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Message-ID: <055f76be-226f-4b15-8e7b-13f78dba10c5@redhat.com>
Date:   Wed, 25 Oct 2023 13:37:30 -0400
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Subject: Re: [PATCH 0/6 nfs-utils v2] fixes for error handling in nfsd_fh
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To:     NeilBrown <neilb@suse.de>
Cc:     linux-nfs@vger.kernel.org,
        Trond Myklebust <trond.myklebust@hammerspace.com>
References: <20231023021052.5258-1-neilb@suse.de>
From:   Steve Dickson <steved@redhat.com>
In-Reply-To: <20231023021052.5258-1-neilb@suse.de>
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On 10/22/23 9:58 PM, NeilBrown wrote:
> Hi,
>   this is a revised version of my previous series with the same name.
>   This first two patches are unchanged.
>   The third patch, which was an RFC, has been replaced with the last
>   patch which actually addresses the issue rather than skirting
>   around it.
> 
>   Patch 3 here is a revert of a change I noticed while exploring the
>   code.  cache_open() must be called BEFORE forking workers, as explained
>   in that patch.
>   Patches 4 and 5 factor our common code which makes the final patch
>   simpler.
> 
>   The core issue is that sometimes mountd (or exportd) cannot give a
>   definitey "yes" or "no" to a request to map an fsid to a path name.
>   In these cases the only safe option is to delay and try again.
> 
>   This only becomes relevant if a filesystem is mounted by a client, then
>   the server restarts (or the export cache is flushed) and the client
>   tries to use a filehandle that it already has, but that server cannot
>   find it and cannot be sure it doesn't exist.  This can happen when an
>   export is marked "mountpoint" or when a re-exported NFS filesystem
>   cannot contact the server and reports an ETIMEDOUT error.  In these
>   cases we want the client to continue waiting (which it does) and also
>   want mountd/exportd to periodically check if the target filesystem has
>   come back (which it currently does not).
>   With the current code, once this situation happens and the client is
>   waiting, the client will continue to wait indefintely even if the
>   target filesytem becomes available.  The client can only continue if
>   the NFS server is restarted or the export cache is flushed.  After the
>   ptsch, then within 2 minutes of the target filesystem becoming
>   available again, mountd will tell the kernel and when the client asks
>   again it will get be allowed to proceed.
> 
> NeilBrown
> 
> 
>   [PATCH 1/6] export: fix handling of error from match_fsid()
>   [PATCH 2/6] export: add EACCES to the list of known
>   [PATCH 3/6] export: move cache_open() before workers are forked.
>   [PATCH 4/6] Move fork_workers() and wait_for_workers() in cache.c
>   [PATCH 5/6] Share process_loop code between mountd and exportd.
>   [PATCH 6/6] cache: periodically retry requests that couldn't be
> 
Committed... (tag: nfs-utils-2-6-4-rc5)

steved.