From: Andrii Nakryiko andriin@fb.com
commit 783b8f01f5942a786998f5577bd9ff3992f22a1a upstream.
It's quite common on some systems to have more CPUs enlisted as "possible", than there are (and could ever be) present/online CPUs. In such cases, perf_buffer creationg will fail due to inability to create perf event on missing CPU with error like this:
libbpf: failed to open perf buffer event on cpu #16: No such device
This patch fixes the logic of perf_buffer__new() to ignore CPUs that are missing or currently offline. In rare cases where user explicitly listed specific CPUs to connect to, behavior is unchanged: libbpf will try to open perf event buffer on specified CPU(s) anyways.
Fixes: fb84b8224655 ("libbpf: add perf buffer API") Signed-off-by: Andrii Nakryiko andriin@fb.com Signed-off-by: Alexei Starovoitov ast@kernel.org Link: https://lore.kernel.org/bpf/20191212013609.1691168-1-andriin@fb.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- tools/lib/bpf/libbpf.c | 32 +++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-)
--- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -5945,7 +5945,7 @@ struct perf_buffer { size_t mmap_size; struct perf_cpu_buf **cpu_bufs; struct epoll_event *events; - int cpu_cnt; + int cpu_cnt; /* number of allocated CPU buffers */ int epoll_fd; /* perf event FD */ int map_fd; /* BPF_MAP_TYPE_PERF_EVENT_ARRAY BPF map FD */ }; @@ -6079,11 +6079,13 @@ perf_buffer__new_raw(int map_fd, size_t static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt, struct perf_buffer_params *p) { + const char *online_cpus_file = "/sys/devices/system/cpu/online"; struct bpf_map_info map = {}; char msg[STRERR_BUFSIZE]; struct perf_buffer *pb; + bool *online = NULL; __u32 map_info_len; - int err, i; + int err, i, j, n;
if (page_cnt & (page_cnt - 1)) { pr_warn("page count should be power of two, but is %zu\n", @@ -6152,20 +6154,32 @@ static struct perf_buffer *__perf_buffer goto error; }
- for (i = 0; i < pb->cpu_cnt; i++) { + err = parse_cpu_mask_file(online_cpus_file, &online, &n); + if (err) { + pr_warn("failed to get online CPU mask: %d\n", err); + goto error; + } + + for (i = 0, j = 0; i < pb->cpu_cnt; i++) { struct perf_cpu_buf *cpu_buf; int cpu, map_key;
cpu = p->cpu_cnt > 0 ? p->cpus[i] : i; map_key = p->cpu_cnt > 0 ? p->map_keys[i] : i;
+ /* in case user didn't explicitly requested particular CPUs to + * be attached to, skip offline/not present CPUs + */ + if (p->cpu_cnt <= 0 && (cpu >= n || !online[cpu])) + continue; + cpu_buf = perf_buffer__open_cpu_buf(pb, p->attr, cpu, map_key); if (IS_ERR(cpu_buf)) { err = PTR_ERR(cpu_buf); goto error; }
- pb->cpu_bufs[i] = cpu_buf; + pb->cpu_bufs[j] = cpu_buf;
err = bpf_map_update_elem(pb->map_fd, &map_key, &cpu_buf->fd, 0); @@ -6177,21 +6191,25 @@ static struct perf_buffer *__perf_buffer goto error; }
- pb->events[i].events = EPOLLIN; - pb->events[i].data.ptr = cpu_buf; + pb->events[j].events = EPOLLIN; + pb->events[j].data.ptr = cpu_buf; if (epoll_ctl(pb->epoll_fd, EPOLL_CTL_ADD, cpu_buf->fd, - &pb->events[i]) < 0) { + &pb->events[j]) < 0) { err = -errno; pr_warn("failed to epoll_ctl cpu #%d perf FD %d: %s\n", cpu, cpu_buf->fd, libbpf_strerror_r(err, msg, sizeof(msg))); goto error; } + j++; } + pb->cpu_cnt = j; + free(online);
return pb;
error: + free(online); if (pb) perf_buffer__free(pb); return ERR_PTR(err);