linux-kernel - Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem

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Message-ID: <20160114152553.GW17997@ZenIV.linux.org.uk>
Date:	Thu, 14 Jan 2016 15:25:53 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Tomeu Vizoso <tomeu@...euvizoso.net>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Neil Brown <neilb@...e.com>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into
 highmem

On Thu, Jan 14, 2016 at 02:22:51PM +0100, Tomeu Vizoso wrote:
> On 9 December 2015 at 06:34, Al Viro <viro@...iv.linux.org.uk> wrote:
> > From: Al Viro <viro@...iv.linux.org.uk>
> >
> > 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.
> 
> Hi, starting with with this change, I get this oops when installing
> packages into a rootfs in NFS:

Lovely...  So you somehow getting a highmem page out
                page = read_cache_page(&inode->i_data, 0,
                                        (filler_t *)nfs_symlink_filler, inode);
                if (IS_ERR(page))
                        return ERR_CAST(page);
and that - after
                        inode_nohighmem(inode);
(otherwise you wouldn't get nfs_symlink_inode_operations on that inode).

Could you add
	printk(KERN_ERR "i_data = %p, i_mapping = %p, flags: %lx\n",
		&inode->i_data,
		inode->i_mapping,
		(unsigned long)inode->i_data.flags);
right before the return from nfs_get_link() and see what it prints?