On Thu, 19 Jun 2008 10:11:09 +1000
NeilBrown <neilb@xxxxxxx> 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 "try again later" by returning
> nfserr_jukebox. The client will resend and - if the server is
> restarted - the write will (hopefully) be successful and everyone will
> be happy.
>
> 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 where writes appeared to fail.
>
>
> Signed-off-by: Neil Brown <neilb@xxxxxxx>
>
> ### 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 2008-06-19 10:06:36.000000000 +1000
> +++ ./fs/nfsd/nfsproc.c 2008-06-19 10:07:58.000000000 +1000
> @@ -614,6 +614,7 @@ nfserrno (int errno)
> #endif
> { nfserr_stale, -ESTALE },
> { nfserr_jukebox, -ETIMEDOUT },
> + { nfserr_jukebox, -ERESTARTSYS },
> { nfserr_dropit, -EAGAIN },
> { nfserr_dropit, -ENOMEM },
> { nfserr_badname, -ESRCH },
> --
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>
No objection to the patch, but what signal was being sent to nfsd when
you saw this? If it's anything but a SIGKILL, then I wonder if we have
a race that we need to deal with. My understanding is that we have nfsd
flip between 2 sigmasks to prevent anything but a SIGKILL from being
delivered while we're handling the local filesystem operation.
>From nfsd():
----------[snip]-----------
sigprocmask(SIG_SETMASK, &shutdown_mask, NULL);
/*
* Find a socket with data available and call its
* recvfrom routine.
*/
while ((err = svc_recv(rqstp, 60*60*HZ)) == -EAGAIN)
;
if (err < 0)
break;
update_thread_usage(atomic_read(&nfsd_busy));
atomic_inc(&nfsd_busy);
/* Lock the export hash tables for reading. */
exp_readlock();
/* Process request with signals blocked. */
sigprocmask(SIG_SETMASK, &allowed_mask, NULL);
svc_process(rqstp);
----------[snip]-----------
What happens if this catches a SIGINT after the err<0 check, but before
the mask is set to allowed_mask? Does svc_process() then get called with
a signal pending?
--
Jeff Layton <jlayton@xxxxxxxxxx>
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