[PATCH] accel/rocket: search every core slot when a core is removed

[Igor Paunovic <royalnet026@gmail.com>]

rocket_remove() decrements rdev->num_cores for each core it removes,
while find_core_for_dev() searches slots 0 to num_cores - 1. Unbinding
the cores in the order they were bound therefore loses the last one: by
the time it is removed the search range has already shrunk past its
slot, so find_core_for_dev() returns -1 and rocket_remove() gives up
without doing anything.

num_cores never reaches zero, rocket_device_fini() never runs, and the
file-scoped rdev keeps pointing at a device that is going away. Binding
the cores again starts from that stale count, because rocket_probe()
takes rdev->num_cores as the slot to fill. On an RK3588, which describes
three cores, the second round lands on slots 1, 2 and 3 while rdev->cores
was allocated with room for three:

  rocket fdab0000.npu: Rockchip NPU core 1 version: 1179210309
  rocket fdac0000.npu: Rockchip NPU core 2 version: 1179210309
  rocket fdad0000.npu: Rockchip NPU core 3 version: 1179210309

The write to rdev->cores[3] is past the end of the array.

Nothing in tree reads the core array often enough to notice, so the
overrun is silent today. It turned up while testing a devfreq series on
top of this, where a worker walks every core a few times a second, and
UBSAN caught the first bool it read out of the overrun entry:

  UBSAN: invalid-load in drivers/accel/rocket/rocket_devfreq.c:47:10
  load of value 5 is not a valid value for type '_Bool'
  Workqueue: devfreq_wq devfreq_monitor

Record how many slots were allocated and search all of them. Every core
is then found on removal, num_cores reaches zero, the device is torn down
and a later bind starts from a clean rdev.

This does not make unbinding a single core out of several work. probe
still takes num_cores as the slot to fill, so rebinding one core while
its siblings stay bound would write over a slot that is already in use,
and rocket_open() still reaches for cores[0] whether or not anything is
there. Both of those want more thought than a fix should carry.

Found by unbinding and rebinding all three cores on an Orange Pi 5 Plus.
With this applied, 25 unbind/rebind rounds and 5 module unload/reload
rounds run clean there: the cores land in slots 0, 1 and 2 every time,
whichever order they are bound in, and the shared supply goes back to a
single user after each round.

Fixes: ed98261b4168 ("accel/rocket: Add a new driver for Rockchip's NPU")
Cc: stable@vger.kernel.org
Signed-off-by: Igor Paunovic <royalnet026@gmail.com>
Assisted-by: LLM sparse checkpatch
---
 drivers/accel/rocket/rocket_device.c | 2 ++
 drivers/accel/rocket/rocket_device.h | 1 +
 drivers/accel/rocket/rocket_drv.c    | 2 +-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/accel/rocket/rocket_device.c b/drivers/accel/rocket/rocket_device.c
index 46e6ee1e72c5f..efd004194c1af 100644
--- a/drivers/accel/rocket/rocket_device.c
+++ b/drivers/accel/rocket/rocket_device.c
@@ -31,6 +31,8 @@ struct rocket_device *rocket_device_init(struct platform_device *pdev,
 		if (of_device_is_available(core_node))
 			num_cores++;
 
+	rdev->max_cores = num_cores;
+
 	rdev->cores = devm_kcalloc(dev, num_cores, sizeof(*rdev->cores), GFP_KERNEL);
 	if (!rdev->cores)
 		return ERR_PTR(-ENOMEM);
diff --git a/drivers/accel/rocket/rocket_device.h b/drivers/accel/rocket/rocket_device.h
index ce662abc01d3d..c62d567010696 100644
--- a/drivers/accel/rocket/rocket_device.h
+++ b/drivers/accel/rocket/rocket_device.h
@@ -19,6 +19,7 @@ struct rocket_device {
 
 	struct rocket_core *cores;
 	unsigned int num_cores;
+	unsigned int max_cores;
 };
 
 struct rocket_device *rocket_device_init(struct platform_device *pdev,
diff --git a/drivers/accel/rocket/rocket_drv.c b/drivers/accel/rocket/rocket_drv.c
index 8bbbce594883e..2bcfe4ab3c68f 100644
--- a/drivers/accel/rocket/rocket_drv.c
+++ b/drivers/accel/rocket/rocket_drv.c
@@ -223,7 +223,7 @@ static int find_core_for_dev(struct device *dev)
 {
 	struct rocket_device *rdev = dev_get_drvdata(dev);
 
-	for (unsigned int core = 0; core < rdev->num_cores; core++) {
+	for (unsigned int core = 0; core < rdev->max_cores; core++) {
 		if (dev == rdev->cores[core].dev)
 			return core;
 	}
-- 
2.43.0