Re: [dpdk-stable] [PATCH] mempool: fix mempool virt populate with small chunks

[Olivier Matz <olivier.matz@6wind.com>]

On Thu, Jan 09, 2020 at 01:52:41PM +0000, Burakov, Anatoly wrote:
> On 09-Jan-20 1:27 PM, Olivier Matz wrote:
> > To populate a mempool with a virtual area, the mempool code calls
> > rte_mempool_populate_iova() for each iova-contiguous area. It happens
> > (rarely) that this area is too small to store one object. In this case,
> > rte_mempool_populate_iova() returns an error, which is forwarded by
> > rte_mempool_populate_virt().
> > 
> > This case should not throw an error in
> > rte_mempool_populate_virt(). Instead, the area that is too small should
> > just be ignored.
> > 
> > To fix this issue, change the return value of
> > rte_mempool_populate_iova() to -ENOBUFS when no object can be populated,
> > so it can be ignored by the caller. As this would be an API change, add
> > a compat wrapper to keep the current API unchanged. The wrapper will be
> > removed for 20.11.
> > 
> > Fixes: 354788b60cfd ("mempool: allow populating with unaligned virtual area")
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> > ---
> > 
> 
> The approach fixes the issue on my end, so
> 
> Tested-by: Anatoly Burakov <anatoly.burakov@intel.com>
> 
> > Is there a simple way to ensure that we won't forget to remove the
> > wrapper for 20.11? Anatoly suggested me to use versioned symbols, but
> > it's not clear to me how.
> > 
> 
> Yes, i'd like to do better than "ah shur we won't forget pinky swear".
> 
> Can't we do this with ABI versioning? E.g.
> 
> rte_populate_iova_v20() ... returns EINVAL
> 
> rte_populate_iova_v21() ... returns ENOBUFS
> 
> I'm pretty sure, even if it doesn't break, it will still be more likely to
> not be forgotten because there's almost a guarantee that someone will grep
> for symbol versioning macros across the codebase around 20.11 timeframe.

Without using symbol versionning, would this be ok too?

  int
  rte_mempool_populate_iova(struct rte_mempool *mp, char *vaddr,
         rte_iova_t iova, size_t len, rte_mempool_memchunk_free_cb_t *free_cb,
         void *opaque)
  {
         int ret;

         ret = __rte_mempool_populate_iova(mp, vaddr, iova, len, free_cb, opaque);

  #if RTE_VERSION < RTE_VERSION_NUM(20, 11, 0, 0)
         if (ret == -ENOBUFS)
                 ret = -EINVAL;
  #endif

         return ret;
  }



> -- 
> Thanks,
> Anatoly