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Date:   Mon, 28 Jun 2021 10:04:08 +0100
From:   Luis Henriques <lhenriques@suse.de>
To:     Jeff Layton <jlayton@kernel.org>
Cc:     Ilya Dryomov <idryomov@gmail.com>, ceph-devel@vger.kernel.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [RFC PATCH] ceph: reduce contention in ceph_check_delayed_caps()
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On Fri, Jun 25, 2021 at 12:54:44PM -0400, Jeff Layton wrote:
<...>
> I'm not sure this approach is viable, unfortunately. Once you've dropped
> the cap_delay_lock, then nothing protects the i_cap_delay_list head
> anymore.
> 
> So you could detach these objects and put them on the private list, and
> then once you drop the spinlock another task could find one of them and
> (e.g.) call __cap_delay_requeue on it, potentially corrupting your list.
> 
> I think we'll need to come up with a different way to do this...

Ugh, yeah I see what you mean.

Another option I can think off is to time-bound this loop, so that it
would stop after finding the first ci->i_hold_caps_max timestamp that was
set *after* the start of the current run.  I'll see if I can come up with
an RFC shortly.

Cheers,
--
Lu?s