Re: [PATCH v16 06/12] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

On Tue, 2022-09-06 at 11:45 -0700, Alexei Starovoitov wrote:

On Tue, Sep 6, 2022 at 1:01 AM Roberto Sassu roberto.sassu@huaweicloud.com wrote:

...

...

...

+struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) +{

•   key_ref_t key_ref;
  

•   struct bpf_key *bkey;
  

•   if (flags & ~KEY_LOOKUP_ALL)
  

•           return NULL;
  

•   /*
  

•    * Permission check is deferred until the key is used,
  

as the

•    * intent of the caller is unknown here.
  

•    */
  

•   key_ref = lookup_user_key(serial, flags,
  

KEY_DEFER_PERM_CHECK);

•   if (IS_ERR(key_ref))
  

•           return NULL;
  

•   bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC);
  

Since this function (due to lookup_user_key) is sleepable, do we really need GFP_ATOMIC here?

Daniel suggested it for bpf_lookup_system_key(), so that the kfunc does not have to be sleepable.

Hold on. It has to be sleepable. Just take a look at what lookup_user_key is doing inside.

https://lore.kernel.org/bpf/2b1d62ad-af4b-4694-ecc8-639fbd821a05@iogearbox.n...

Roberto