linux-kernel - Re: [RFC][PATCH 07/10] orangefs: Use RCU for destroy

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Date:   Sun, 26 Feb 2017 17:20:42 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Mike Marshall <hubcap@...ibond.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Chris Mason <clm@...com>, LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC][PATCH 07/10] orangefs: Use RCU for destroy_inode

On Sun, Feb 26, 2017 at 4:34 PM, Mike Marshall <hubcap@...ibond.com> wrote:
> Since Orangefs uses ref-walk, not rcu-walk, this patch with call_rcu
> has seemed weird to me.

Even if orangefs never really allows RCU walking, the VFS layer will
look up dentries - and look at their inodes - from RCU. It will then
call into the filesystem

So even if orangefs always returned ECHILD (it doesn't - it has a
timeout) - we'd be following the dentry inode pointer in jus a RCU
read region.

           Linus