linux-kernel - Re: [GIT PULL] Ceph fixes for 5.1-rc7

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Date:   Sun, 28 Apr 2019 05:38:12 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] Ceph fixes for 5.1-rc7

On Fri, Apr 26, 2019 at 01:30:53PM -0400, Jeff Layton wrote:

> > I _probably_ would take allocation out of the loop (e.g. make it
> > __getname(), called unconditionally) and turned it into the
> > d_path.c-style read_seqbegin_or_lock()/need_seqretry()/done_seqretry()
> > loop, so that the first pass would go under rcu_read_lock(), while
> > the second (if needed) would just hold rename_lock exclusive (without
> > bumping the refcount).  But that's a matter of (theoretical) livelock
> > avoidance, not the locking correctness for ->d_name accesses.
> > 
> 
> Yeah, that does sound better. I want to think about this code a bit

FWIW, is there any reason to insist that the pathname is put into the
beginning of the buffer?  I mean, instead of path + pathlen we might
return path + offset, with the pathname going from path + offset to
path + PATH_MAX - 1 inclusive, with path being the thing eventually
freed.

It's easier to build the string backwards, seeing that we are walking
from leaf to root...