arm_mpam: Fix false positive assert failure during mpam_disable()

mpam_assert_partid_sizes_fixed() is used to document that the caller
doesn't expect the discovered PARTID size to change while it is walking
a list sized by PARTID. Typically the MSC state is not written to until
all the MSC have been discovered and this value is set.

However, if discovering the MSC fails and schedules mpam_disable(),
then the MSC state is written to reset it. In this case the
discovered PARTID size may be become smaller - but only PARTID 0
will be used once resctrl_exit() has been called.

Skip the WARN_ON_ONCE() if mpam_disable_reason has been set.

Fixes: 3bd04fe7d807 ("arm_mpam: Extend reset logic to allow devices to be reset any time")
Cc: <stable@vger.kernel.org>
Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index e145828f3f736b138cde5665f66ee9cb48ec0add..5c48812d8573b5fe8dabfef883d809b9380bf2cf 100644 (file)
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -164,11 +164,17 @@ static void mpam_free_garbage(void)
 /*
  * Once mpam is enabled, new requestors cannot further reduce the available
  * partid. Assert that the size is fixed, and new requestors will be turned
- * away.
+ * away. This is needed when walking over structures sized by PARTID.
+ *
+ * During mpam_disable() these structures are not fixed, but the MSC state
+ * is still reset using whatever sizes have been discovered so far. As only
+ * PARTID 0 will be used after mpam_disable(), any race would be benign.
+ * Skip the check if a mpam_disable_reason has been set.
  */
 static void mpam_assert_partid_sizes_fixed(void)
 {
-       WARN_ON_ONCE(!partid_max_published);
+       if (!mpam_disable_reason)
+               WARN_ON_ONCE(!partid_max_published);
 }
 
 static u32 __mpam_read_reg(struct mpam_msc *msc, u16 reg)