Having static variable `cpus` in libbpf_num_possible_cpus function without
guarding it with mutex makes this function thread-unsafe.
If multiple threads accessing this function, in the current form; it
leads to incrementing the static variable value `cpus` in the multiple
of total available CPUs.
Let caching the number of possile CPUs handled by libbpf's users than
this library itself; and let this function be rock bottom one which reads
and parse the file (/sys/devices/system/cpu/possible) everytime it gets
called to simplify the things.
Fixes: 6446b3155521 (bpf: add a new API libbpf_num_possible_cpus())
Signed-off-by: Takshak Chahande <ctaks...@fb.com>
Acked-by: Andrey Ignatov <r...@fb.com>
---
tools/lib/bpf/libbpf.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index ead915aec349..e7ac0e02287e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4998,14 +4998,11 @@ int libbpf_num_possible_cpus(void)
static const char *fcpu = "/sys/devices/system/cpu/possible";
int len = 0, n = 0, il = 0, ir = 0;
unsigned int start = 0, end = 0;
- static int cpus;
char buf[128];
int error = 0;
+ int cpus = 0;
int fd = -1;
- if (cpus > 0)
- return cpus;
-
fd = open(fcpu, O_RDONLY);
if (fd < 0) {
error = errno;
--
2.17.1
