linux-kernel - Re: [Patch 0/2] NFSD: Fix server hang when there are multiple layout conflicts

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Message-ID: <20251107133045.GA5158@lst.de>
Date: Fri, 7 Nov 2025 14:30:45 +0100
From: Christoph Hellwig <hch@....de>
To: Dai Ngo <dai.ngo@...cle.com>
Cc: chuck.lever@...cle.com, jlayton@...nel.org, neilb@...mail.net,
	okorniev@...hat.com, tom@...pey.com, hch@....de,
	alex.aring@...il.com, viro@...iv.linux.org.uk, brauner@...nel.org,
	jack@...e.cz, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: [Patch 0/2] NFSD: Fix server hang when there are multiple
 layout conflicts

On Thu, Nov 06, 2025 at 09:05:24AM -0800, Dai Ngo wrote:
> When a layout conflict triggers a call to __break_lease, the function
> nfsd4_layout_lm_break clears the fl_break_time timeout before sending
> the CB_LAYOUTRECALL. As a result, __break_lease repeatedly restarts
> its loop, waiting indefinitely for the conflicting file lease to be
> released.
> 
> If the number of lease conflicts matches the number of NFSD threads (which
> defaults to 8), all available NFSD threads become occupied. Consequently,
> there are no threads left to handle incoming requests or callback replies,
> leading to a total hang of the NFS server.
> 
> This issue is reliably reproducible by running the Git test suite on a
> configuration using SCSI layout.

I guess we need to implement asynchronous breaking of leases.  Which
conceptually shouldn't be too hard.