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Date: Mon, 28 Sep 2020 18:48:54 -0700 (PDT) From: David Miller <davem@...emloft.net> To: gustavoars@...nel.org Cc: jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us, kuba@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, keescook@...omium.org Subject: Re: [PATCH][next] net/sched: cls_u32: Replace one-element array with flexible-array member From: "Gustavo A. R. Silva" <gustavoars@...nel.org> Date: Mon, 28 Sep 2020 10:30:52 -0500 > There is a regular need in the kernel to provide a way to declare having > a dynamically sized set of trailing elements in a structure. Kernel code > should always use “flexible array members”[1] for these cases. The older > style of one-element or zero-length arrays should no longer be used[2]. > > Refactor the code according to the use of a flexible-array member in > struct tc_u_hnode and use the struct_size() helper to calculate the > size for the allocations. Commit 5778d39d070b ("net_sched: fix struct > tc_u_hnode layout in u32") makes it clear that the code is expected to > dynamically allocate divisor + 1 entries for ->ht[] in tc_uhnode. Also, > based on other observations, as the piece of code below: > > 1232 for (h = 0; h <= ht->divisor; h++) { > 1233 for (n = rtnl_dereference(ht->ht[h]); > 1234 n; > 1235 n = rtnl_dereference(n->next)) { > 1236 if (tc_skip_hw(n->flags)) > 1237 continue; > 1238 > 1239 err = u32_reoffload_knode(tp, n, add, cb, > 1240 cb_priv, extack); > 1241 if (err) > 1242 return err; > 1243 } > 1244 } > > we can assume that, in general, the code is actually expecting to allocate > that extra space for the one-element array in tc_uhnode, everytime it > allocates memory for instances of tc_uhnode or tc_u_common structures. > That's the reason for passing '1' as the last argument for struct_size() > in the allocation for _root_ht_ and _tp_c_, and 'divisor + 1' in the > allocation code for _ht_. > > [1] https://en.wikipedia.org/wiki/Flexible_array_member > [2] https://www.kernel.org/doc/html/v5.9-rc1/process/deprecated.html#zero-length-and-one-element-arrays > > Tested-by: kernel test robot <lkp@...el.com> > Link: https://lore.kernel.org/lkml/5f7062af.z3T9tn9yIPv6h5Ny%25lkp@intel.com/ > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org> Applied.
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