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

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Date:	Mon, 16 Jun 2008 08:39:53 -0400
From:	Peter Staubach <staubach@...hat.com>
To:	NeilBrown <neilb@...e.de>
CC:	"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.

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.

       ps

> 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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