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From: Hillf Danton <hdanton@sina.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm@kvack.org,
	Jan Kara <jack@suse.cz>,
	linux-kernel@vger.kernel.org,
	syzbot+d79afb004be235636ee8@syzkaller.appspotmail.com,
	linux-fsdevel@vger.kernel.org,
	linux-nilfs@vger.kernel.org,
	Ryusuke Konishi <konishi.ryusuke@gmail.com>
Subject: Re: [RFC PATCH] mm: truncate: flush lru cache for evicted inode
Date: Sun, 16 Jun 2024 10:39:51 +0800
Message-Id: <20240616023951.1250-1-hdanton@sina.com>
In-Reply-To: <Zm39RkZMjHdui8nh@casper.infradead.org>
References: 
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On Sat, 15 Jun 2024 21:44:54 +0100 Matthew Wilcox wrote:
> 
> I suspect this would trigger:
> 
> +++ b/fs/inode.c
> @@ -282,6 +282,7 @@ static struct inode *alloc_inode(struct super_block *sb)
>  void __destroy_inode(struct inode *inode)
>  {
>         BUG_ON(inode_has_buffers(inode));
> +       BUG_ON(inode->i_data.nrpages);
>         inode_detach_wb(inode);
>         security_inode_free(inode);
>         fsnotify_inode_delete(inode);
> 
Yes, it was triggered [1]

[1] https://lore.kernel.org/lkml/00000000000084b401061af6ab80@google.com/

and given trigger after nrpages is checked in clear_inode(),

	iput(inode)
	evict(inode)
	truncate_inode_pages_final(&inode->i_data);
	clear_inode(inode);
	destroy_inode(inode);

why is folio added to exiting mapping?

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  83a7eefedc9b

--- x/mm/filemap.c
+++ y/mm/filemap.c
@@ -870,6 +870,7 @@ noinline int __filemap_add_folio(struct
 	folio_ref_add(folio, nr);
 	folio->mapping = mapping;
 	folio->index = xas.xa_index;
+	BUG_ON(mapping_exiting(mapping));
 
 	for (;;) {
 		int order = -1, split_order = 0;
--