[PATCH v3 1/5] irqchip/mips-gic: Fix unbalanced cm_core_lock in for_each_online_cpu_gic()

["Benoît Monin" <benoit.monin@bootlin.com>]

Commit d9e2ed610a60 ("irqchip/mips-gic: Support multi-cluster in
for_each_online_cpu_gic()") added a gic_unlock_cluster() call to the
macro's loop increment, which unconditionally invokes
mips_cm_unlock_other() on multi-cluster systems. However nothing in the
loop ever acquires the corresponding mips_cm_lock_other(), so on
multi-cluster hardware every invocation of for_each_online_cpu_gic()
releases an unheld per-CPU cm_core_lock.

With CONFIG_PROVE_LOCKING this triggers a "bad unlock balance detected"
warning at boot, e.g. from gic_irq_domain_map() while mapping local
interrupts. Only the first occurrence is reported, since the first
warning permanently disables lockdep (debug_locks = 0); the unbalanced
release itself silently persists.

Fix this by moving both the acquire and release into
__gic_with_next_online_cpu() so they stay balanced. When advancing to a
CPU in a remote cluster, lock the CM redirect block for that cluster via
mips_cm_lock_other(); when leaving a remote cluster (or finishing the
iteration) release it with mips_cm_unlock_other(). Local-cluster CPUs
require no locking, so single-cluster systems are unaffected. This also
makes the redirect region behave correctly when accessing local register
blocks of CPUs in other clusters.

Drop the now-unused gic_unlock_cluster() helper and its call from the
for_each_online_cpu_gic() increment.

Fixes: d9e2ed610a60 ("irqchip/mips-gic: Support multi-cluster in for_each_online_cpu_gic()")
Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>
---
 drivers/irqchip/irq-mips-gic.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/drivers/irqchip/irq-mips-gic.c b/drivers/irqchip/irq-mips-gic.c
index 19a57c5e2b2e..3b31cbcbed6f 100644
--- a/drivers/irqchip/irq-mips-gic.c
+++ b/drivers/irqchip/irq-mips-gic.c
@@ -70,6 +70,10 @@ static int __gic_with_next_online_cpu(int prev)
 {
 	unsigned int cpu;
 
+	/* Release the redirect/other region lock to the previous CPU, if any. */
+	if (prev >= 0)
+		mips_cm_unlock_other();
+
 	/* Discover the next online CPU */
 	cpu = cpumask_next(prev, cpu_online_mask);
 
@@ -77,23 +81,12 @@ static int __gic_with_next_online_cpu(int prev)
 	if (cpu >= nr_cpu_ids)
 		return cpu;
 
-	/*
-	 * Move the access lock to the next CPU's GIC local register block.
-	 *
-	 * Set GIC_VL_OTHER. Since the caller holds gic_lock nothing can
-	 * clobber the written value.
-	 */
-	write_gic_vl_other(mips_cm_vp_id(cpu));
+	/* Lock access to redirect/other region to the next CPU */
+	mips_cm_lock_other_cpu(cpu, CM_GCR_Cx_OTHER_BLOCK_LOCAL);
 
 	return cpu;
 }
 
-static inline void gic_unlock_cluster(void)
-{
-	if (mips_cps_multicluster_cpus())
-		mips_cm_unlock_other();
-}
-
 /**
  * for_each_online_cpu_gic() - Iterate over online CPUs, access local registers
  * @cpu: An integer variable to hold the current CPU number
@@ -108,7 +101,6 @@ static inline void gic_unlock_cluster(void)
 	guard(raw_spinlock_irqsave)(gic_lock);		\
 	for ((cpu) = __gic_with_next_online_cpu(-1);	\
 	     (cpu) < nr_cpu_ids;			\
-	     gic_unlock_cluster(),			\
 	     (cpu) = __gic_with_next_online_cpu(cpu))
 
 /**

-- 
2.55.0