linux-kernel - Re: [PATCH RFC] nfsd: avoid recursive locking through fsnotify

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Date:   Fri, 18 Mar 2022 18:45:04 -0700
From:   Khazhy Kumykov <khazhy@...gle.com>
To:     Trond Myklebust <trondmy@...merspace.com>
Cc:     "bfields@...ldses.org" <bfields@...ldses.org>,
        "chuck.lever@...cle.com" <chuck.lever@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] nfsd: avoid recursive locking through fsnotify

On Fri, Mar 18, 2022 at 5:36 PM Trond Myklebust <trondmy@...merspace.com> wrote:
>
> Isn't that stack trace showing a slab direct reclaim, and not a
> filesystem writeback situation?
>
> Does memalloc_nofs_save()/restore() really fix this problem? It seems
> to me that it cannot, particularly since knfsd is not a filesystem, and
> so does not ever handle writeback of dirty pages.

Ah you're right. An alternative would be delaying the destroy_mark,
which I am noticing now that, on mainline, the shrinker calls
nfsd_file_dispose_list_delayed, something missing from the version of
5.4 I was looking at.

To my reading 9542e6a643fc6 ("nfsd: Containerise filecache
laundrette") should have the effect of fixing this deadlock (and the
message does explicitly call out notifier deadlocks) - maybe something
to send towards stable?
>
>
> Cc: the linux-mm mailing list in search of answers to the above 2
> questions.
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@...merspace.com
>
>

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