[PATCH v4 1/2] drm/panthor: Replace sleep locks with spinlocks in fdinfo path

["Adrián Larumbe" <adrian.larumbe@collabora.com>]

Commit 0590c94c3596 ("drm/panthor: Fix race condition when gathering fdinfo
group samples") introduced an xarray lock to deal with potential
use-after-free errors when accessing groups fdinfo figures. However, this
toggles the kernel's atomic context status, so the next nested mutex lock
will raise a warning when the kernel is compiled with mutex debug options:

CONFIG_DEBUG_RT_MUTEXES=y
CONFIG_DEBUG_MUTEXES=y

Replace Panthor's group fdinfo data mutex with a guarded spinlock.

Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
Fixes: 0590c94c3596 ("drm/panthor: Fix race condition when gathering fdinfo group samples")
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
---
 drivers/gpu/drm/panthor/panthor_sched.c | 26 ++++++++++++-------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
index 1a276db095ff..4d31d1967716 100644
--- a/drivers/gpu/drm/panthor/panthor_sched.c
+++ b/drivers/gpu/drm/panthor/panthor_sched.c
@@ -9,6 +9,7 @@
 #include <drm/panthor_drm.h>
 
 #include <linux/build_bug.h>
+#include <linux/cleanup.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/dma-mapping.h>
@@ -631,10 +632,10 @@ struct panthor_group {
 		struct panthor_gpu_usage data;
 
 		/**
-		 * @lock: Mutex to govern concurrent access from drm file's fdinfo callback
-		 * and job post-completion processing function
+		 * @fdinfo.lock: Spinlock to govern concurrent access from drm file's fdinfo
+		 * callback and job post-completion processing function
 		 */
-		struct mutex lock;
+		spinlock_t lock;
 
 		/** @fdinfo.kbo_sizes: Aggregate size of private kernel BO's held by the group. */
 		size_t kbo_sizes;
@@ -910,8 +911,6 @@ static void group_release_work(struct work_struct *work)
 						   release_work);
 	u32 i;
 
-	mutex_destroy(&group->fdinfo.lock);
-
 	for (i = 0; i < group->queue_count; i++)
 		group_free_queue(group, group->queues[i]);
 
@@ -2861,12 +2860,12 @@ static void update_fdinfo_stats(struct panthor_job *job)
 	struct panthor_job_profiling_data *slots = queue->profiling.slots->kmap;
 	struct panthor_job_profiling_data *data = &slots[job->profiling.slot];
 
-	mutex_lock(&group->fdinfo.lock);
-	if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_CYCLES)
-		fdinfo->cycles += data->cycles.after - data->cycles.before;
-	if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_TIMESTAMP)
-		fdinfo->time += data->time.after - data->time.before;
-	mutex_unlock(&group->fdinfo.lock);
+	scoped_guard(spinlock, &group->fdinfo.lock) {
+		if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_CYCLES)
+			fdinfo->cycles += data->cycles.after - data->cycles.before;
+		if (job->profiling.mask & PANTHOR_DEVICE_PROFILING_TIMESTAMP)
+			fdinfo->time += data->time.after - data->time.before;
+	}
 }
 
 void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile)
@@ -2880,12 +2879,11 @@ void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile)
 
 	xa_lock(&gpool->xa);
 	xa_for_each(&gpool->xa, i, group) {
-		mutex_lock(&group->fdinfo.lock);
+		guard(spinlock)(&group->fdinfo.lock);
 		pfile->stats.cycles += group->fdinfo.data.cycles;
 		pfile->stats.time += group->fdinfo.data.time;
 		group->fdinfo.data.cycles = 0;
 		group->fdinfo.data.time = 0;
-		mutex_unlock(&group->fdinfo.lock);
 	}
 	xa_unlock(&gpool->xa);
 }
@@ -3537,7 +3535,7 @@ int panthor_group_create(struct panthor_file *pfile,
 	mutex_unlock(&sched->reset.lock);
 
 	add_group_kbo_sizes(group->ptdev, group);
-	mutex_init(&group->fdinfo.lock);
+	spin_lock_init(&group->fdinfo.lock);
 
 	return gid;
 
-- 
2.47.1