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tick/nohz: avoid showing '(null)' if nohz_full= not set

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In the context of CONFIG_NO_HZ_FULL=y, tick_nohz_full_mask (of type
cpumask_var_t) is initialised to 0. Memory is only allocated to the cpumask
data structure, in tick_nohz_full_setup(), when Linux kernel boot-time
parameter "nohz_full=" is correctly specified (see housekeeping_setup()).
If "nohz_full=" is not set and an attempt is made to read
/sys/devices/system/cpu/nohz_full, '(null)' can be displayed:

    ❯ cat /sys/devices/system/cpu/nohz_full
    (null)

This patch changes the output to print a newline (or 0x0A) instead of
'(null)', making it consistent with print_cpus_isolated() behaviour.

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
Link: https://patch.msgid.link/20251011011830.6670-3-atomlin@atomlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Aaron Tomlin
2025-10-10 21:18:30 -04:00
committed by Greg Kroah-Hartman
parent 76987bac71
commit f10c23fa15
1 changed files with 4 additions and 1 deletions
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5
drivers/base/cpu.c
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@@ -305,7 +305,10 @@ static ssize_t nohz_full_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(tick_nohz_full_mask));
if (cpumask_available(tick_nohz_full_mask))
return sysfs_emit(buf, "%*pbl\n",
cpumask_pr_args(tick_nohz_full_mask));
return sysfs_emit(buf, "\n");
}
static DEVICE_ATTR_RO(nohz_full);
#endif