Re: [PATCH 3/8] staging: erofs: add error handling for xattr submodule

Dan Carpenter
2018-08-13T11:47:53Z

> -static void xattr_iter_fixup(struct xattr_iter *it)
> +static inline int xattr_iter_fixup(struct xattr_iter *it)
> {
> - if (unlikely(it->ofs >= EROFS_BLKSIZ)) {
> - xattr_iter_end(it, true);
> + if (likely(it->ofs < EROFS_BLKSIZ))
> + return 0;
>
> - it->blkaddr += erofs_blknr(it->ofs);
> - it->page = erofs_get_meta_page_nofail(it->sb,
> - it->blkaddr, false);
> - BUG_ON(IS_ERR(it->page));
> + xattr_iter_end(it, true);
>
> - it->kaddr = kmap_atomic(it->page);
> - it->ofs = erofs_blkoff(it->ofs);
> + it->blkaddr += erofs_blknr(it->ofs);
> +
> + it->page = erofs_get_meta_page(it->sb, it->blkaddr, false);
> + if (IS_ERR(it->page)) {
> + it->page = NULL;
> + return PTR_ERR(it->page);

This is returning PTR_ERR(NULL) which is success. There is a smatch
test for this and maybe other static checkers as well so it would have
been caught very quickly.

> }
> +
> + it->kaddr = kmap_atomic(it->page);
> + it->ofs = erofs_blkoff(it->ofs);
> + return 0;
> }
>
> static int inline_xattr_iter_begin(struct xattr_iter *it,
> @@ -134,22 +154,25 @@ static int inline_xattr_iter_begin(struct xattr_iter *it,
> it->blkaddr = erofs_blknr(iloc(sbi, vi->nid) + inline_xattr_ofs);
> it->ofs = erofs_blkoff(iloc(sbi, vi->nid) + inline_xattr_ofs);
>
> - it->page = erofs_get_inline_page_nofail(inode, it->blkaddr);
> - BUG_ON(IS_ERR(it->page));
> - it->kaddr = kmap_atomic(it->page);
> + it->page = erofs_get_inline_page(inode, it->blkaddr);
> + if (IS_ERR(it->page))
> + return PTR_ERR(it->page);
>
> + it->kaddr = kmap_atomic(it->page);
> return vi->xattr_isize - xattr_header_sz;
> }
>
> static int xattr_foreach(struct xattr_iter *it,
> - struct xattr_iter_handlers *op, unsigned *tlimit)
> + const struct xattr_iter_handlers *op, unsigned *tlimit)
> {
> struct erofs_xattr_entry entry;
> unsigned value_sz, processed, slice;
> int err;
>
> /* 0. fixup blkaddr, ofs, ipage */
> - xattr_iter_fixup(it);
> + err = xattr_iter_fixup(it);
> + if (unlikely(err))
> + return err;
>
> /*
> * 1. read xattr entry to the memory,
> @@ -181,7 +204,9 @@ static int xattr_foreach(struct xattr_iter *it,
> if (it->ofs >= EROFS_BLKSIZ) {
> BUG_ON(it->ofs > EROFS_BLKSIZ);
>
> - xattr_iter_fixup(it);
> + err = xattr_iter_fixup(it);
> + if (unlikely(err))
> + goto out;
> it->ofs = 0;
> }
>
> @@ -213,7 +238,10 @@ static int xattr_foreach(struct xattr_iter *it,
> while (processed < value_sz) {
> if (it->ofs >= EROFS_BLKSIZ) {
> BUG_ON(it->ofs > EROFS_BLKSIZ);
> - xattr_iter_fixup(it);
> +
> + err = xattr_iter_fixup(it);
> + if (unlikely(err))
> + goto out;
> it->ofs = 0;
> }
>
> @@ -273,7 +301,7 @@ static void xattr_copyvalue(struct xattr_iter *_it,
> memcpy(it->buffer + processed, buf, len);
> }
>
> -static struct xattr_iter_handlers find_xattr_handlers = {
> +static const struct xattr_iter_handlers find_xattr_handlers = {
> .entry = xattr_entrymatch,
> .name = xattr_namematch,
> .alloc_buffer = xattr_checkbuffer,
> @@ -294,8 +322,11 @@ static int inline_getxattr(struct inode *inode, struct getxattr_iter *it)
> ret = xattr_foreach(&it->it, &find_xattr_handlers, &remaining);
> if (ret >= 0)
> break;
> +
> + if (unlikely(ret != -ENOATTR)) /* -ENOMEM, -EIO, etc. */

I have held off commenting on all the likely/unlikely annotations we
are adding because I don't know what the fast paths are in this code.
However, this is clearly an error path here, not on a fast path.

Generally the rule on likely/unlikely is that they hurt readability so
we should only add them if it makes a difference in benchmarking.

> + break;
> }
> - xattr_iter_end(&it->it, true);
> + xattr_iter_end_final(&it->it);
>
> return ret < 0 ? ret : it->buffer_size;
> }
> @@ -318,9 +349,10 @@ static int shared_getxattr(struct inode *inode, struct getxattr_iter *it)
> if (i)
> xattr_iter_end(&it->it, true);
>
> - it->it.page = erofs_get_meta_page_nofail(sb,
> - blkaddr, false);
> - BUG_ON(IS_ERR(it->it.page));
> + it->it.page = erofs_get_meta_page(sb, blkaddr, false);
> + if (IS_ERR(it->it.page))
> + return PTR_ERR(it->it.page);
> +
> it->it.kaddr = kmap_atomic(it->it.page);
> it->it.blkaddr = blkaddr;
> }
> @@ -328,9 +360,12 @@ static int shared_getxattr(struct inode *inode, struct getxattr_iter *it)
> ret = xattr_foreach(&it->it, &find_xattr_handlers, NULL);
> if (ret >= 0)
> break;
> +
> + if (unlikely(ret != -ENOATTR)) /* -ENOMEM, -EIO, etc. */
> + break;
> }
> if (vi->xattr_shared_count)
> - xattr_iter_end(&it->it, true);
> + xattr_iter_end_final(&it->it);
>
> return ret < 0 ? ret : it->buffer_size;
> }
> @@ -355,7 +390,9 @@ int erofs_getxattr(struct inode *inode, int index,
> if (unlikely(name == NULL))
> return -EINVAL;
>
> - init_inode_xattrs(inode);
> + ret = init_inode_xattrs(inode);
> + if (unlikely(ret < 0))
> + return ret;
>
> it.index = index;
>
> @@ -498,7 +535,7 @@ static int xattr_skipvalue(struct xattr_iter *_it,
> return 1;

Not related to your patch but what does "return 1;" mean here? It's
weird to me that xattr_skipvalue() doesn't use value_sz at all. I can't
decide if the function always succeeds or always fails.

The xattr_skipvalue/alloc_buffer function is called like this:

err = op->alloc_buffer(it, value_sz);
if (err) {
it->ofs += value_sz;
goto out;
}

It looks like if we hit an error, we increase it->ofs. All the other
error paths in this function take a negative error and increase it->ofs
so this looks like an error path. The goto out look like this:

/* we assume that ofs is aligned with 4 bytes */
it->ofs = EROFS_XATTR_ALIGN(it->ofs);
return err;

So we return 1 here and the callers all treat it at success... There
needs to be some documentation for what positive returns mean.

regards,
dan carpenter