[PATCH RFC 12/15] arm_mpam: Fix get_cpumask_from_cache() to clear mask on error

[Yin Li]

If mpam_get_cpumask_from_cache_id() fails, the affinity mask may have
been partially filled before the error occurred. The caller has no way
to distinguish a partial mask from a valid one, so it may misuse the
incomplete result.

Clear the affinity mask before returning the error so the caller always
receives either a fully valid mask or an empty one.

Co-developed-by: Huang Yiwei <huang.yiwei@xxxxxxxxxxxxxxxx>
Signed-off-by: Huang Yiwei <huang.yiwei@xxxxxxxxxxxxxxxx>
Signed-off-by: Yin Li <yin.li@xxxxxxxxxxxxxxxx>
---
 drivers/resctrl/mpam_devices.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index eac3bc695fd1..d8856864e89a 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -243,7 +243,12 @@ static int get_cpumask_from_cache(struct device_node *cache,
 		return -ENOENT;
 	}
 
-	return mpam_get_cpumask_from_cache_id(cache_id, cache_level, affinity);
+	err = mpam_get_cpumask_from_cache_id(cache_id, cache_level, affinity);
+	if (err)
+		/* Don't leave a partially-filled mask for the caller to misuse */
+		cpumask_clear(affinity);
+
+	return err;
 }
 
 static int mpam_dt_count_msc(void)

-- 
2.34.1