigned from = ((char*)dir - kaddr) & ~(UFS_SB(sb)->s_uspi->s_dirblksize - 1);
> unsigned to = ((char*)dir - kaddr) + fs16_to_cpu(sb, dir->d_reclen);
> loff_t pos;
umm...
kaddr = (char *)((unsigned long)dir & PAGE_MASK);
unsigned from = offset_in_page(dir) & ....
unsigned to = offset_in_page(dir) + ....
> @@ -522,7 +554,7 @@ int ufs_delete_entry(struct inode *inode, struct ufs_dir_entry *dir,
> de = ufs_next_entry(sb, de);
> }
> if (pde)
> - from = (char*)pde - (char*)page_address(page);
> + from = (char *)pde - kaddr;
Note that this is
from = offset_in_page(pde);
> out:
> - ufs_put_page(page);
> + ufs_put_page(page, kaddr);
> UFSD("EXIT\n");
> return err;
> }
> @@ -592,17 +623,18 @@ int ufs_empty_dir(struct inode * inode)
> {
> struct super_block *sb = inode->i_sb;
> struct page *page = NULL;
> + void *page_addr;
> unsigned long i, npages = dir_pages(inode);
>
> for (i = 0; i < npages; i++) {
> char *kaddr;
> struct ufs_dir_entry *de;
> - page = ufs_get_page(inode, i);
>
> + page = ufs_get_page(inode, i, &page_addr);
> if (IS_ERR(page))
> continue;
>
> - kaddr = page_address(page);
> + kaddr = page_addr;
kaddr = ufs_get_page(inode, i, &page);
if (IS_ERR(kaddr))
continue;
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
ufs_put_page(page, kaddr)
> }
> return 1;
>
> not_empty:
> - ufs_put_page(page);
> + ufs_put_page(page, page_addr);
same here.
> return 0;
> }
>
> diff --git a/fs/ufs/namei.c b/fs/ufs/namei.c
> index 29d5a0e0c8f0..cdf3bcf9d02e 100644
> --- a/fs/ufs/namei.c
> +++ b/fs/ufs/namei.c
> @@ -210,13 +210,14 @@ static int ufs_unlink(struct inode *dir, struct dentry *dentry)
> struct inode * inode = d_inode(dentry);
> struct ufs_dir_entry *de;
> struct page *page;
> + void *page_addr;
> int err = -ENOENT;
>
> - de = ufs_find_entry(dir, &dentry->d_name, &page);
> + de = ufs_find_entry(dir, &dentry->d_name, &page, &page_addr);
> if (!de)
> goto out;
>
> - err = ufs_delete_entry(dir, de, page);
> + err = ufs_delete_entry(dir, de, page, page_addr);
> if (err)
> goto out;
None of that is needed.
> @@ -250,27 +251,31 @@ static int ufs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> struct inode *old_inode = d_inode(old_dentry);
> struct inode *new_inode = d_inode(new_dentry);
> struct page *dir_page = NULL;
> + void *dir_page_addr;
> struct ufs_dir_entry * dir_de = NULL;
> struct page *old_page;
> + void *old_page_addr;
> struct ufs_dir_entry *old_de;
> int err = -ENOENT;
>
> if (flags & ~RENAME_NOREPLACE)
> return -EINVAL;
>
> - old_de = ufs_find_entry(old_dir, &old_dentry->d_name, &old_page);
> + old_de = ufs_find_entry(old_dir, &old_dentry->d_name, &old_page,
> + &old_page_addr);
> if (!old_de)
> goto out;
>
> if (S_ISDIR(old_inode->i_mode)) {
> err = -EIO;
> - dir_de = ufs_dotdot(old_inode, &dir_page);
> + dir_de = ufs_dotdot(old_inode, &dir_page, &dir_page_addr);
> if (!dir_de)
> goto out_old;
> }
>
> if (new_inode) {
> struct page *new_page;
> + void *new_page_addr;
> struct ufs_dir_entry *new_de;
>
> err = -ENOTEMPTY;
> @@ -278,10 +283,11 @@ static int ufs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> goto out_dir;
>
> err = -ENOENT;
> - new_de = ufs_find_entry(new_dir, &new_dentry->d_name, &new_page);
> + new_de = ufs_find_entry(new_dir, &new_dentry->d_name, &new_page,
> + &new_page_addr);
> if (!new_de)
> goto out_dir;
> - ufs_set_link(new_dir, new_de, new_page, old_inode, 1);
> + ufs_set_link(new_dir, new_de, new_page, new_page_addr, old_inode, 1);
> new_inode->i_ctime = current_time(new_inode);
> if (dir_de)
> drop_nlink(new_inode);
> @@ -300,29 +306,25 @@ static int ufs_rename(struct user_namespace *mnt_userns, struct inode *old_dir,
> */
> old_inode->i_ctime = current_time(old_inode);
>
> - ufs_delete_entry(old_dir, old_de, old_page);
> + ufs_delete_entry(old_dir, old_de, old_page, old_page_addr);
> mark_inode_dirty(old_inode);
>
> if (dir_de) {
> if (old_dir != new_dir)
> - ufs_set_link(old_inode, dir_de, dir_page, new_dir, 0);
> - else {
> - kunmap(dir_page);
> - put_page(dir_page);
> - }
> + ufs_set_link(old_inode, dir_de, dir_page,
> + dir_page_addr, new_dir, 0);
> + else
> + ufs_put_page(dir_page, dir_page_addr);
> inode_dec_link_count(old_dir);
> }
> return 0;
>
>
> out_dir:
> - if (dir_de) {
> - kunmap(dir_page);
> - put_page(dir_page);
> - }
> + if (dir_de)
> + ufs_put_page(dir_page, dir_page_addr);
> out_old:
> - kunmap(old_page);
> - put_page(old_page);
> + ufs_put_page(old_page, old_page_addr);
Just pass dir_de and old_de resp. in these two calls of ufs_put_page() - nothing
else is needed...
The bottom line:
* teach your ufs_put_page() to accept any address within the page
* flip the ways you return page and address in ufs_get_page()
* use offset_in_page(addr) instead of these addr - page_address(page)
and you'll get a much smaller patch, with a lot less noise in it.
What's more, offset_in_page() part can be carved out into a separate
commit - it's valid on its own, and it makes both halves easier to
follow.
AFAICS, similar observations apply in your sysvfs patch; the point about
calling conventions for ufs_get_page() definitely applies there, and
stronger than for ufs - those casts are eye-watering...
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