[PATCH v2 1/2] powercap: dtpm_cpu: Guard em_cpu_get() against NULL return in sysfs callbacks

[sivany32@gmail.com]

From: Sivan Zohar-Kotzer <sivany32@gmail.com>

em_cpu_get() can return NULL when a CPU becomes impossible. Two call
sites miss the NULL test:

1. set_pd_power_limit() — reachable from sysfs via the powercap
   constraint power_limit_uw store path. If the CPU has become
   impossible then pd will be NULL, return the current power limit
   unchanged (no-op) instead of crashing.

2. update_pd_power_uw() — called from CPU hotplug handlers via
   dtpm_update_power(). While reaching this with a NULL em may be
   technically impossible today, the check is kept for defense in
   depth against future refactoring or subtle races.

The other sysfs-reachable path, get_pd_power_uw(), already has a NULL
guard returning 0.

Fixes: 0e8f68d7f048 ("powercap/drivers/dtpm: Add CPU energy model based support")
Signed-off-by: Sivan Zohar-Kotzer <sivany32@gmail.com>
Co-developed-by: Elazar Leibovich <elazarl@gmail.com>
Signed-off-by: Elazar Leibovich <elazarl@gmail.com>
---
 drivers/powercap/dtpm_cpu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
index 21355db64..886cbe922 100644
--- a/drivers/powercap/dtpm_cpu.c
+++ b/drivers/powercap/dtpm_cpu.c
@@ -47,6 +47,9 @@ static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit)
 	u64 power;
 	int i, nr_cpus;
 
+	if (!pd)
+		return dtpm->power_limit;
+
 	nr_cpus = cpumask_weight_and(cpu_online_mask, to_cpumask(pd->cpus));
 
 	rcu_read_lock();
@@ -125,6 +128,9 @@ static int update_pd_power_uw(struct dtpm *dtpm)
 	struct em_perf_state *table;
 	int nr_cpus;
 
+	if (!em)
+		return -EINVAL;
+
 	nr_cpus = cpumask_weight_and(cpu_online_mask, to_cpumask(em->cpus));
 
 	rcu_read_lock();
-- 
2.39.5 (Apple Git-154)