erofs: better erofs symlink stuffs

Fix as Christoph suggested [1] [2], "remove is_inode_fast_symlink
and just opencode it in the few places using it"

and
"Please just set the ops directly instead of obsfucating that in
a single caller, single line inline function.  And please set it
instead of the normal symlink iops in the same place where you
also set those."

[1] https://lore.kernel.org/r/20190830163910.GB29603@infradead.org/
[2] https://lore.kernel.org/r/20190829102426.GE20598@infradead.org/Reported-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190904020912.63925-13-gaoxiang25@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/erofs/inode.c

@@ -127,35 +127,25 @@ static int read_inode(struct inode *inode, void *data)
 	return -EFSCORRUPTED;
 }
 
-/*
- * try_lock can be required since locking order is:
- *   file data(fs_inode)
- *        meta(bd_inode)
- * but the majority of the callers is "iget",
- * in that case we are pretty sure no deadlock since
- * no data operations exist. However I tend to
- * try_lock since it takes no much overhead and
- * will success immediately.
- */
-static int fill_inline_data(struct inode *inode, void *data,
+static int erofs_fill_symlink(struct inode *inode, void *data,
 			      unsigned int m_pofs)
 {
 	struct erofs_inode *vi = EROFS_I(inode);
 	struct erofs_sb_info *sbi = EROFS_I_SB(inode);
+	char *lnk;
 
-	/* should be tail-packing data inline */
-	if (vi->datalayout != EROFS_INODE_FLAT_INLINE)
+	/* if it cannot be handled with fast symlink scheme */
+	if (vi->datalayout != EROFS_INODE_FLAT_INLINE ||
+	    inode->i_size >= PAGE_SIZE) {
+		inode->i_op = &erofs_symlink_iops;
 		return 0;
+	}
 
-	/* fast symlink */
-	if (S_ISLNK(inode->i_mode) && inode->i_size < PAGE_SIZE) {
-		char *lnk = erofs_kmalloc(sbi, inode->i_size + 1, GFP_KERNEL);
-
+	lnk = erofs_kmalloc(sbi, inode->i_size + 1, GFP_KERNEL);
 	if (!lnk)
 		return -ENOMEM;
 
 	m_pofs += vi->inode_isize + vi->xattr_isize;
-
 	/* inline symlink data shouldn't cross page boundary as well */
 	if (m_pofs + inode->i_size > PAGE_SIZE) {
 		kfree(lnk);
@@ -169,8 +159,7 @@ static int fill_inline_data(struct inode *inode, void *data,
 	lnk[inode->i_size] = '\0';
 
 	inode->i_link = lnk;
-		set_inode_fast_symlink(inode);
-	}
+	inode->i_op = &erofs_fast_symlink_iops;
 	return 0;
 }
 
@@ -217,8 +206,9 @@ static int fill_inode(struct inode *inode, int isdir)
 			inode->i_fop = &erofs_dir_fops;
 			break;
 		case S_IFLNK:
-			/* by default, page_get_link is used for symlink */
-			inode->i_op = &erofs_symlink_iops;
+			err = erofs_fill_symlink(inode, data, ofs);
+			if (err)
+				goto out_unlock;
 			inode_nohighmem(inode);
 			break;
 		case S_IFCHR:
@@ -237,11 +227,7 @@ static int fill_inode(struct inode *inode, int isdir)
 			err = z_erofs_fill_inode(inode);
 			goto out_unlock;
 		}
-
 		inode->i_mapping->a_ops = &erofs_raw_access_aops;
-
-		/* fill last page if inline data is available */
-		err = fill_inline_data(inode, data, ofs);
 	}
 
 out_unlock:

fs/erofs/internal.h

@@ -479,16 +479,6 @@ extern const struct inode_operations erofs_generic_iops;
 extern const struct inode_operations erofs_symlink_iops;
 extern const struct inode_operations erofs_fast_symlink_iops;
 
-static inline void set_inode_fast_symlink(struct inode *inode)
-{
-	inode->i_op = &erofs_fast_symlink_iops;
-}
-
-static inline bool is_inode_fast_symlink(struct inode *inode)
-{
-	return inode->i_op == &erofs_fast_symlink_iops;
-}
-
 struct inode *erofs_iget(struct super_block *sb, erofs_nid_t nid, bool dir);
 int erofs_getattr(const struct path *path, struct kstat *stat,
 		  u32 request_mask, unsigned int query_flags);

fs/erofs/super.c

@@ -40,10 +40,9 @@ static void free_inode(struct inode *inode)
 {
 	struct erofs_inode *vi = EROFS_I(inode);
 
-	/* be careful RCU symlink path (see ext4_inode_info->i_data)! */
-	if (is_inode_fast_symlink(inode))
+	/* be careful of RCU symlink path */
+	if (inode->i_op == &erofs_fast_symlink_iops)
 		kfree(inode->i_link);
-
 	kfree(vi->xattr_shared_xattrs);
 
 	kmem_cache_free(erofs_inode_cachep, vi);