Re: [PATCH v2] pNFS: avoid repeatedly cancelling I/O for the same lseg

[Trond Myklebust]

On Thu, 2026-11-05 at 00:01 +0000, Tim Menninger wrote:
> Commit b739a5bd9d9f ("NFSv4/flexfiles: Cancel I/O if the layout is
> recalled or revoked") added I/O cancellation when a layout segment is
> invalidated while outstanding references remain.
> 
> The invalid segment stays on the layout's segment list until those
> references drain. Subsequent scans can find it again and repeatedly
> invoke the layout driver's cancel_io() callback. For flexfiles, this
> cancels matching RPC tasks and disconnects data server RPC clients.
> During RPC/RDMA data server recovery, repeated cancellation can cause
> a
> reconnect loop that consumes essentially all client CPU and prevents
> forward progress.

This claim isn't making sense to me.

If a layout segment is recalled or revoked, we should always be
clearing the NFS_LSEG_VALID flag bit in order to prevent it being
looked up again. New RPC calls should not be able to add that layout
segment.

So the only thing that can be found on a second run of
rpc_cancel_tasks() is a task that has been attempted cancelled
previously, but for which that cancel failed.
If you're seeing actual spinning, where the RPC call is just being
requeued by the rpc_call_done() callback, then we need to look at why
the latter is failing to handle the situation correctly.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trondmy@xxxxxxxxxx, trond.myklebust@xxxxxxxxxxxxxxx