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From:   "NeilBrown" <neilb@suse.de>
To:     "Olga Kornievskaia" <olga.kornievskaia@gmail.com>
Cc:     trond.myklebust@hammerspace.com, anna.schumaker@netapp.com,
        linux-nfs@vger.kernel.org
Subject: Re: [PATCH v1 0/3] modify xprt state using sysfs
In-reply-to: <20210603225907.19981-1-olga.kornievskaia@gmail.com>
References: <20210603225907.19981-1-olga.kornievskaia@gmail.com>
Date:   Fri, 04 Jun 2021 09:56:59 +1000
Message-id: <162276461931.16225.7591153378472996760@noble.neil.brown.name>
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On Fri, 04 Jun 2021, Olga Kornievskaia wrote:
> From: Olga Kornievskaia <kolga@netapp.com>
> 
> When a transport gets stuck, it is desired to be able to move the tasks
> that have been stuck/queued on that transport to another. 

This is interesting.....
A long-standing problem with NFS is that it is tricky to reliably
unmount a filesystem if the network is not responding.  It is possible,
but you need to identify all the processes blocked on the filesystem and
SIGKILL them.
My most recent exposure to this was when shutdown hung for someone
because NetworkManager shutdown the wifi before NFS filesystems were
unmounted.   This is arguably a config error, but the same problem could
happen with a power-outage instead of networkmanage breaking the wifi.

It would be nice to be able to forcibly unmount filesystems.  e.g.  mark
the transport as dead in such a way that all requests report EIO (or
similar).
This is obviously a big hammer, probably bigger than justified for use
with "umount -f", but sometimes it is a necessary hammer.

Could your work lead to being able to do this?  Could I write a shutdown
script that runs when there is no more network and no expectation of any
network ever again, and which marks all transports as dead - and then
wakes up all pending rpc tasks?

Thanks,
NeilBrown