linux-kernel - Re: Does ceph_fill_inode() mishandle I

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Message-ID: <1675858.1741909671@warthog.procyon.org.uk>
Date: Thu, 13 Mar 2025 23:47:51 +0000
From: David Howells <dhowells@...hat.com>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>
Cc: dhowells@...hat.com, "slava@...eyko.com" <slava@...eyko.com>,
    Xiubo Li <xiubli@...hat.com>,
    "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
    "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
    "brauner@...nel.org" <brauner@...nel.org>,
    "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
    Alex Markuze <amarkuze@...hat.com>,
    "jlayton@...nel.org" <jlayton@...nel.org>,
    "idryomov@...il.com" <idryomov@...il.com>,
    "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
Subject: Re: Does ceph_fill_inode() mishandle I_NEW?

Viacheslav Dubeyko <Slava.Dubeyko@....com> wrote:

> As far as I can see, ceph_fill_inode() has comment: "Populate an inode based
> on info from mds. May be called on new or existing inodes". It sounds to me
> that particular CephFS kernel client could have obsolete state of inode
> compared with MDS's state. And we need to "re-new" the existing inode with
> the actual state that we received from MDS side. My vision is that we need
> to take into account the distributed nature of Ceph and inode metadata can
> be updated from multiple CephFS kernel client instances. Am I right here?

As I mentioned in my reply to Jeff, I'm thinking of what happens in the event
that we have a file that has hard links in several directories in a situation
where several of those links are looked up simultaneously.  Can we end up with
ceph_fill_inode() being run in parallel on several threads on the same inode?

Actually, the use of ci->i_ceph_lock looks like it should make it safe, now
that I look at it again.

David