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module/cpu: don’t use core ID from /proc/stat as array index

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/proc/stat lists CPU usage, in the form:

  cpu ...
  cpu0 ...
  cpu1 ...
  ...
  cpuN ...

where the first line is a summary line. We’ve been using the CPU
numbers from /proc/stat to index into our internal stats array.

This doesn’t work on systems where the core IDs aren’t
consecutive. Examples of such systems are SMT systems with SMT
disabled. Here, /proc/stat may look like this instead:

  cpu ...
  cpu0 ...
  cpu2 ...
  cpu4 ...
  ...

With this patch, we ignore the CPU ID from /proc/stat. Instead, we use
a simple counter that is incremented for each (valid) cpu line found
in /proc/stat. To protect against corrupt /proc/stat content, stop
parsing /proc/stat if the number of parsed CPU lines exceed what we
consider to the be total number of CPUs in the system.

Closes #172
This commit is contained in:
Daniel Eklöf 2022-04-07 13:28:35 +02:00
parent fce2787bdf
commit 62ca06eccb
No known key found for this signature in database
GPG key ID: 5BBD4992C116573F
1 changed files with 26 additions and 18 deletions
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44
modules/cpu.c
View file

@ -64,22 +64,27 @@ get_cpu_nb_cores()
} }
static bool static bool
parse_proc_stat_line(const char *line, int32_t *core, uint32_t *user, uint32_t *nice, uint32_t *system, uint32_t *idle, parse_proc_stat_line(const char *line, uint32_t *user, uint32_t *nice, uint32_t *system, uint32_t *idle,
uint32_t *iowait, uint32_t *irq, uint32_t *softirq, uint32_t *steal, uint32_t *guest, uint32_t *iowait, uint32_t *irq, uint32_t *softirq, uint32_t *steal, uint32_t *guest,
uint32_t *guestnice) uint32_t *guestnice)
{ {
int32_t core_id;
if (line[sizeof("cpu") - 1] == ' ') { if (line[sizeof("cpu") - 1] == ' ') {
int read = sscanf(line, int read = sscanf(
"cpu %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 line,
" %" SCNu32 " %" SCNu32 " %" SCNu32, "cpu %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32
user, nice, system, idle, iowait, irq, softirq, steal, guest, guestnice); " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32,
*core = -1; user, nice, system, idle, iowait, irq, softirq, steal, guest,
guestnice);
return read == 10; return read == 10;
} else { } else {
int read = sscanf(line, int read = sscanf(
"cpu%" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 line,
" %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32, "cpu%" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32
core, user, nice, system, idle, iowait, irq, softirq, steal, guest, guestnice); " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32 " %" SCNu32
" %" SCNu32,
&core_id, user, nice, system, idle, iowait, irq, softirq, steal,
guest, guestnice);
return read == 11; return read == 11;
} }
} }
@ -125,20 +130,23 @@ refresh_cpu_stats(struct cpu_stats *cpu_stats)
return; return;
} }
while ((read = getline(&line, &len, fp)) != -1) { while ((read = getline(&line, &len, fp)) != -1 && core <= nb_cores) {
if (strncmp(line, "cpu", sizeof("cpu") - 1) == 0) { if (strncmp(line, "cpu", sizeof("cpu") - 1) == 0) {
if (!parse_proc_stat_line(line, &core, &user, &nice, &system, &idle, &iowait, &irq, &softirq, &steal, if (!parse_proc_stat_line(
&guest, &guestnice) line, &user, &nice, &system, &idle, &iowait, &irq, &softirq, &steal,
|| core < -1 || core >= (int32_t)nb_cores) { &guest, &guestnice))
{
LOG_ERR("unable to parse /proc/stat line"); LOG_ERR("unable to parse /proc/stat line");
goto exit; goto exit;
} }
cpu_stats->prev_cores_idle[core + 1] = cpu_stats->cur_cores_idle[core + 1]; cpu_stats->prev_cores_idle[core] = cpu_stats->cur_cores_idle[core];
cpu_stats->prev_cores_nidle[core + 1] = cpu_stats->cur_cores_nidle[core + 1]; cpu_stats->prev_cores_nidle[core] = cpu_stats->cur_cores_nidle[core];
cpu_stats->cur_cores_idle[core + 1] = idle + iowait; cpu_stats->cur_cores_idle[core] = idle + iowait;
cpu_stats->cur_cores_nidle[core + 1] = user + nice + system + irq + softirq + steal; cpu_stats->cur_cores_nidle[core] = user + nice + system + irq + softirq + steal;
core++;
} }
} }
exit: exit: