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libbpf: Auto-bump RLIMIT_MEMLOCK if kernel needs it for BPF

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The need to increase RLIMIT_MEMLOCK to do anything useful with BPF is
one of the first extremely frustrating gotchas that all new BPF users go
through and in some cases have to learn it a very hard way.

Luckily, starting with upstream Linux kernel version 5.11, BPF subsystem
dropped the dependency on memlock and uses memcg-based memory accounting
instead. Unfortunately, detecting memcg-based BPF memory accounting is
far from trivial (as can be evidenced by this patch), so in practice
most BPF applications still do unconditional RLIMIT_MEMLOCK increase.

As we move towards libbpf 1.0, it would be good to allow users to forget
about RLIMIT_MEMLOCK vs memcg and let libbpf do the sensible adjustment
automatically. This patch paves the way forward in this matter. Libbpf
will do feature detection of memcg-based accounting, and if detected,
will do nothing. But if the kernel is too old, just like BCC, libbpf
will automatically increase RLIMIT_MEMLOCK on behalf of user
application ([0]).

As this is technically a breaking change, during the transition period
applications have to opt into libbpf 1.0 mode by setting
LIBBPF_STRICT_AUTO_RLIMIT_MEMLOCK bit when calling
libbpf_set_strict_mode().

Libbpf allows to control the exact amount of set RLIMIT_MEMLOCK limit
with libbpf_set_memlock_rlim_max() API. Passing 0 will make libbpf do
nothing with RLIMIT_MEMLOCK. libbpf_set_memlock_rlim_max() has to be
called before the first bpf_prog_load(), bpf_btf_load(), or
bpf_object__load() call, otherwise it has no effect and will return
-EBUSY.

  [0] Closes: https://github.com/libbpf/libbpf/issues/369

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211214195904.1785155-2-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko
2021-12-14 11:59:03 -08:00
committed by Daniel Borkmann
parent 9fc205b413
commit e542f2c4cd
6 changed files with 143 additions and 39 deletions
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47
tools/lib/bpf/libbpf.c
View File

@@ -187,42 +187,6 @@ const char *libbpf_version_string(void)
#undef __S
}
enum kern_feature_id {
/* v4.14: kernel support for program & map names. */
FEAT_PROG_NAME,
/* v5.2: kernel support for global data sections. */
FEAT_GLOBAL_DATA,
/* BTF support */
FEAT_BTF,
/* BTF_KIND_FUNC and BTF_KIND_FUNC_PROTO support */
FEAT_BTF_FUNC,
/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
FEAT_BTF_DATASEC,
/* BTF_FUNC_GLOBAL is supported */
FEAT_BTF_GLOBAL_FUNC,
/* BPF_F_MMAPABLE is supported for arrays */
FEAT_ARRAY_MMAP,
/* kernel support for expected_attach_type in BPF_PROG_LOAD */
FEAT_EXP_ATTACH_TYPE,
/* bpf_probe_read_{kernel,user}[_str] helpers */
FEAT_PROBE_READ_KERN,
/* BPF_PROG_BIND_MAP is supported */
FEAT_PROG_BIND_MAP,
/* Kernel support for module BTFs */
FEAT_MODULE_BTF,
/* BTF_KIND_FLOAT support */
FEAT_BTF_FLOAT,
/* BPF perf link support */
FEAT_PERF_LINK,
/* BTF_KIND_DECL_TAG support */
FEAT_BTF_DECL_TAG,
/* BTF_KIND_TYPE_TAG support */
FEAT_BTF_TYPE_TAG,
__FEAT_CNT,
};
static bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id);
enum reloc_type {
RELO_LD64,
RELO_CALL,
@@ -4352,6 +4316,10 @@ bpf_object__probe_loading(struct bpf_object *obj)
if (obj->gen_loader)
return 0;
ret = bump_rlimit_memlock();
if (ret)
pr_warn("Failed to bump RLIMIT_MEMLOCK (err = %d), you might need to do it explicitly!\n", ret);
/* make sure basic loading works */
ret = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL", insns, insn_cnt, NULL);
if (ret < 0)
@@ -4718,14 +4686,17 @@ static struct kern_feature_desc {
[FEAT_BTF_TYPE_TAG] = {
"BTF_KIND_TYPE_TAG support", probe_kern_btf_type_tag,
},
[FEAT_MEMCG_ACCOUNT] = {
"memcg-based memory accounting", probe_memcg_account,
},
};
static bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
{
struct kern_feature_desc *feat = &feature_probes[feat_id];
int ret;
if (obj->gen_loader)
if (obj && obj->gen_loader)
/* To generate loader program assume the latest kernel
* to avoid doing extra prog_load, map_create syscalls.
*/