[PATCH v7 01/10] accel/rocket: take the completion register writes under job_lock

[Jiaxing Hu <gahing@gahingwoo.com>]

rocket_job_handle_irq() writes OPERATION_ENABLE and INTERRUPT_CLEAR before
taking job_lock, while rocket_job_hw_submit() writes OPERATION_ENABLE from
inside it. The two can therefore race: a completion being handled on one core
can write its zero after a submit on the same core has written its one, and
stop a task that has only just started.

Nothing in tree hits this often, because the interrupt is the only completion
path and it does not overlap its own submit, but the ordering is wrong on its
own terms.

Move both writes inside the existing scoped_guard() rather than adding a second
critical section, so stopping the block and deciding what to start next are one
atomic step.

Fixes: 0810d5ad88a1 ("accel/rocket: Add job submission IOCTL")
Signed-off-by: Jiaxing Hu <gahing@gahingwoo.com>
---
 drivers/accel/rocket/rocket_job.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/accel/rocket/rocket_job.c b/drivers/accel/rocket/rocket_job.c
index bb77b6bf0..4c01b703e 100644
--- a/drivers/accel/rocket/rocket_job.c
+++ b/drivers/accel/rocket/rocket_job.c
@@ -345,10 +345,15 @@ static void rocket_job_handle_irq(struct rocket_core *core)
 {
 	pm_runtime_mark_last_busy(core->dev);
 
-	rocket_pc_writel(core, OPERATION_ENABLE, 0x0);
-	rocket_pc_writel(core, INTERRUPT_CLEAR, 0x1ffff);
+	scoped_guard(mutex, &core->job_lock) {
+		/*
+		 * Stopping the block belongs under the lock. hw_submit() writes
+		 * OPERATION_ENABLE too, and outside the lock this zero can land
+		 * after that one and stop a task that has only just started.
+		 */
+		rocket_pc_writel(core, OPERATION_ENABLE, 0x0);
+		rocket_pc_writel(core, INTERRUPT_CLEAR, 0x1ffff);
 
-	scoped_guard(mutex, &core->job_lock)
 		if (core->in_flight_job) {
 			if (core->in_flight_job->next_task_idx < core->in_flight_job->task_count) {
 				rocket_job_hw_submit(core, core->in_flight_job);
@@ -360,6 +365,7 @@ static void rocket_job_handle_irq(struct rocket_core *core)
 			pm_runtime_put_autosuspend(core->dev);
 			core->in_flight_job = NULL;
 		}
+	}
 }
 
 static void
-- 
2.43.0