From 6abe93b621ab12e93cf0eb7e42a609b36be32da1 Mon Sep 17 00:00:00 2001 From: Maíra Canal Date: Sat, 20 Apr 2024 18:32:13 -0300 Subject: drm/v3d: Fix race-condition between sysfs/fdinfo and interrupt handler MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In V3D, the conclusion of a job is indicated by a IRQ. When a job finishes, then we update the local and the global GPU stats of that queue. But, while the GPU stats are being updated, a user might be reading the stats from sysfs or fdinfo. For example, on `gpu_stats_show()`, we could think about a scenario where `v3d->queue[queue].start_ns != 0`, then an interrupt happens, we update the value of `v3d->queue[queue].start_ns` to 0, we come back to `gpu_stats_show()` to calculate `active_runtime` and now, `active_runtime = timestamp`. In this simple example, the user would see a spike in the queue usage, that didn't match reality. In order to address this issue properly, use a seqcount to protect read and write sections of the code. Fixes: 09a93cc4f7d1 ("drm/v3d: Implement show_fdinfo() callback for GPU usage stats") Reported-by: Tvrtko Ursulin Signed-off-by: Maíra Canal Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20240420213632.339941-7-mcanal@igalia.com --- drivers/gpu/drm/v3d/v3d_sched.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'drivers/gpu/drm/v3d/v3d_sched.c') diff --git a/drivers/gpu/drm/v3d/v3d_sched.c b/drivers/gpu/drm/v3d/v3d_sched.c index b9614944931c..7cd8c335cd9b 100644 --- a/drivers/gpu/drm/v3d/v3d_sched.c +++ b/drivers/gpu/drm/v3d/v3d_sched.c @@ -114,16 +114,23 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue) struct v3d_stats *local_stats = &file->stats[queue]; u64 now = local_clock(); + 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); } static void v3d_stats_update(struct v3d_stats *stats, u64 now) { + write_seqcount_begin(&stats->lock); stats->enabled_ns += now - stats->start_ns; stats->jobs_completed++; stats->start_ns = 0; + write_seqcount_end(&stats->lock); } void -- cgit v1.2.3