linux-kernel - Re: [PATCH] knfsd: nfsd: Handle ERESTARTSYS from syscalls.

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Date:	Mon, 16 Jun 2008 11:09:52 -0400
From:	"Chuck Lever" <chucklever@...il.com>
To:	"Peter Staubach" <staubach@...hat.com>
Cc:	NeilBrown <neilb@...e.de>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] knfsd: nfsd: Handle ERESTARTSYS from syscalls.

On Mon, Jun 16, 2008 at 8:39 AM, Peter Staubach <staubach@...hat.com> wrote:
> NeilBrown wrote:
>>
>> OCFS2 can return -ERESTARTSYS from write requests (and possibly
>> elsewhere) if there is a signal pending.
>>
>> If nfsd is shutdown (by sending a signal to each thread) while there
>> is still an IO load from the client, each thread could handle one last
>> request with a signal pending.  This can result in -ERESTARTSYS
>> which is not understood by nfserrno() and so is reflected back to
>> the client as nfserr_io aka -EIO.  This is wrong.
>>
>> Instead, interpret ERESTARTSYS to mean "don't send a reply".
>> The client will resend and - if the server is restarted - the write will
>> (hopefully) be successful and everyone will be happy.
>>
>>
>
> Why not handle -ERESTARTSYS in the same fashion as -ETIMEDOUT, ie.
> leading to a EJUKEBOX sort of error being returned if possible?
>
> Simply not returning is a bad thing to do for anything other than
> NFSv2.  It is especially bad for NFSv4.

Actually, the NFSv4 spec *requires* the server to reply to every request.

Not replying means an NFSv4 client connected via NFSv4 will have to
disconnect and retransmit.  That should be avoided if at all possible.

I think an error reply is much better than no reply in nearly every
case.  NFS3ERR_JUKEBOX/NFS4ERR_DELAY is an interesting idea, but
something else again will probably be required for v4.1 with sessions.

>> Signed-off-by: Neil Brown <neilb@...e.de>
>>
>> ### Diffstat output
>>  ./fs/nfsd/nfsproc.c |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> ----
>> Funny how the shortest patches sometimes have the longest
>> descriptions.
>>
>> The symptom that I narrowed down to this was:
>>   copy a large file via NFS to an OCFS2 filesystem, and restart
>>   the nfs server during the copy.
>>   The 'cp' might get an -EIO, and the file will be corrupted -
>>   presumably holes in the middle were writes appeared to fail.
>>
>> diff .prev/fs/nfsd/nfsproc.c ./fs/nfsd/nfsproc.c
>> --- .prev/fs/nfsd/nfsproc.c     2008-06-13 21:31:53.000000000 +1000
>> +++ ./fs/nfsd/nfsproc.c 2008-06-13 21:31:57.000000000 +1000
>> @@ -614,6 +614,7 @@ nfserrno (int errno)
>>  #endif
>>                { nfserr_stale, -ESTALE },
>>                { nfserr_jukebox, -ETIMEDOUT },
>> +               { nfserr_dropit, -ERESTARTSYS },
>>                { nfserr_dropit, -EAGAIN },
>>                { nfserr_dropit, -ENOMEM },
>>                { nfserr_badname, -ESRCH },
>>
>> ### Diffstat output
>>  ./fs/nfsd/nfsproc.c |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff .prev/fs/nfsd/nfsproc.c ./fs/nfsd/nfsproc.c
>> --- .prev/fs/nfsd/nfsproc.c     2008-06-13 21:31:53.000000000 +1000
>> +++ ./fs/nfsd/nfsproc.c 2008-06-13 21:31:57.000000000 +1000
>> @@ -614,6 +614,7 @@ nfserrno (int errno)
>>  #endif
>>                { nfserr_stale, -ESTALE },
>>                { nfserr_jukebox, -ETIMEDOUT },
>> +               { nfserr_dropit, -ERESTARTSYS },
>>                { nfserr_dropit, -EAGAIN },
>>                { nfserr_dropit, -ENOMEM },
>>                { nfserr_badname, -ESRCH },
>> --
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>>
>
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