linux-kernel - Re: [RFC PATCH] mm: truncate: flush lru cache for evicted inode

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Date: Mon, 17 Jun 2024 09:57:58 +0200
From: Jan Kara <jack@...e.cz>
To: Hillf Danton <hdanton@...a.com>
Cc: Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
	syzbot+d79afb004be235636ee8@...kaller.appspotmail.com,
	linux-fsdevel@...r.kernel.org, linux-nilfs@...r.kernel.org,
	Ryusuke Konishi <konishi.ryusuke@...il.com>
Subject: Re: [RFC PATCH] mm: truncate: flush lru cache for evicted inode

On Sun 16-06-24 10:39:51, Hillf Danton wrote:
> 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

OK, so based on syzbot results this seems to be a bug in
nilfs_evict_inode() (likely caused by corrupted filesystem so that root
inode's link count was 0 and hence was getting deleted on iput()). I guess
nilfs maintainers need to address these with more consistency checks of
metadata when loading them...

									Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR