Re: [PATCH 1/6] nfs: "open code" the NFS direct write rescheduler

Chuck Lever
2006-05-19T18:37:04Z

Andrew Morton wrote:
> Chuck Lever <cel@netapp.com> wrote:
>> + * Prevent I/O completion while we're still rescheduling
>> + */
>> + dreq->outstanding++;
>> +
>
> No locking.
>
>> dreq->count = 0;
>> + list_for_each(pos, &dreq->rewrite_list) {
>> + struct nfs_write_data *data =
>> + list_entry(dreq->rewrite_list.next, struct nfs_write_data, pages);
>> +
>> + spin_lock(&dreq->lock);
>> + dreq->outstanding++;
>> + spin_unlock(&dreq->lock);
>
> Locking.
>
> Deliberate?

Yes. At the top of the loop, there is no outstanding I/O, so no locking
is needed while updating "outstanding." Inside the loop, we've
dispatched some I/O against "dreq" so locking is needed to ensure
outstanding is updated properly.

--
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