don't put symlink bodies in pagecache into highmem

commit 21fc61c7 upstream.

kmap() in page_follow_link_light() needed to go - allowing to hold
an arbitrary number of kmaps for long is a great way to deadlocking
the system.

new helper (inode_nohighmem(inode)) needs to be used for pagecache
symlinks inodes; done for all in-tree cases.  page_follow_link_light()
instrumented to yell about anything missed.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jin Qian <jinqian@google.com>
Signed-off-by: Jin Qian <jinqian@android.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/ext4/inode.c

@@ -4417,6 +4417,7 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 			inode->i_op = &ext4_symlink_inode_operations;
 			ext4_set_aops(inode);
 		}
+		inode_nohighmem(inode);
 	} else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
 	      S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
 		inode->i_op = &ext4_special_inode_operations;

fs/ext4/namei.c

@@ -3151,6 +3151,7 @@ static int ext4_symlink(struct inode *dir,
 	if ((disk_link.len > EXT4_N_BLOCKS * 4)) {
 		if (!encryption_required)
 			inode->i_op = &ext4_symlink_inode_operations;
+		inode_nohighmem(inode);
 		ext4_set_aops(inode);
 		/*
 		 * We cannot call page_symlink() with transaction started

fs/ext4/symlink.c

@@ -45,7 +45,7 @@ static const char *ext4_encrypted_follow_link(struct dentry *dentry, void **cook
 		cpage = read_mapping_page(inode->i_mapping, 0, NULL);
 		if (IS_ERR(cpage))
 			return ERR_CAST(cpage);
-		caddr = kmap(cpage);
+		caddr = page_address(cpage);
 		caddr[size] = 0;
 	}
 
@@ -75,16 +75,12 @@ static const char *ext4_encrypted_follow_link(struct dentry *dentry, void **cook
 	/* Null-terminate the name */
 	if (res <= plen)
 		paddr[res] = '\0';
-	if (cpage) {
-		kunmap(cpage);
+	if (cpage)
 		page_cache_release(cpage);
-	}
 	return *cookie = paddr;
 errout:
-	if (cpage) {
-		kunmap(cpage);
+	if (cpage)
 		page_cache_release(cpage);
-	}
 	kfree(paddr);
 	return ERR_PTR(res);
 }

fs/f2fs/inode.c

@@ -202,6 +202,7 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
 			inode->i_op = &f2fs_encrypted_symlink_inode_operations;
 		else
 			inode->i_op = &f2fs_symlink_inode_operations;
+		inode_nohighmem(inode);
 		inode->i_mapping->a_ops = &f2fs_dblock_aops;
 	} else if (S_ISCHR(inode->i_mode) || S_ISBLK(inode->i_mode) ||
 			S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {

fs/f2fs/namei.c

@@ -351,6 +351,7 @@ static int f2fs_symlink(struct inode *dir, struct dentry *dentry,
 		inode->i_op = &f2fs_encrypted_symlink_inode_operations;
 	else
 		inode->i_op = &f2fs_symlink_inode_operations;
+	inode_nohighmem(inode);
 	inode->i_mapping->a_ops = &f2fs_dblock_aops;
 
 	f2fs_lock_op(sbi);
@@ -942,7 +943,7 @@ static const char *f2fs_encrypted_follow_link(struct dentry *dentry, void **cook
 	cpage = read_mapping_page(inode->i_mapping, 0, NULL);
 	if (IS_ERR(cpage))
 		return ERR_CAST(cpage);
-	caddr = kmap(cpage);
+	caddr = page_address(cpage);
 	caddr[size] = 0;
 
 	/* Symlink is encrypted */
@@ -982,13 +983,11 @@ static const char *f2fs_encrypted_follow_link(struct dentry *dentry, void **cook
 	/* Null-terminate the name */
 	paddr[res] = '\0';
 
-	kunmap(cpage);
 	page_cache_release(cpage);
 	return *cookie = paddr;
 errout:
 	kfree(cstr.name);
 	f2fs_fname_crypto_free_buffer(&pstr);
-	kunmap(cpage);
 	page_cache_release(cpage);
 	return ERR_PTR(res);
 }

fs/inode.c

@@ -2028,3 +2028,9 @@ void inode_set_flags(struct inode *inode, unsigned int flags,
 				  new_flags) != old_flags));
 }
 EXPORT_SYMBOL(inode_set_flags);
+
+void inode_nohighmem(struct inode *inode)
+{
+	mapping_set_gfp_mask(inode->i_mapping, GFP_USER);
+}
+EXPORT_SYMBOL(inode_nohighmem);

include/linux/fs.h

@@ -3066,5 +3066,6 @@ static inline bool dir_relax(struct inode *inode)
 }
 
 extern bool path_noexec(const struct path *path);
+extern void inode_nohighmem(struct inode *inode);
 
 #endif /* _LINUX_FS_H */