linux-kernel - Re: PROBLEM: NFS client IO fails with ERESTARTSYS when another mount point with the same export is unmounted with force [NFS] [SUNRPC]

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Date: Fri, 23 Feb 2024 11:44:07 +0800
From: Zhitao Li <zhitao.li@...rtx.com>
To: Trond Myklebust <trondmy@...merspace.com>
Cc: "chuck.lever@...cle.com" <chuck.lever@...cle.com>, "kolga@...app.com" <kolga@...app.com>, 
	"anna@...nel.org" <anna@...nel.org>, "tom@...pey.com" <tom@...pey.com>, 
	"jlayton@...nel.org" <jlayton@...nel.org>, "neilb@...e.de" <neilb@...e.de>, 
	"Dai.Ngo@...cle.com" <Dai.Ngo@...cle.com>, "huangping@...rtx.com" <huangping@...rtx.com>, 
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: PROBLEM: NFS client IO fails with ERESTARTSYS when another mount
 point with the same export is unmounted with force [NFS] [SUNRPC]

Thanks for Trond's reply.

ERESTARTSYS is an unknown error in application level.  Maybe EIO or
EINTR can be more suitable.

Best regards,
Zhitao Li, at SmartX

On Thu, Feb 22, 2024 at 11:20 PM Trond Myklebust
<trondmy@...merspace.com> wrote:
>
> On Thu, 2024-02-22 at 06:05 -0500, Jeff Layton wrote:
> > On Wed, 2024-02-21 at 13:48 +0000, Trond Myklebust wrote:
> > > On Wed, 2024-02-21 at 16:20 +0800, Zhitao Li wrote:
> > > > [You don't often get email from zhitao.li@...rtx.com. Learn why
> > > > this
> > > > is important at https://aka.ms/LearnAboutSenderIdentification ]
> > > >
> > > > Hi, everyone,
> > > >
> > > > - Facts:
> > > > I have a remote NFS export and I mount the same export on two
> > > > different directories in my OS with the same options. There is an
> > > > inflight IO under one mounted directory. And then I unmount
> > > > another
> > > > mounted directory with force. The inflight IO ends up with
> > > > "Unknown
> > > > error 512", which is ERESTARTSYS.
> > > >
> > >
> > > All of the above is well known. That's because forced umount
> > > affects
> > > the entire filesystem. Why are you using it here in the first
> > > place? It
> > > is not intended for casual use.
> > >
> >
> > While I agree Trond's above statement, the kernel is not supposed to
> > leak error codes that high into userland. Are you seeing ERESTARTSYS
> > being returned to system calls? If so, which ones?
>
> The point of forced umount is to kill all RPC calls associated with the
> filesystem in order to unblock the umount. Basically, it triggers this
> code before the unmount starts:
>
> void nfs_umount_begin(struct super_block *sb)
> {
>         struct nfs_server *server;
>         struct rpc_clnt *rpc;
>
>         server = NFS_SB(sb);
>         /* -EIO all pending I/O */
>         rpc = server->client_acl;
>         if (!IS_ERR(rpc))
>                 rpc_killall_tasks(rpc);
>         rpc = server->client;
>         if (!IS_ERR(rpc))
>                 rpc_killall_tasks(rpc);
> }
>
> So yes, that does signal all the way up to the application level, and
> it is very much intended to do so.
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@...merspace.com
>
>