Type mismatch causing stale client loop

Hello,

I didn't see this issue reported already, but then, I didn't do a terribly exhaustive search, so my apologies if this is already known.

I noticed that I was getting looping stale client errors while trying to mount an NFS share (example below):

[  965.926293] nfsd_dispatch: vers 4 proc 1
[  965.973373] nfsv4 compound op #1/1: 35 (OP_SETCLIENTID)
[  966.036158] renewing client (clientid 6f1df70d/00002580)
[  966.099880] nfsv4 compound op ffff880450d51080 opcnt 1 #1: 35: status 0
[  966.179190] nfsv4 compound returned 0
[  966.223447] nfsd_dispatch: vers 4 proc 1
[  966.270475] nfsv4 compound op #1/1: 36 (OP_SETCLIENTID_CONFIRM)
[  966.341487] NFSD stale clientid (6f1df70d/00002580) boot_time 16f1df70d
[  966.420791] nfsv4 compound op ffff880450d51080 opcnt 1 #1: 36: status 10022
[  966.504419] nfsv4 compound returned 10022
[  966.552738] nfsd_dispatch: vers 4 proc 1

The 'stale' error comes from nfs4state.c:

static int
STALE_CLIENTID(clientid_t *clid, struct nfsd_net *nn)

{
    if (clid->cl_boot == nn->boot_time)
        return 0;
    dprintk("NFSD stale clientid (%08x/%08x) boot_time %08lx\n",
        clid->cl_boot, clid->cl_id, nn->boot_time);
    return 1;
}

I thought to myself -- 'Self, it seems statistically unlikely that a legitimately mismatching cl_boot and nn->boot_time would have identical lower 32-bits'.
As it turns out, nn->boot time is defined as time_t (unsigned long / 64 bits on a 64 bit platform), and cl_boot is defined as a u32.
My system time, as you may have guessed, was wildly invalid (2025-ish). However, this does appear to be a legitimate issue in a 64-bit kernel that will crop up in a few years. I was working in 3.10, but I verified that the definitions are identical in the current 3.19 release candidate. Sadly, I don't have the bandwidth (or the expertise) to really understand the ramifications of what seems to be the logical next step, changing cl_boot to be time_t instead of u32. I am hoping that this will be trivial to look at for someone on this list.

Thanks,
-Aaron Pace

I believe it's signed.

cl_boot is an on-the-wire field with space only for 32 bits.

So I think we want to check that clid->cl_boot and nn->boot_time for equality mod 2^32 instead of for strict equality.

That requires assuming that a client will not attempt to reuse stale state given out on a previous server boot that happened some exact multiple of 2^32 seconds (130-some years?) ago. I'm comfortable with that assumption....

--b.