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Message-ID: <20251006005824.76187-1-atomlin@atomlin.com>
Date: Sun, 5 Oct 2025 20:58:24 -0400
From: Aaron Tomlin <atomlin@...mlin.com>
To: gregkh@...uxfoundation.org,
rafael@...nel.org,
dakr@...nel.org
Cc: riel@...riel.com,
frederic@...nel.org,
atomlin@...mlin.com,
linux-kernel@...r.kernel.org
Subject: [PATCH] tick/nohz: avoid showing '(null)' if nohz_full= not set
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@...mlin.com>
---
drivers/base/cpu.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index fa0a2eef93ac..f694b4b24d6c 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -304,7 +304,9 @@ static DEVICE_ATTR(isolated, 0444, print_cpus_isolated, NULL);
static ssize_t print_cpus_nohz_full(struct device *dev,
struct device_attribute *attr, char *buf)
{
- return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(tick_nohz_full_mask));
+ return !tick_nohz_full_mask ?
+ sysfs_emit(buf, "\n") :
+ sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(tick_nohz_full_mask));
}
static DEVICE_ATTR(nohz_full, 0444, print_cpus_nohz_full, NULL);
#endif
--
2.49.0
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