On 9/24/20 8:21 PM, Daniel Borkmann wrote:
> With its use in BPF the cookie generator can be called very frequently
> in particular when used out of cgroup v2 hooks (e.g. connect / sendmsg)
> and attached to the root cgroup, for example, when used in v1/v2 mixed
> environments. In particular when there's a high churn on sockets in the
> system there can be many parallel requests to the bpf_get_socket_cookie()
> and bpf_get_netns_cookie() helpers which then cause contention on the
> shared atomic counter. As similarly done in f991bd2e1421 ("fs: introduce
> a per-cpu last_ino allocator"), add a small helper library that both can
> then use for the 64 bit counters.
>
> Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
> ---
> include/linux/cookie.h | 41 ++++++++++++++++++++++++++++++++++++++++
> net/core/net_namespace.c | 5 +++--
> net/core/sock_diag.c | 7 ++++---
> 3 files changed, 48 insertions(+), 5 deletions(-)
> create mode 100644 include/linux/cookie.h
>
> diff --git a/include/linux/cookie.h b/include/linux/cookie.h
> new file mode 100644
> index 000000000000..2488203dc004
> --- /dev/null
> +++ b/include/linux/cookie.h
> @@ -0,0 +1,41 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __LINUX_COOKIE_H
> +#define __LINUX_COOKIE_H
> +
> +#include <linux/atomic.h>
> +#include <linux/percpu.h>
> +
> +struct gen_cookie {
> + u64 __percpu *local_last;
> + atomic64_t shared_last ____cacheline_aligned_in_smp;
> +};
> +
> +#define COOKIE_LOCAL_BATCH 4096
> +
> +#define DEFINE_COOKIE(name) \
> + static DEFINE_PER_CPU(u64, __##name); \
> + static struct gen_cookie name = { \
> + .local_last = &__##name, \
> + .shared_last = ATOMIC64_INIT(0), \
> + }
> +
> +static inline u64 gen_cookie_next(struct gen_cookie *gc)
> +{
> + u64 *local_last = &get_cpu_var(*gc->local_last);
> + u64 val = *local_last;
> +
> + if (__is_defined(CONFIG_SMP) &&
> + unlikely((val & (COOKIE_LOCAL_BATCH - 1)) == 0)) {
> + s64 next = atomic64_add_return(COOKIE_LOCAL_BATCH,
> + &gc->shared_last);
> + val = next - COOKIE_LOCAL_BATCH;
> + }
> + val++;
> + if (unlikely(!val))
> + val++;
> + *local_last = val;
> + put_cpu_var(local_last);
> + return val;
This is not interrupt safe.
I think sock_gen_cookie() can be called from interrupt context.
get_next_ino() is only called from process context, that is what I used
get_cpu_var()
and put_cpu_var()
