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cpuplugd: adjust to CPU 0 being no longer hotpluggable

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With kernel commit 496bb034f4ff ("s390/smp: disallow CPU hotplug
of CPU 0") it is no longer possible to hotplug CPU 0.

As a side effect, the sysfs handle /sys/devices/system/cpu/cpu0/online
does no longer exist. Since cpuplugd relies on checking all online
handles of all CPUs, this change causes cpuplugd to fail as it
interprets a non existing online file as an indicator that no other CPUs
with higher IDs exist as well. This leads to cpuplugd assuming that
there are no CPUs available.

Instead of checking for the online file, it is preferable to check for
the existence of the parent folder to verify the existence of a CPU.
As a consequence, all other checks for non-existing online files must
now imply that the CPU is online, but not hotpluggable.

Signed-off-by: Tobias Huschle <huschle@linux.ibm.com>
Tested-by: Mete Durlu <meted@linux.ibm.com>
Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
This commit is contained in:
Tobias Huschle
2024-01-16 13:12:45 +01:00
committed by Jan Höppner
parent e984b97db0
commit b5f7ac95d8
1 changed files with 9 additions and 8 deletions
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17
cpuplugd/cpu.c
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@@ -25,7 +25,7 @@ int get_numcpus()
for (i = 0; ; i++) {
/* check whether file exists and is readable */
sprintf(path, "/sys/devices/system/cpu/cpu%d/online", i);
sprintf(path, "/sys/devices/system/cpu/cpu%d", i);
if (access(path, R_OK) == 0)
number++;
else
@@ -45,11 +45,13 @@ int get_num_online_cpus()
int status = 0;
int value_of_onlinefile, rc;
for (i = 0; i <= get_numcpus(); i++) {
for (i = 0; i < get_numcpus(); i++) {
/* check wether file exists and is readable */
sprintf(path, "/sys/devices/system/cpu/cpu%d/online", i);
if (access(path, R_OK) != 0)
if (access(path, R_OK) != 0) {
status++;
continue;
}
filp = fopen(path, "r");
if (!filp)
cpuplugd_exit("Cannot open cpu online file: "
@@ -101,10 +103,8 @@ int hotplug(int cpuid)
cpuid);
return -1;
}
} else {
cpuplugd_error("hotplugging cpu with id %d failed\n", cpuid);
return -1;
}
cpuplugd_debug("cpu with id %d cannot be hotplugged\n", cpuid);
return -1;
}
@@ -135,9 +135,8 @@ int hotunplug(int cpuid)
fclose(filp);
if (state == 0)
return 1;
} else {
cpuplugd_error("unplugging cpu with id %d failed\n", cpuid);
}
cpuplugd_debug("cpu with id %d cannot be hotunplugged\n", cpuid);
return retval;
}
@@ -163,6 +162,8 @@ int is_online(int cpuid)
retval = 0;
}
fclose(filp);
} else {
retval = 1;
}
return retval;
}