Re: [PATCH 2/4] pnfs_submit: Only update stateid if it is more recent than current

[Benny Halevy <bhalevy@panasas.com>]

On 2010-10-08 10:13, P.B.Shelley wrote:
> On Thu, Oct 7, 2010 at 10:06 PM, Benny Halevy <bhalevy@panasas.com> wrote:
>> On 2010-10-07 10:01, Fred Isaman wrote:
>>> On Thu, Oct 7, 2010 at 9:34 AM, Benny Halevy <bhalevy@panasas.com> wrote:
>>>> On 2010-10-06 16:35, Fred Isaman wrote:
>>>>> Right now, when we set the stateid, we blindly overwrite the current
>>>>> one, allowing the seqid to incorrectly roll backward.
>>>>>
>>>>> Signed-off-by: Fred Isaman <iisaman@netapp.com>
>>>>> ---
>>>>>  fs/nfs/pnfs.c |   38 ++++++++++++++++++++++++++++++++------
>>>>>  1 files changed, 32 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
>>>>> index 39bce9b..555955b 100644
>>>>> --- a/fs/nfs/pnfs.c
>>>>> +++ b/fs/nfs/pnfs.c
>>>>> @@ -459,16 +459,42 @@ pnfs_destroy_all_layouts(struct nfs_client *clp)
>>>>>       }
>>>>>  }
>>>>>
>>>>> +/* update lo->stateid with new if is more recent
>>>>> + *
>>>>> + * lo->stateid could be the open stateid, in which case we just use what given.
>>>>> + */
>>>>>  static void
>>>>>  pnfs_set_layout_stateid(struct pnfs_layout_hdr *lo,
>>>>> -                     const nfs4_stateid *stateid)
>>>>> +                     const nfs4_stateid *new)
>>>>>  {
>>>>> -     /* TODO - should enforce that embedded seqid, in the case
>>>>> -      * that the two stateid.others are equal,  only increases.
>>>>> -      * Complicated by wrap-around.
>>>>> -      */
>>>>> +     nfs4_stateid *old = &lo->stateid;
>>>>> +     bool overwrite = false;
>>>>> +
>>>>>       write_seqlock(&lo->seqlock);
>>>>> -     memcpy(lo->stateid.data, stateid->data, sizeof(lo->stateid.data));
>>>>> +     if (!test_bit(NFS_LAYOUT_STATEID_SET, &lo->state) ||
>>>>> +         memcmp(old->stateid.other, new->stateid.other, sizeof(new->stateid.other)))

here we check the 'other' part.

>>>>> +             overwrite = true;
>>>>> +     else {
>>>>> +             u32 oldseq, newseq, limit;
>>>>> +
>>>>> +             oldseq = be32_to_cpu(old->stateid.seqid);
>>>>> +             newseq = be32_to_cpu(new->stateid.seqid);
>>>>> +             /* There are no good bounds on window size, so just
>>>>> +              * use a ridiculously large window of 2^31.
>>>>> +              */
>>>>> +             limit = oldseq + (1 << 31);
>>>>> +             if (oldseq < limit) {
>>>>> +                     /* The easy, non-wraparound case */
>>>>> +                     if (oldseq < newseq && newseq < limit)
>>>>> +                             overwrite = true;
>>>>> +             } else {
>>>>> +                     /* Near wraparound edge */
>>>>> +                     if (oldseq < newseq || newseq < limit)
>>>>> +                             overwrite = true;
>>>>> +             }
>>>>
>>>> Wouldn't it be simpler to just look at (int32_t)(newseq - oldseq)?
>>>>
>>>
>>> Why yes it would.  I'll send a new version of this patch shortly.
>>>
>>
>> No need :)
>> I'll just change this as follows:
>>
>> +       else {
>> +               u32 oldseq, newseq, limit;
>> +
>> +               oldseq = be32_to_cpu(old->stateid.seqid);
>> +               newseq = be32_to_cpu(new->stateid.seqid);
>> +               if ((int)(newseq - oldseq) > 0)
>> +                       overwrite = true;
> Do we also need to verify the other field of the stateid? Will there
> be situations that server change the other field and reset the seqid?

We do :)
see block above.

Benny

> 
> Thanks,
> Shelley
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