Re: [PATCH v7 01/22] net/tcp: Prepare tcp_md5sig_pool for TCP-AO

[Steen Hegelund]

Hi Dmitry,

On Thu, 2023-06-15 at 00:09 +0100, Dmitry Safonov wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the
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> 
> TCP-AO, similarly to TCP-MD5, needs to allocate tfms on a slow-path,
> which is setsockopt() and use crypto ahash requests on fast paths,
> which are RX/TX softirqs. Also, it needs a temporary/scratch buffer
> for preparing the hash.
> 
> Rework tcp_md5sig_pool in order to support other hashing algorithms
> than MD5. It will make it possible to share pre-allocated crypto_ahash
> descriptors and scratch area between all TCP hash users.
> 
> Internally tcp_sigpool calls crypto_clone_ahash() API over pre-allocated
> crypto ahash tfm. Kudos to Herbert, who provided this new crypto API.
> 
> I was a little concerned over GFP_ATOMIC allocations of ahash and
> crypto_request in RX/TX (see tcp_sigpool_start()), so I benchmarked both
> "backends" with different algorithms, using patched version of iperf3[2].
> On my laptop with i7-7600U @ 2.80GHz:
> 

... snip ...

> +/**
> + * tcp_sigpool_alloc_ahash - allocates pool for ahash requests
> + * @alg: name of async hash algorithm
> + * @scratch_size: reserve a tcp_sigpool::scratch buffer of this size
> + */
> +int tcp_sigpool_alloc_ahash(const char *alg, size_t scratch_size)
> +{
> +       int i, ret;
> +
> +       /* slow-path */
> +       mutex_lock(&cpool_mutex);
> +       ret = sigpool_reserve_scratch(scratch_size);
> +       if (ret)
> +               goto out;
> +       for (i = 0; i < cpool_populated; i++) {
> +               if (!cpool[i].alg)
> +                       continue;
> +               if (strcmp(cpool[i].alg, alg))
> +                       continue;
> +
> +               if (kref_read(&cpool[i].kref) > 0)
> +                       kref_get(&cpool[i].kref);
> +               else
> +                       kref_init(&cpool[i].kref);
> +               ret = i;
> +               goto out;
> +       }

Here it looks to me like you will never get to this part of the code since you
always end up going to the out label in the previous loop.

> +
> +       for (i = 0; i < cpool_populated; i++) {
> +               if (!cpool[i].alg)
> +                       break;
> +       }
> +       if (i >= CPOOL_SIZE) {
> +               ret = -ENOSPC;
> +               goto out;
> +       }
> +
> +       ret = __cpool_alloc_ahash(&cpool[i], alg);
> +       if (!ret) {
> +               ret = i;
> +               if (i == cpool_populated)
> +                       cpool_populated++;
> +       }
> +out:
> +       mutex_unlock(&cpool_mutex);
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(tcp_sigpool_alloc_ahash);
> +

... snip ...


>  clear_hash:
> -       tcp_put_md5sig_pool();
> -clear_hash_noput:
> +       tcp_sigpool_end(&hp);
> +clear_hash_nostart:
>         memset(md5_hash, 0, 16);
>         return 1;
>  }
> --
> 2.40.0
> 
> 

BR
Steen