From e542f2c4cd16d49392abf3349341d58153d3c603 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Tue, 14 Dec 2021 11:59:03 -0800 Subject: libbpf: Auto-bump RLIMIT_MEMLOCK if kernel needs it for BPF 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 Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20211214195904.1785155-2-andrii@kernel.org --- tools/lib/bpf/libbpf.c | 47 +++++++++-------------------------------------- 1 file changed, 9 insertions(+), 38 deletions(-) (limited to 'tools/lib/bpf/libbpf.c') diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index c6d84b01a59e..684c34ce1a26 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -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. */ -- cgit v1.2.3