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Subject: Re: linux-5.4.80: "refcount_t: underflow; use-after-free" in
 rpc_async_schedule->rpc_free_task->nfs4_put_copy
From:   Timo Rothenpieler <timo@rothenpieler.org>
To:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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Date:   Mon, 30 Nov 2020 14:12:04 +0100
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On 30.11.2020 13:53, Timo Rothenpieler wrote:
> I don't know for sure if changes to the 5.4 kernel have triggered this, 
> or changes in singularity which now make use of copy_file_range.
> But restarting the nfs server, and then doing a "singularity pull" 
> reliably triggers that dmesg message.
> 
> I found commit 49a361327332c9221438397059067f9b205f690d, but it seems 
> related to the inter ssc stuff, which isn't even present in 5.4.

Quick update: I applied that commit on top of the 5.4.80 Kernel, and 
have not been able to reproduce the issue anymore in a quick test.
Will leave it running like this for a bit and see if it's fixed.

I don't know if this is in any way correct though.