drm/v3d: Disable preemption while updating GPU stats

We forgot to disable preemption around the write_seqcount_begin/end() pair
while updating GPU stats:

  [ ] WARNING: CPU: 2 PID: 12 at include/linux/seqlock.h:221 __seqprop_assert.isra.0+0x128/0x150 [v3d]
  [ ] Workqueue: v3d_bin drm_sched_run_job_work [gpu_sched]
 <...snip...>
  [ ] Call trace:
  [ ]  __seqprop_assert.isra.0+0x128/0x150 [v3d]
  [ ]  v3d_job_start_stats.isra.0+0x90/0x218 [v3d]
  [ ]  v3d_bin_job_run+0x23c/0x388 [v3d]
  [ ]  drm_sched_run_job_work+0x520/0x6d0 [gpu_sched]
  [ ]  process_one_work+0x62c/0xb48
  [ ]  worker_thread+0x468/0x5b0
  [ ]  kthread+0x1c4/0x1e0
  [ ]  ret_from_fork+0x10/0x20

Fix it.

Cc: Maíra Canal <[email protected]>
Cc: [email protected] # v6.10+
Fixes: 6abe93b ("drm/v3d: Fix race-condition between sysfs/fdinfo and interrupt handler")
Signed-off-by: Tvrtko Ursulin <[email protected]>
Acked-by: Maíra Canal <[email protected]>
Signed-off-by: Maíra Canal <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Tvrtko Ursulin

drivers/gpu/drm/v3d/v3d_sched.c

@@ -134,13 +134,17 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue)
 	struct v3d_stats *local_stats = &file->stats[queue];
 	u64 now = local_clock();
 
+	preempt_disable();
+
 	write_seqcount_begin(&local_stats->lock);
 	local_stats->start_ns = now;
 	write_seqcount_end(&local_stats->lock);
 
 	write_seqcount_begin(&global_stats->lock);
 	global_stats->start_ns = now;
 	write_seqcount_end(&global_stats->lock);
+
+	preempt_enable();
 }
 
 static void
@@ -162,8 +166,10 @@ v3d_job_update_stats(struct v3d_job *job, enum v3d_queue queue)
 	struct v3d_stats *local_stats = &file->stats[queue];
 	u64 now = local_clock();
 
+	preempt_disable();
 	v3d_stats_update(local_stats, now);
 	v3d_stats_update(global_stats, now);
+	preempt_enable();
 }
 
 static struct dma_fence *v3d_bin_job_run(struct drm_sched_job *sched_job)